sailboat heeling angle

No products in the cart.

Sailing Ellidah is supported by our readers. Buying through our links may earn us an affiliate commission at no extra cost to you.

Everything You Need To Know About Sailboat Heeling

A sailboat will  heel  or  lean over at an angle when you sail in any direction other than almost straight downwind. The wind pressure on the sails will force the vessel to a sideway angle, while the righting moment of the keel’s weight and lateral resistance in the water counteracts this energy. When a sailboat tilts over like this, it is called  heeling .

For a beginner, heeling over can be intimidating and feel unnatural, and I have seen many white faces on their first sailing trip . I certainly remember my heart beating a bit faster during my first sailing experience.

In this article, I’ll explain everything you need to know about sailboat heeling. I’ll xplain why it happens, and how to control and use it to your advantage. We’ll also cover how to adjust your sails and rigging to reduce or increase heeling, and how to deal with different conditions effectively.

Why do sailboats heel over?

To be able to sail at any angle to the wind, a sailboat needs to take advantage of the wind’s force in the sails to make it move forward.

When air hits the sails at the right angle, it generates lift. Some of the energy will force the boat forward, and the rest will try to push the boat sideways through the water. However, the sailboat’s keel prevents lateral movement sideways to a certain degree, and the remaining energy will make the boat move forward at a sideway angle.

The closer to the wind you sail, the more you heel. As you fall off and start pointing away from the wind, the boat’s heeling angle decreases. Eventually, you will reach a point where you are sailing directly downwind, and the keel doesn’t need to work as hard to provide lateral resistance and move the boat forward because the wind is already blowing in the direction you want to go.

What is the optimal heeling angle?

Some boats like catamarans, trimarans, and planing racing monohulls are designed to be sailed primarily upright. Most cruising monohulls, however, are displacement boats and have to heel to go forward when sailing at an angle to the wind.

Most cruising sailboats generally have an optimal heeling angle of 10-20 degrees. When sailing close-hauled , you might have to push it down to 25 degrees to keep your forward motion, but heeling too far will probably make you slower. 10-15 degrees is a good compromise between performance and comfort.

We have a simple method to find the best heeling angle for our particular boat in the conditions we are sailing. When the boat heels over, it will try to turn itself back up by turning into the wind. This is called  weather helm .

To keep the boat straight on course, we compensate for the weather helm by countersteering with the rudder, which also generates more lift up to a certain point. Compensating too much makes the rudder act like a break, which will slow us down.

Keeping the angle of the rudder between 2 and 7 degrees gives you a nice balance between performance and heeling angle. On many cruising boats with a steering wheel, keeping your center mark between ten and two o’clock is an excellent rule of thumb.

How do you control heeling on a sailboat?

There are several ways to control and reduce the heeling angle when sailing, and there are good reasons why we want to.

A typical scenario is when you are sailing with a good balance on the helm at a decent heeling angle. Then, all of a sudden, the wind increases, and the boat starts to heel excessively. As a result, you get more weather helm as the boat tries harder to round up into the wind, and the wheel gets hard to control.

The boat is now overpowered, and you are heeling too much.

Luckily, we have three easy ways to prevent the boat from heeling too much:

• Adjust sail trim
• Adjust course
• Reduce sail area by reefing

Let us take a look at each of our options.

1. Adjust the sails

De-powering the jib or genoa by easing off the sheets or letting out the mainsail traveler is a quick way to regain control over the boat. If you sail on a reach, easing the sheets will turn the sideway force into forwarding force. When eased far enough, you are actively releasing the wind out of the sail, and the sail will start to luff.

When sailing downwind, easing the sheets is the only viable way to de-power the sails quickly, as you might be unable to turn the boat around and back into the wind. If you get too overpowered, you risk broaching, which can be dangerous.

If the wind increase was just temporary gusts, you might want to either actively work on releasing and pulling the sheets, often referred to as “pumping,” or settle for lower performance and slacker sheets. When you sail upwind, this works as a quick way to de-power the sails, but working with the sheets for every gust means you will lose height and not point well.

This article from Savvy Navvy explains broaching very well and has several videos displaying different broaching situations.

2. Adjust the course

Turning the boat into the wind will take power out of the sails and is easy to do when sailing upwind. When we sail close-hauled, we have a trick we can apply to increase our performance.

A powerful ” feathering ” technique is simple to apply and works well when sailing upwind. Instead of easing the sheets in a gust, you keep the sheet tension and steer the boat higher into the wind. As the apparent wind angle moves aft when the strength increases, we use this to our advantage to keep our height by sailing to the angle of our heel instead of the angle of the wind.

I wrote an article about how high a sailboat can point that you might be interested in :  How High Can A Sailboat Point?

Feathering requires an active and focused helmsman, and as soon as the gust stops, you have to fall off again to keep your heeling angle and not lose power in the sails.

Continuing to fall off and bear away while easing off the sheets will also calm the boat down and make it turn more upright. This technique is helpful if you get tired or feel like you are pushing yourself and the boat too hard. Adjusting the course to a downwind point will also reduce the apparent wind speed and can be a good solution if you need a break.

3. Reduce sail area by reefing

When the wind isn’t just gusting but steadily increasing, it is about time to reduce your sail area by reefing. If the boat is heeling more than 20-25 degrees, you have too much canvas exposed, and reefing at this point will make you sail faster, safer, and more comfortably.

It is advisable to reef earlier rather than later as it can be hard to control the boat when it gets overpowered. Pushing limits while sailing is only for experienced people, and any seasoned cruiser agrees that a conservative approach to increasing weather is smart. If you ask yourself, “Should I take a reef?” the answer is always a big yes.

The reef can easily be shaken out if your hunch was wrong or if it was just some gusts or a short squall. Conservative and safe are the magic keywords. Even if you aren’t anywhere near the maximum heeling angle, less sail area can give you a much more comfortable ride with less heel, even if it means sacrificing a little bit of speed.

How far can a sailboat heel before capsizing?

I get this question a lot, especially from those sailing for their first time. When sailing close hauled, we sometimes push the boat to the point where it may seem like we will tip over and capsize. I often see faces going white when the toe rail dips into the water… Luckily, sailboats are designed very cleverly.

The wind can not heel a sailboat over far enough to capsize. Sailing boats are designed to round up into the wind if they are overpowered   and heeling too much.

It is nearly impossible to fight the helm hard enough for the boat to tip over, even if you want to. And if you could, the rudder will eventually lose grip in the water, and the boat will round up until it points upright into the wind with its sails fluttering.

However, you want to be careful when sailing downwind, especially with a spinnaker. As you are sailing off the wind, your apparent wind is lower than your true wind, and sometimes, it can be hard to notice wind increases. Since the boat doesn’t heel over as much as it does upwind, everything might seem fine until you suddenly are overpowered and going too fast.

Getting overpowered can lead you to a broach, which can knock you over in extreme cases, especially if the waves are big. A keelboat will turn itself around again, but you will probably lose your mast and sails, and we want to avoid that!

Monohull sailboats do heel, and they have to in order to generate forward momentum. How far they heel dramatically depends on the boat. They won’t tip all the way over, even if it may seem so, and will usually round themself up into the wind, where you will be left upright with fluttering sails.

Heeling too much is unsuitable for comfort or speed, and finding a good balance of sail area and weather helm will give you the smoothest ride. Be careful, reef early, and don’t push the limits. Sail your boat conservatively until you gain more experience, and remember to enjoy yourself on the water.

If you want to learn more sailing basics, visit my beginner’s guide here.

Sharing is caring!

Skipper, Electrician and ROV Pilot

Robin is the founder and owner of Sailing Ellidah and has been living on his sailboat since 2019. He is currently on a journey to sail around the world and is passionate about writing his story and helpful content to inspire others who share his interest in sailing.

This is great, easy to understand and is helpful for my comfort level!!!

Thank you for your kind words, I’m glad you liked it!

Hey there, Natalie from Social Busy Bee, your partner in the exciting world of Instagram growth. I’ve unearthed something phenomenal for skyrocketing your Instagram profile and I’m thrilled to share it with you!

Social Growth Engine introduces a revolutionary service that propels your Instagram engagement to new heights. It’s a breeze:

– Focus on designing unforgettable content. – Extremely budget-friendly at a mere $36/month. – Safe and secure (no password needed), highly efficient, and Instagram’s best friend.

I’ve witnessed extraordinary results firsthand, and I’m sure you will too! Boost your Instagram presence this instant: http://get.socialbuzzzy.com/instagram_booster

Warm regards, Your ally Natalie”

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Sailboat Heeling Explained In Simple Terms (For Beginners)

If you are new to sailing, then there are many sailing-related terminologies that you will need to learn.

One of those terms is ‘heeling.’ In this article, we will explain what sailboat heeling is and how to control your sailboat when it heels over.

Here is What “Heeling” in Sailing Means:

Heeling is the term used for when a sailboat leans over to either side (port or starboard) in the water by the excess force of the wind. Heeling is normal and counterbalanced by the sailboat’s keel or the crew’s weight distribution on a dinghy.

Table of Contents

What Exactly Makes A Sailboat Heel?

All sailboats are designed to heel, but a sailboat heels over when there is too much wind in the sails, forcing the boat to lean over and lose the harnessed wind power to move it forward.

As a boat heels, the wind pressure on the sails decreases because the sails present a smaller area and less resistance to the wind. The further the boat heels (or leans over), the less pressure.

In addition, boats with a keel have lots of ballast, or weight, to keep them upright in all but the strongest of wind or hurricane conditions. All sailboats will heel or lean over in strong winds, sometimes so far that the rail will dip into the water, and waves will wash onto the deck.

Heeling is simply a part of sailing, and many sailors enjoy it, especially when racing.

How Do I Keep My Sailboat From Heeling?

While all sailboats are designed to heel, sailors can use various techniques to reduce the amount of the angle of the heeling.

These techniques include the following:

Feathering Upwind – 

One of the quickest and easiest techniques a skipper can do in a strong gust of wind is to steer the boat a bit more into the direction of where the wind is coming.

This is called feathering upwind. Doing this releases or spills the wind out of the sails and decreases the wind’s pressure on the sails. This will cause the sails to flap and make a lot of noise (called luffing).

Luffing the sails too much can cause damage to the sails, so this technique is a temporary quick fix and not a long-term solution.

Easing the Mainsheet or the Traveler – 

Another quick technique is to change the angle of the mainsail so that it releases more wind and eases the pressure on the sail.

You can do this by letting out the main sheet (easing the mainsheet) or releasing or easing the traveler control sheet. Both methods will change the angle of the mainsail, releasing the wind pressure and causing your boat to sail more upright.

After a strong gust of wind has passed, you will be able to pull in the mainsail again quickly, to carry on sailing on course.

Reefing the Sails – 

Reefing the sails is a technique used to see or feel that the wind is building or getting stronger. Reefing entails making your sail area smaller, which will work differently on different boats depending on the boat’s set-up.

Reefing the headsail or jib will depend on whether the sailboat has a roller furler or hank on sails. If the boat has hank on sails, you will need to change the headsail to a smaller sail or even a storm jib. Today, most sailboats are equipped with a roller furling headsail, making the headsail sail area smaller.

You can ease the headsail sheet and pull on the roller furler out hauler to roll in the sail a couple of times. This is the equivalent of changing to a smaller sail.

Reefing the mainsail is a little more complicated. Mainsails generally have 2 – 3 reefing points which are stitched in when the sails are made.

The mainsail will need to be partially dropped to access these reefing points, but first, you will need to turn the boat to face the oncoming wind to take the pressure off the sail.

Once you have partially dropped the mainsail, you will need to hook in the reefing point at the mast, haul in the corresponding reefing line, and then retain the main halyard, which is the rope that holds up the mainsail.

How Much Should A Sailboat Heel?

Every sailboat is different, so the exact heel angle for each sailboat will differ.

However, the answer is probably somewhere between 15 and 25 degrees for a comfortable ride in real terms. Thirty degrees is considered the maximum heel for a keel sailboat, depending on the boat’s specific build, design, and characteristics.

Multihulls or catamarans need to be sailed at minimal heel angles; otherwise, they risk capsizing.

But practically, there is a much simpler way to know when your boat is heeling over too far. If you have to fight the steering, otherwise known as the helm, you are heeling too far, and you will need to adjust your sails or course concerning the wind.

How Much Heel Is Too Much?

Similarly, how much heel is too much will also depend on the type of sailing you do. Long-distance cruising, where your boat is your home, will typically involve less heeling than a racing monohull rounding the cans.

However, the amount a sailboat should heel is not opinion. All sailboats are designed to sail at a specified angle of heel. Each sailboat design is for a specific purpose, whether racing, cruising, or somewhere in between, and at their optimum heel angle, there is a minimum wet surface on the boat.

The sails are at a maximum exposure to the wind. When you are sailing and are not at the desired angle, the sailboat is not performing at its full potential.

In addition, if your boat is heeling too much, the boat will become difficult to steer and will slow down. So it’s better to make the necessary adjustments to make yourself and your crew more comfortable and go that little bit faster!

How Far Can A Sailboat Heel Before Capsizing?

For the sake of this article, when we refer to sailboats, we are referring to sailboats with keels and heeling.

Unlike small sailing dinghies, sailboats are designed to heel over without capsizing.

A sailboat is designed to comfortably heel at a certain angle, usually between 15 – 25 degrees. Heeling over more than this is uncomfortable and slows the boat down.

Generally, sailboats with keels can not tip over or capsize under normal sailing conditions. This is because of the weight in the keel. The weight of the keel has been designed to counterbalance the force of the wind in the sails. Plus, the more a boat heels over, the less pressure there is in the sails, and the keel will bring the boat to face into the wind where there is less pressure on the boat overall.

However, this does not mean a sailboat cannot capsize. There are stories of sailboats being knocked down in big waves and strong winds, but this is often temporary as the sailboat will often self-right or come upright by itself.

Extreme conditions such as gale-force winds combined with big seas, too much sail out, and waves crashing over the boat and flooding the cockpit may all combine to capsize a sailboat.

Learning to Sail: Heeling Over

How To Reef A Sail – A Beginners Guide

Click to share...

Understanding Heeling in Sailing Explained

Have you ever wondered what is heeling in sailing ? In this article, we will delve into the fascinating concept of heeling and how it impacts sailing. Whether you are a seasoned sailor or new to the sport, understanding heeling is crucial for a safe and enjoyable sailing experience.

Key Takeaways:

• Heeling refers to the leaning or tilting of a sailboat due to the wind pressure on the sails.
• Sailboats are designed to heel to a certain degree, and heeling can be controlled through various techniques such as feathering upwind and adjusting sail trim.
• The optimal heeling angle for a sailboat is typically between 15 and 25 degrees.
• Excessive heeling can impact the boat’s performance and stability, so it is important to find a balance.
• Understanding the effects of heeling and employing proper techniques can enhance your sailing experience.

What Exactly Makes A Sailboat Heel?

Sailboats heel when there is too much wind in the sails, causing the boat to lean over and lose some of its forward momentum.

The wind pressure on the sails decreases as the boat heels, resulting in less pressure and force. The extent of heeling depends on factors such as the wind strength and the boat’s design and characteristics.

The keel of a boat provides stability and counteracts the heeling force by its weight and lateral resistance in the water. The optimal heeling angle for a sailboat is usually between 15 and 25 degrees , but it may vary based on the boat’s specific build and design.

“Sailboats heel when there is too much wind in the sails, causing the boat to lean over and lose some of its forward momentum.”

How Do I Keep My Sailboat From Heeling?

While heeling is a natural part of sailing, there are several techniques that sailors can use to control and reduce the angle of heeling. These techniques are essential for maintaining stability and ensuring a smooth sailing experience. Here are some tips to keep your sailboat from heeling excessively:

• Feathering upwind: One effective technique to reduce heeling is to steer the boat slightly into the direction of the wind. This technique releases or spills the wind out of the sails, reducing the pressure and decreasing the angle of heeling.
• Easing the mainsheet or traveler: By adjusting the angle of the mainsail, sailors can release wind pressure and allow the boat to sail more upright. This technique helps to counterbalance the force of the wind and reduce heeling.
• Reefing the sails: In strong winds, it is advisable to reduce sail area by reefing the sails. This involves making the sails smaller and reducing the surface area exposed to the wind. Reefing helps to control heeling and maintain stability in challenging conditions.
• Proper sail trim and course adjustment: Paying attention to sail trim and course adjustment is crucial for controlling heeling. Optimal sail trim ensures that the sails are properly adjusted and balanced, reducing the tendency to heel. Adjusting the course can also help in finding the most favorable wind angles and minimizing heeling.

Implementing these techniques and being mindful of sail trim, course adjustments, and prevailing conditions will greatly help in keeping your sailboat from heeling excessively. By maintaining control over heeling, you can enhance both the comfort and safety of your sailing experience.

How Much Should A Sailboat Heel?

The optimal heel angle for a sailboat depends on its specific design and purpose. In general, a comfortable and efficient heel angle for most sailboats is between 15 and 25 degrees. Sailboats with keels are specifically designed to operate within a particular heel angle to maximize their performance and stability.

Going beyond the maximum heel angle recommended for a sailboat can have negative consequences. It can make the boat difficult to steer and slow down its speed. Maintaining control and stability is crucial while sailing, and reducing excessive heeling becomes essential.

To reduce heeling, sailors can employ various techniques that have been mentioned earlier in this article. Feathering upwind, easing the mainsheet or traveler, and reefing the sails are effective methods for decreasing the angle of heeling. Additionally, adjusting the sails and course according to the wind conditions is vital to maintaining control and stability.

By implementing these techniques, sailors can effectively reduce heeling and ensure safer and more enjoyable sailing experiences.

Expert Tip:

“Proper sail trim and course adjustment are critical for controlling heeling on a sailboat. Understanding the balance between sail area, weight distribution, and wind pressure is key to maintaining stability and reducing excessive heel. Always adjust your sails and course according to the prevailing wind and sea conditions to ensure a smooth and controlled ride.”

Heel Angle Guidelines:

These guidelines provide a general framework for understanding the optimal heel angles for different types of sailboats. However, it’s important to refer to the specific manufacturer’s recommendations for your sailboat to ensure accurate and safe sailing practices.

How Much Heel Is Too Much?

The acceptable heel angle for a sailboat depends on various factors, including the type of sailing and the specific boat design. Long-distance cruising boats may experience less heeling compared to racing monohulls. However, all sailboats are designed to sail at a specific angle of heel. Going beyond this angle can impact the boat’s performance and comfort. Excessive heel can make the boat difficult to control, slow it down, and create excessive strain on the rigging. It is important to find a balance between performance and comfort by making necessary adjustments to the sails and course to reduce excessive heeling.

How Far Can A Sailboat Heel Before Capsizing?

Sailboats with keels are designed to heel over without capsizing under normal sailing conditions. The weight of the keel provides stability and counterbalances the force of the wind in the sails. The boat’s rigging and design also play a role in preventing capsize. However, extreme conditions such as gale-force winds, large waves, and excessive sail area can potentially capsize a sailboat. In such situations, a sailboat may temporarily be knocked down or capsized, but it often self-rights or comes upright by itself. It is important to sail within safe limits and take appropriate measures, such as reefing the sails and reducing sail area, to avoid capsizing.

“Sailboats are designed to heel to a certain degree, and their stability depends on various factors such as keel design, weight distribution, and sail area.” – John Smith, experienced sailor

• Regularly check weather conditions and forecasts before setting sail to avoid unpredictable or extreme conditions.
• Practice proper sail trim and adjust the sails according to wind strength and direction to maintain control and stability.
• Ensure the boat’s rigging is in good condition and properly maintained for optimal performance and safety.
• Consider taking sailing courses or seeking guidance from experienced sailors to improve your understanding of heeling and sailing techniques.

How to Control Heeling on a Sailboat

To control and reduce heeling on a sailboat, sailors can utilize various techniques and adjustments to maintain control and stability. Here are some helpful tips for controlling heeling in sailing and reducing excessive tilt:

• Feathering Upwind: When sailing upwind, slightly steer the boat into the direction of the wind. This technique releases or spills wind out of the sails, decreasing the pressure and reducing heeling.
• Easing the Mainsheet or Traveler: Adjusting the mainsheet or traveler changes the angle of the mainsail, releasing wind pressure and allowing the boat to sail more upright. Experiment with different positions to find the optimal balance.
• Reefing the Sails: In strong winds, reefing the sails helps reduce their area, making them smaller and less prone to catching excessive wind. This can significantly decrease heeling and maintain control.
• Proper Sail Trim and Course Adjustment: Pay attention to sail trim by adjusting the sheets and halyards to achieve an optimal shape. Proper course adjustment ensures the boat is sailing at the correct angle to minimize heeling.

Understanding the balance between sail area, weight distribution, and wind pressure is key to controlling heeling on a sailboat. Sailors should also consider the specific design and characteristics of their boat, as well as the prevailing wind and sea conditions when making adjustments to sail trim and course.

Monitoring Wind Strength with a Masthead Wind Indicator

A masthead wind indicator can be a useful tool for sailors to monitor wind strength and make necessary adjustments. This device is typically mounted at the top of the mast and provides visual indication of wind direction and intensity. By keeping an eye on the wind indicator, sailors can quickly respond to changes in wind conditions, allowing for proactive adjustments to control heeling.

Remember, every sailboat is unique, so it may take some experimentation and practice to find the optimal combination of techniques and adjustments that work best for your specific vessel. By mastering the art of controlling heeling, you can enhance your sailing experience and ensure a safe and enjoyable journey.

Tips for Controlling Heeling in Sailing – A Quick Reference Guide

Heeling is a fundamental aspect of sailing, resulting from the force of the wind on the sails causing a sailboat to lean or tilt. Sailboats are designed to manage heeling within a certain range, and it is crucial for sailors to comprehend how to control and adjust it to ensure optimal performance and stability. By implementing techniques such as feathering upwind, adjusting sail trim, and reefing, excessive heeling can be reduced. Understanding the unique characteristics and design of your boat, as well as considering prevailing wind and sea conditions, allows for necessary adjustments and ensures a safe and enjoyable sailing experience.

Learning to respond effectively to heeling not only allows sailors to maintain control but also enhances their understanding of sailboat dynamics. Being aware of how heeling influences a sailboat’s behavior is vital for maintaining balance and maneuverability. Sailors must strike the right balance between heeling and stability to achieve the best sailing experience. By mastering the techniques to control heeling and making informed decisions based on prevailing conditions, sailors can navigate the waters with confidence and efficiency.

Understanding heeling in sailing is of utmost importance for sailors of all levels. It not only affects the performance and maneuverability of the boat but also ensures the safety and comfort of everyone on board. By embracing the art of sailing, sailors can harness the power of the wind while maintaining control over their vessel. So, whether you’re a seasoned sailor or new to the sport, take the time to learn and understand heeling, and embark on unforgettable sailing adventures with confidence and skill.

What is heeling in sailing?

Heeling in sailing refers to the leaning or tilting of a sailboat to either side (port or starboard) due to the force of the wind. It is a natural occurrence caused by the wind pressure on the sails.

What exactly makes a sailboat heel?

Sailboats heel when there is too much wind in the sails, causing the boat to lean over and lose some of its forward momentum. The wind pressure on the sails decreases as the boat heels, resulting in less pressure and force. The extent of heeling depends on factors such as the wind strength and the boat’s design and characteristics.

How do I keep my sailboat from heeling?

Sailors can control and reduce heeling by using various techniques such as feathering upwind, easing the mainsheet or traveler, and reefing the sails. Proper sail trim and course adjustment are also crucial for controlling heeling.

How much should a sailboat heel?

The optimal heeling angle for a sailboat is typically between 15 and 25 degrees, but this may vary depending on the specific boat design and conditions. Sailboats with keels are designed to heel over without capsizing, as the weight of the keel provides stability and helps the boat face into the wind.

How much heel is too much?

Going beyond the maximum heel angle can make the boat difficult to steer and slow it down. To reduce heeling, sailors can employ techniques such as feathering upwind, easing the mainsheet or traveler, and reefing the sails. Adjusting the sails and course according to the wind conditions is essential for maintaining control and stability while sailing.

How far can a sailboat heel before capsizing?

Sailboats with keels are designed to heel over without capsizing under normal sailing conditions. However, extreme conditions such as gale-force winds, large waves, and excessive sail area can potentially capsize a sailboat. It is important to sail within safe limits and take appropriate measures to avoid capsizing.

How to control heeling on a sailboat?

Sailors can control and reduce heeling by adjusting the sails through techniques such as feathering upwind, easing the mainsheet or traveler, and reefing the sails. Proper sail trim and course adjustment are crucial for maintaining control and stability. It is important to consider the specific boat design and characteristics, as well as the prevailing wind and sea conditions, when adjusting sail trim and course.

Source Links

• https://www.godownsize.com/sailboat-heeling-simple-terms/
• https://sailingellidah.com/sailboat-heeling/
• https://forums.sailboatowners.com/threads/heeling-explained.144031/

Nicholas Finn

I've been the captain of a fishing boat for over 20 years, and I created Pirateering to share my knowledge of and interest in seafaring.

Recent Posts

Safe Time for Shrimp Out of Fridge - Know Limits

Proper storage of shrimp is essential for ensuring food safety and maintaining its freshness. As seafood lovers, we want to enjoy the delicious taste of shrimp without compromising our health. That's...

Safe to Leave Shrimp Out Overnight? Find Out!

When it comes to food safety, understanding proper storage guidelines is crucial. If you've ever wondered whether it's safe to leave shrimp out overnight, we're here to provide you with the...

What is Angle of Heel on a Sailboat

And, what Angle of Heel on a Sailboat is acceptable?

What is heeling over on a sailboat?

Heeling over or “heeling” on a sailboat is when it leans over.

Why does a sailboat heel over and why doesn’t it tip over?

Remember your tommee tippee cup? It had a rounded bottom and a weight loaded into the rounded bottom. No matter how much water you put in the cup, the weight at the bottom made sure the cup stood upright – and the rounded bottom meant that if you pushed it over, it would stand right back up.

Your finger pushing sideways on the top of the cup is just like the wind acting on the sails. The wind acting on the sails puts pressure on the sails. Pressure over the entire area of the sails creates a force. The greater the area, the greater the force, and the stronger the wind, the stronger the force. The distance the force is collectively acting on the sails is about 1/3 of the way up the sails. This point is called the center-of-pressure. This is like your finger pushing all the wind’s force at that center-of-pressure point. The sailboat, like the tommee tippee cup has no choice but to lean (heel) over.

The propensity for the sailboat to heel over depends on the height (distance) of the center of pressure above the water line. The physics formula for this is force x distance which equals a physics term called “moment” (not like a moment in time). The “moment” can be considered as the same as “torque” or even easier – as the “tipping force” or (heeling force). The greater the distance and force – the bigger the tipping force.

In high wind conditions, you can lower the center of pressure by spilling some of the wind out of the top of the sails by twisting out the sail at the top (done by easing the mainsheet which allows the boom aft to rise – thus creating less tension on the leech of the sail and allowing the top to twist out).

Twisting out the top of the sail has a double effect. There is less sail area presented to the wind at the top. This means a lower center-of-pressure (less height) and less area – giving rise to less tipping moment.

Another way to lower the center of pressure is to reef the sail (partially lower it). This also acts to reduce the area of the sail. Less area and less height of the center-of-pressure reduces the tipping force. Here is an image showing reefing and twisting effect on the tipping moment. The image also discusses how twisting and reefing moves the center-of-pressure forward. This has the added benefit of reducing what is known as weather helm – the boat wants to automatically turn up into the wind.

What stops the sailboat from completely tipping over?

A balance between gravity acting on the weighted keel and the wind force on the sail stops the boat from completely tipping or heeling over. As the boat heels over, the sail area is not upright and so less sail area is presented to the wind. Also as the boat heels over, gravity acting on the weighted keel that is rolling upwards with the heel of the boat creates a force to stand the boat back upright. At some point, both forces meet in agreement and compromise with a defined heeling angle.

Imagine the weighted keel is just like how your Tommee Tippee cup uses gravity to force the boat to stand back upright. Thus it becomes a balance between the boat being pushed over by the force on the sails and the weight of the keel trying to stand it back up.

See this animation below of the balance of forces. CLICK on the green Increase Wind button. You will see how the “righting force” increases as the weighted keel lifts outwards off the centerline. You’ll also see how the tipping force decreases because less sail area is presented face-on to the wind. It means that the righting force from the keel will always overpower the wind force at some angle of heel. This is not to say that sailboats never tip over, they do but only usually in cases of a massive unprepared-for gust (60+ knots), giant wave, or if they lose their keel. Dinghies of course do tip over from the improper balance of the crew.

What is an acceptable heel angle?

The acceptable angle of heel on a sailboat depends on various factors, including the design of the boat, its ballast, the boat’s purpose, and the prevailing conditions. Generally, here are some guidelines:

• Dinghies and Small Boats : Dinghies are designed to be agile and may heel significantly, especially when sailed aggressively. Capsizes can happen but are often a part of dinghy sailing.
• Cruising Sailboats : Most cruising sailboats are designed to be stable and comfortable. They typically perform best at an angle of heel between 10° and 20°. Once a cruising boat heels beyond 20°, its weather helm tends to increase, making it more challenging to steer, and the boat might not sail as efficiently.
• Racing Sailboats : Racers might push their boats harder, and some racing designs can handle more heel. Nevertheless, excessive heel can still decrease speed as more wetted surface (hull in the water) causes increased drag.
• Multihulls (Catamarans and Trimarans) : These vessels are designed to sail relatively flat. Heeling angles over 10° can be a cause for concern on a multihull. When a multihull starts to heel significantly, there’s a risk of capsize, especially if a hull lifts entirely out of the water.
• Keel Design : Boats with full keels tend to be more stable and resist heeling more than those with fin keels or lifting keels. However, once they reach a certain heeling point, full keel boats can be more challenging to bring back upright.
• Seaworthiness : Some boats, especially bluewater cruisers, are designed to be very seaworthy and can handle significant heel angles, even beyond 45°, without capsizing. Still, this doesn’t mean it’s comfortable or efficient to sail them at such angles.

Factors like gusty winds, big waves, and the condition of your sails (e.g., having a full mainsail up in strong winds) can also influence heel.

What to do if you are getting excessive heeling angle:

• Reef Early : Reducing sail area can help to decrease heeling and make the boat easier to control.
• Adjust Sail Trim : Flatten your sails by tightening the outhaul, cunningham, and backstay (if adjustable).
• Change Your Point of Sail : Sailing more downwind can reduce heeling, but be cautious about accidental jibes.
• Ease the Sheets : Letting out the mainsheet or headsail sheet can reduce power in the sails.

Lastly, the best way to understand how much heel is acceptable for your specific boat is to gain experience in various conditions and, if possible, consult with more seasoned sailors or trainers familiar with your type of boat.

This information was drawn from the NauticEd Skipper Course (for large keelboats) and the NauticEd Skipper Small Keelboat Course . Sign up now to learn the knowledge you need to know to effectively skipper a sailboat.

• Recent Posts

• Sail on the Clipper Stad Amsterdam - January 26, 2024
• Catamaran Vacation Training in Puerto Rico - January 6, 2024
• Catamaran Sailing Training in Houston Texas - January 2, 2024

TWEET ABOUT

FIGHT CHILDHOOD CANCER

NauticEd is a fully recognized education and certification platform for sailing students combining online and on-the-water real instruction ( and now VR ). NauticEd offers +24 online courses , a free sailor's toolkit that includes 2 free courses, and six ranks of certification – all integrated into NauticEd’s proprietary platform. The USCG and NASBLA recognize NauticEd as having met the established American National Standards. Learn more at www.nauticed.org .

The NauticEd Vacations team are Expert Global Yacht Charter Agents – when you book a sailing vacation or bareboat charter through NauticEd, we don’t charge you a fee – we often save you money since we can compare prices from all yacht charter companies. PLUS, we can give you advice on which destination or charter company will suit your needs best. Inquire about a Sailing Vacation or Charter .

Online Sailing Courses Sailing Vacations | Charters Practical Sailing Courses Sailing Certification | License

Sign up for 2 FREE Sailing Courses Try sailing in Virtual Reality! Gift a Friend a Sailing Course Sailing Events | Opportunities

About NauticEd Contact Us NauticEd Support Privacy Policy

• Learn to Sail Memberships
• Private Lessons
• Online Learning
• Group Sails, Racing & Events
• Memberships
• Reciprocal Privileges
• Members Only
• Tahiti May 2024
• Croatia September 2024
• British Virgin Islands December 2024
• Skippered Sails
• Corporate Events

Optimal Angle of Heeling

By andrew lesslie.

Have you noticed how some sailors stretch out ahead upwind, while others fall back?

Part of making good progress upwind is keeping the boat to an optimal angle of heel. Too little and you give up power, too much and you might feel fast, but are losing height.

The Merit 25 is wide at the waterline, but has little flare from the waterline to the sheerline. If the boat is heeled too far, the buoyancy concentrated close to the waterline lifts the keel and rudder to the surface very easily.

Take a look at the shot below and note the white water exiting from just astern of the keel. This is indicative of an abrupt and uncontrolled release of pressure from behind the keel, showing that at this, excessive heel angle the boat is unable to convert the drive from the sails to forward motion.

So what does that look like from astern? Here we can clearly see that the underside of the boat on the windward side is entirely out of the water.     Note also the pressure wave that flowing from the rudder, indicating that the boat is sliding sideways and making leeway rather than driving to windward.

In their defense, this boat is lightly crewed and is cruising, they’re dealing with gusts by feathering up into the wind rather than actively trimming.   Note also the loose mainsail luff and very full sails.  Neither is conducive to upwind performance.

So what should you be aiming for? A good heel angle for the Merit 25 is 15° – 20°, less than you would heel a J/24. 

When you find your heel angle exceeding this, move crew weight to windward, flatten the sails and keep the main sheet out of the cleat so your trimmer can ease in  the puffs and sheet back in during the lulls.

In gusty conditions, the benefits from active mainsheet trimming typically exceed the benefits of the extra crew member on the rail.    

The bonus of having another crew member in the cockpit is that they can watch the compass while teh skipper concentrates on driving and can glance regularly under the jib for boats and obstacles.

Learn About Upcoming Events

• 451 Seaport Court
• Redwood City, CA 94063
• 650-363-1390
• Rich Ferrari, The Chief
• Bob Diamond, School and Vacations Director
• Dana Ochstein
• Instructors
• Redwood Landing Marina

Copyright © 2021  Spinnaker Sailing Inc. All Rights Reserved.

Torque about Hull Stability

Torque applied about the longitudinal axis leads to heeling, and if the heeling angle is large enough, a boat may capsize. This is considered to be undesirable among all the boat owners I know, and so hull stability is taken to be a matter of some importance. Here, stability refers to the ability of a boat to right itself after having been heeled over by, say, a sudden gust of wind or a sudden change of course. We would like to know how much our boat can heel over before capsizing, and we would like to know how fast she can right herself. I will deal with these questions here. The physics of hull stability is simple in concept but devilish fiddly when it comes to detailed calculations. So, in the spirit advocated in the introduction, I will once again simplify when necessary to make the issues clearer and will relegate math details to the endnotes. The fiddly details have generated much literature, and a number of technical terms have entered the sailor's vocabulary as a consequence. So that you know what is being talked about when these words are uttered, I will begin by introducing them.

Center of Buoyancy and Metacenter

The force of gravity that acts on an extended object, such as your Pud-dleduck or indeed yourself, can be thought of as acting at a particular point, called your center of gravity (CG). This is a familiar idea, and it extends to other forces. Thus, the force that buoys up your boat acts on all parts of the wetted surface but can be thought of as acting at a single point called the center of buoyancy (CB). So far, so good, but as soon as we think about CB a little more deeply, we see that it quickly becomes complicated. Consider figure 5.5. Here, for simplicity I have replaced your beloved Puddleduck with a block of wood—no insult intended— but you will appreciate the reason for this substitution shortly. The block of wood is of such a density that the water line is halfway up when the block is floating in a stable position. The CG is easy to locate: it is simply the geometrical center of the block, assuming uniform density. What about the CB?

The center of buoyancy for a simple shape such as this block is the geometrical center of that portion of the block which is underwater. So, for the initial stable position we can readily mark the CB with an x, as in figure 5.5. Now let us suppose that the block is disturbed and rotates a

Figure 5.5. (a) A floating block in a position of stable equilibrium. The center of gravity, CG, lies in the same vertical plane as center of buoyancy, CB (x). (b) When the box is rotated, its CB moves and is no longer in the same plane as the center of gravity, resulting in a restoring torque. (c) and (d) For increased rotation angles, the CB changes, thus altering the torque that is applied to the box. (e) When the rotation angle is 90° the CG and CB are again aligned and no torque applies. But this position is one of unstable equilibrium.

little, like a heeling hull. This new orientation does not alter the CG at all, but the CB has moved. We can calculate the new CB easily enough for a simple block of wood, but for a complex hull shape it can be impossible to work out with a pen and paper: we would need to resort to number-crunching, which would muddy the pedagogical waters. I show the CB for our block of wood for several different orientations in figure 5.5. That the CB depends on heel angle, whereas the CG does not, has the following consequence. When the two centers are not aligned vertically, the force of gravity and the force of buoyancy (which have the same magni-

Figure 5.6. (a) Center of gravity, CG (open circle), and center of buoyancy, CB (x), for a floating box. If the box is a solid block of wood, the CG is at the geometrical center, in this case chosen to be at the water line. Arrows indicate upward buoyancy force and downward gravity force. These forces are not aligned and therefore apply a torque to the box. The horizontal separation of CG and CB is the righting arm, denoted GZ. (b) If the box was originally in a stable position (outlined in gray), a line from the CG to the top would appear on the rotated box as shown by the slanted dotted line. This line intersects the "new" vertical from the CB at the metacenter (triangle). The distance between CG and the metacenter is metacentric height, denoted GM. If the metacenter is higher than the CG, as here, the box orientation is stable—it will return to its original position. (The righting arm, GZ, is defined as positive or negative depending on whether the metacenter is above or below the CG.)

tude but opposite direction) do not quite cancel out but instead exert a torque on the hull. This torque also depends on the heel angle, which complicates the physical analysis significantly.

We can quantify this dependence of the buoyancy force on the heeling angle in a manner that readily conveys information to the eye, and so is very popular among boat designers. Much of a boat's heeling characteristics can be captured in a graph called a righting arm curve. The righting arm is the horizontal distance between CG and CB, as shown in figure 5.6. It is conventional to denote righting arm by the abbreviation GZ. This distance is important because it is proportional to torque:

increased GZ means increased torque. If GZ is positive then the torque is a righting moment that acts to reduce a boat's heeling angle; if negative then the torque will act to capsize the boat.

How do we decide whether GZ is positive or negative? In other words, how do we know if the torque that is applied by the combined forces of buoyancy and gravity will act to right a boat or capsize it? The answer lies in yet another technical term: metacenter. The metacenter is explained in figure 5.6. The concept is slightly abstract, so I will provide a separate definition of it here. Consider Puddleduck sitting calmly on a flat sea, with her mast vertical. A large wave comes along that causes her to heel over a large amount, as happened to the block shown in figure 5.6. Puddleduck's center of buoyancy moves because when she is heeling, her hull displaces water in a different way than when she is upright, as we have seen. We find her metacenter at the new heeling angle by a simple geometrical construction. The CB acts vertically: we extend a vertical line from the CB to a line through her mast. (Of course, now that she is heeling, her mast is no longer vertical.) The point of intersection of these two lines is the metacenter, denoted by a triangle in figure 5.6.

Righting Arm Curves and Stability

Here is the significance of the metacenter: if it lies above the center of gravity, the torque will right Puddleduck: she will return to her stable upright position. If the metacenter lies below the CG, the torque will cause her to capsize. Of course, the location of the metacenter changes with the heeling angle because the CB changes; that makes it difficult to say what is going to happen by quickly glancing at the equations. However, the stability information is readily conveyed in Puddleduck's righting arm curve, which is a plot of GZ vs. heeling angle. Determining the righting arm curve for a complicated structure like a boat is difficult and depends on every last detail of hull shape and mass distribution. So instead, in figure 5.7, I show the righting arm curve for our block of wood. You can see that the shape of the curve changes as the shape of the block changes. This change is observed also in boats: wider boats show more initial stability, meaning that they are more difficult to tip over. The righting arm curve displays this initial stability in the steepness of the slope near zero heeling angle, amz = 0°. A more stable block or boat has a steeper slope because it has a greater righting moment and so is harder to tip over. Catamarans are very wide and have great initial

Heeling angle (degrees)

Figure 5.7. (a) Righting arm length, GZ, vs. heeling angle, amz, for different floating boxes. If the center of gravity of the box is lowered from the geometrical center (appropriate for a solid block) halfway to the bottom (more appropriate for a boat), the dashed curves result. Black lines correspond to box width and height of (w,d) = (3,2), and gray lines to (w,d) = (3,1). (b) Movement of CB from (x,z) = (0,0) as the heeling angle increases from 0° to 120°.

stability. More slender boats with deeper hulls, like our block of wood in figure 5.6 (with its righting arm curve also plotted in figure 5.7), have less initial stability. They tip over more easily and, as we will soon see, roll more; their roll amplitude and roll period (the time taken to roll back and forth once) are both greater than for a flatter boat, or block.

Note from figure 5.7 that the righting arm curve peaks at a certain heeling angle, corresponding to maximum righting moment, and then decreases as the heeling angle increases further. At these larger angles the boat or block will still try to right itself, so long as the righting arm curve is positive, but the torque is reduced. At some larger heeling angle the curve reduces to zero. At this point there is no righting moment, and the boat or block will stay at this angle if placed there: there is no torque to cause it to turn either way. At still larger heeling angles the curve is negative, corresponding to an overturning or capsizing torque; when a boat or block gets into this region, it cannot right itself. The heel angle at which the righting arm curve dips to zero marks the range of stability for our boat or block. The two characteristics that emerge from righting arm curves—initial stability and range of stability—are key design parameters for boat-builders. Obviously, we would like both to be as large as possible, but it doesn't work like that. I have tried to indicate in figure 5.7 how boat curves differ from those of wooden blocks by lowering the CG of the blocks. This is what would occur if the blocks were hollowed out to form a crude boat hull. The results show as better righting arm curves: greater initial stability, increased righting arms and hence increased righting torque, and greater range of stability. From figure 5.7 we see that flatter, hollow blocks have greater initial stability but a lesser range of stability, and the same is generally true of boats. The message is: go to sea in a boat, not a block—but I guess you already knew that.

Boats differ from blocks in other ways too. The downflood angle is the maximum heeling angle that a boat can have before she swamps. For an open boat, this angle can be quite small: the righting arm curve abruptly ceases instead of smoothly varying out to large heeling angles, as in figure 5.7. The watertight deck on many modern yachts permits much larger heeling angles. Even here, of course, it is necessary to close the hatches. Hatches tend to be placed along the centerline of a yacht, and as high up as practicable, to permit large heeling angles without danger of swamping. Another difference between boats and blocks is much more difficult to quantify. Boats carry movable masses which can shift as the boat heels. Whether it be gas or water in tanks, or cars and trucks on ferries, shifting mass can be very dangerous in a rolling boat. What seems stable can become unstable very quickly, and in the past a number of tragedies have resulted for this reason. To avoid the stability problems that can result from liquid sloshing back and forth, fuel tanks on yachts have baffles placed in them.

Continue reading here: Time to Rock and Roll

Was this article helpful?

Recommended Programs

Myboatplans 518 Boat Plans

Boat Alert Hull ID History Search

3D Boat Design Software Package

Related Posts

• A - Science of Sailing
• More Righting Moment Means Less Heel
• The Age of Exploration Carrack and Caravel
• The Slot Effect - Science of Sailing
• Aerodynamic Lift and Drag
• Carvel versus Clinker - Science of Sailing

• Members Forum
• Log In / Create Account

Sailing the Heel

by Harbor Sailboats | May 30, 2018 | Blog | 0 comments

Submit a Comment Cancel reply

You must be logged in to post a comment.

Latest Blog Posts

• Sailing Lessons in San Diego
• Water in the Bilge
• Bow Standing
• Gear then Steer
• 2024 Club Flotilla- BVI’s

Staying in Control in Breeze

There’s nothing like the leeward rail of a sailboat buried in the water, the tiller or wheel gripped firmly fighting the pressure, or is there? Actually, any top sailor who specializes in making a boat get from point A to point B as quickly and efficiently as possible will tell you that the real secret to speed is balance and control. Even sailors who may not care about making their boat go a 10th of a knot faster upwind can relate to the need for understanding sail trim and sailing technique as an aid to control. Trim and technique allow you to be the master of your boat when it gets windy, instead of the other way around.

Let’s start with the question of how much heel is appropriate. In quantitative terms, the answer is probably somewhere between 20 and 25 degrees maximum for a displacement monohull, depending on boat-specific characteristics. Multihulls and high-performance monohulls need to be sailed at minimal heel angles.

Practically, there is a simpler way to know when the boat is tipping over too far. If you have to fight the helm (a rudder angle of more than five to seven degrees), you are heeling too far and need to adjust trim or technique. Heel equals helm. When the boat leans over, it attempts to turn itself back up into the wind; which is referred to as “weather helm.” To keep the boat going straight, we compensate with the rudder, which is fine up to a point. But the rudder is really a brake. Use too much, and it’s just like dragging a barn door through the water, which is not a particularly fast or efficient way to sail.

All sailboats need an optimum of “X” amount of power. A certain amount of heel allows the boat to sail on her lines and gives the rudder bite and helps create lift. (That’s why you will see racing crews huddled on the leeward rail in light air to induce heel). More than “X” and the extra heel creates drag. Weather helm is the indicator. Sailing with more helm and heel than the optimum can be likened to driving your car down the street on the doors, instead of on the wheels. So, as in all things, we need to strike a balance and find the middle way. So, how does one remain in control?

Ease the sails 

The quickest way to get a sailboat back up on her feet is to ease the sheets. This is especially true when sailing on a reach, when you are attempting to sail more or less in a straight line. Easing mainsail and headsail sheets turns sideways force into forward force. Ease far enough and the sail will luff, spilling excess power. When sailing on a reach, in every puff, the sails can be eased, in part because of the extra horsepower, but also because the apparent wind moves aft. To keep constant rudder pressure and consistent heel, ease in the puffs, and trim in the lulls when reaching. Remember, it is the sails that steer the boat; the rudder is just a fine-tune device.

Feather, don’t fight

Upwind, the problem is a little more complicated. If we ease the sheets every time we get a puff, we will not be able to sail as close to the wind as we would with the sails trimmed in. We’ll go fast, but will not point well. Upwind, there is a powerful steering technique called “feathering” that makes all the difference. Feathering means sailing by angle of heel, instead of maintaining a constant angle to the wind as indicated by the headsail telltales. 

If steering upwind when a puff hits, let the boat head up slowly to balance the helm and maintain a constant angle of heel. Headsail telltales will lift, or “feather,” indicating a slight luff. That’s okay; we don’t need the extra power. As the puff lets off, and the boat begins to get too upright, bear off slightly to maintain heel angle. The telltales will begin to stream aft in their normal upwind position. Use the telltales in the lulls, but maintain angle of heel in the puffs by letting the boat head up.

Flatter sails are less powerful

If you have to ease the sheets when reaching, or do a lot of feathering to keep the boat on her feet, it is time for flatter sails. For the headsail, add halyard tension so as to remove horizontal wrinkles (perpendicular to the headstay). If you have a backstay adjuster, add tension to minimize headstay sag. Move the sheet lead aft to flatten the bottom sections of the sail and allow the top to twist off. For the mainsail, add halyard tension to remove horizontal wrinkles (sound familiar?). Tighten outhaul to flatten the lower third of the mainsail. Add backstay to bend the mast if that is an option.

A little luffing is okay

Remember, you only need “X” amount of power, so it’s okay to let the sail luff a little. Upwind, drop the traveler and allow the mainsail to backwind along the forward 20 to 30 percent. Move the jib lead aft, and let the top of the jib luff slightly. If you need to drop the traveler to balance the boat, the jib lead should move aft to match the shape to the mainsail. Reaching, ease the sheets and allow the sails to luff slightly rather than allowing too much heel. If you have to luff both sails constantly (more than 50 percent of mainsail), it’s time to reduce sail area.

Some heel is good, too much is bad

So, the ultimate answer is some heel is good; too much heel is bad. To paraphrase rather badly from an ancient Zen saying, “As in all things, the correct answer certainly lies in the middle way.”

Questions? Email David Flynn .

This content was originally published on SpinSheet .

The Discussion

Cristal clear for me. Just a quick question: when flattening the main, cunnignam (which you don't touch here) works the same way as to give tension to the halyard? please elaborate. Thanks, Luis

Us, too. We pour that passion into each of our newsletters to help you enjoy sailing even more.

• Anchoring & Mooring
• Boat Anatomy
• Boat Culture
• Boat Equipment
• Boat Safety
• Sailing Techniques

Mastering Sailboat Heeling

Sailboat heeling occurs when a yacht leans to one side under the pressure of the wind against its sails. This significantly affects a vessel’s performance, stability, and safety.

Managing heel angle is essential for sailors to optimize their boat’s performance, maintain control, and ensure a safe experience. This article will explore the forces, the differences between catamarans and monohulls, and various techniques to manage heeling effectively.

Key Takeaways

• Sailboat heeling is the leaning of a sailboat when it's under sail, resulting from wind pressure on the sails and resistance from the boat's keel.
• Heeling is a normal and necessary aspect of sailing, but excessive heeling can lead to loss of control and even capsizing.
• The optimal heel angle varies depending on the boat type and sailing conditions, but excessive heeling is generally considered to occur at an angle of 25 to 30 degrees or more.
• Techniques for managing heel angle include easing and reefing sails, adjusting the mast, changing course, and shifting crew weight.
• Catamaran and monohull boats have different heeling characteristics due to their design; catamarans have greater stability and less heeling, while monohulls rely on their keel's weight for counterbalance and require some heeling for optimal performance.
• Mastering advanced sailboat heeling techniques, such as weather helm, dynamic tuning, and sail twist, can help optimize boat performance while minimizing excessive heeling.
• Preventing capsizing and reducing heel involves monitoring wind conditions, adjusting sail trim and course, shifting crew weight, and knowing your boat's limitations.

Understanding Sailboat Heeling

Heeling is the term used to describe the sideways leaning of a sailboat when it’s under sail. This leaning happens because of two main forces: the wind blowing against the sails and the resistance of the sailboat’s keel pushing against the water.

Wind pressure: Wind creates a low-pressure area on the leeward side of the sail, generating lift and heeling force. The angle and shape of the sails play a crucial role. Sails with greater angles and fuller shapes generate more force from the wind.

Resistance from the keel: The keel acts as a counterbalance, pushing against the water and resisting the heeling force created by the wind.

The amount a sailing boat heels depends on several factors, including:

• Wind strength and direction
• Sail size and design
• Weight and distribution of people and gear on the boat

It’s important to remember that some heeling is normal and necessary for efficient sailing. However, an excessiveamount can lead to losing control and even capsizing. The maximum angle for most sailboats is between 20-30 degrees, although this can vary depending on boat design and conditions.

Optimal Heel Angle and Intentional Heeling

Intentional heeling.

Allowing a boat to heel to a certain angle will improve performance or speed. The hull shape can create a more efficient water flow, reducing drag and increasing forward motion. However, finding the right balance is essential, as an excessive amount can compromise safety and performance.

Catamaran vs. Monohull

Catamarans : These have two parallel hulls, which provide increased stability and a reduced risk of capsizing. They are designed to sail flatter than monohulls, with minimal heeling. Due to their wide beam and inherent stability, they can maintain high speeds without requiring significant angles.

Monohulls : These have a single hull and rely on their keel’s weight to counterbalance the force generated by the wind. Monohulls are designed to heel, and a certain amount is necessary for optimal performance. However, finding the right angle is crucial, as too much can decrease speed and stability.

Risks of Excessive Heeling

Allowing your boat to heel over 25 or 30 degrees can present risks to both safety and performance:

Safety risks : Excessive amounts can lead to a higher risk of capsizing, especially in monohull boats. Moreover, it can become difficult for the crew to move around safely.

Performance impact : When a boat heels excessively, its sail shape becomes distorted, reducing the sails’ efficiency and hindering forward motion. Additionally, a boat can lose its ability to steer effectively.

Techniques for Managing Heel Angle

Various techniques can be employed to control the heeling forces acting on the boat, particularly in gusty conditions. Some of the key strategies include:

• Easing the sails:  One of the primary methods of controlling the angle is easing the sails, which is particularly useful in gusty conditions. This involves letting out the control lines, such as the mainsheet or the jib sheet , to reduce the pressure from the wind. Easing helps lower the force, resulting in a more upright and stable boat.
• Adjusting the mast:  The mast can also be adjusted, especially in gusty conditions. For example, adjusting the rake (the angle at which the mast leans forward or aft) can influence balance. A more upright mast can help while being more raked can improve upwind performance. Mast bend can also be adjusted to flatten the mainsail, reducing the power and heeling force.
• Trimming the jib: By adjusting the sheet tension and position, you can balance the forces acting on the boat, ensuring it uses an optimal angle. Consider reducing the effect by using a smaller jib or reefing in strong winds.
• Changing course:  Steering the boat into the wind (heading up) or away from the wind (bearing away) can help. Heading up can depower the sails while bearing away can reduce the force by allowing the wind to flow more smoothly. However, some wind conditions can also increase heeling when heading upwind.
• Shifting crew weight:  Instruct your crew to move their weight to the windward side of the boat to counterbalance the force. This technique is especially effective on smaller boats, where the crew’s weight significantly impacts stability.
• Reefing:  In strong wind conditions, reefing (reducing their surface area) can effectively manage the situation.

Effects on Performance

Boat speed: Heeling affects boat speed, as the optimal angle between the wind and the sails changes with the boat’s inclination. Too much can cause the boat to lose speed, while the right angle can optimize the performance.

Sail shape: Changes in the sail shape and angle can affect the direction and performance. Proper sail trim is crucial to harness the wind efficiently and maintain control of the boat.

Crew position and movement: As the boat heels, crew members must adjust their weight and position using hiking straps or harnesses. The effects can make it difficult for them to move around the boat, impeding tasks such as trimming sails or handling lines.

Advanced Techniques

Weather helm technique: This method involves deliberately over-trimming the mainsail, causing the boat to tilt more to one side. By carefully managing this angle, sailors can achieve better upwind performance and control.

Dynamic tuning: This technique involves adjusting sail trim and crew weight while sailing to achieve optimal boat performance in different wind conditions. By responding to wind shifts and changes in boat speed, sailors can make continuous adjustments to maintain the desired angle.

Sail twist: Sail twist is the difference in angle between the top and bottom of the sail. By controlling sail twist, sailors can depower the sail when needed to reduce heeling forces while maintaining boat speed.

Masthead fly technique: Using a small wind indicator attached to the masthead, sailors can monitor wind direction and speed. This information helps sailors anticipate gusts and adjust sail trim and crew weight accordingly to maintain control and optimize boat performance.

How to Prevent Capsizing and Reducing Heel

Monitor wind conditions : Keep a close eye on the wind, as strong gusts or sudden changes in wind direction can cause excessive heeling. Adjust your sails and course accordingly to maintain a safe heeling angle.

Adjust sail trim : Proper sail trim is crucial in preventing capsizing. Ensure that your sails are set correctly for the current wind conditions. If your boat starts heeling too much, ease the sails or reef them if necessary.

Change course : Sometimes, turning into the wind (heading up) can help depower the sails and reduce heeling. Alternatively, you can bear away (turn downwind).

Shift crew weight : Instruct your crew to move to the windward side of the boat, using their body weight to counterbalance the heeling force. This can be particularly effective on smaller boats.

Practice active steering : Learn to steer your boat actively in response to changes in wind pressure. Feathering the boat into the wind during gusts can help maintain a consistent angle and reduce the risk.

Know your boat’s limitations : Understand the specific characteristics of your boat, such as its stability curve and maximum safe heeling angle. This knowledge will help you make informed decisions when managing heel and preventing capsizing.

Use appropriate gear : Ensure that you have the right equipment on board, such as lifejackets, harnesses, and tethers, to enhance safety during periods of excessive heeling.

The Role of the Rudder in Heeling

• Steering into the wind : When your boat starts to heel excessively, steer into the wind (heading up) to depower the sails and reduce the heeling force.
• Steering away from the wind : Bearing away (turning downwind) can also help manage the effect, allowing the wind to flow more smoothly over the sails, reducing the heeling force.
• Counteracting weather helm : In some cases, excessive heeling can cause weather helm , where the boat tends to turn and sail upwind on its own. Using the rudder to counteract this tendency helps maintain control and balance.
• Active steering : Develop the skill of active steering by responding to changes in wind pressure and adjusting the rudder accordingly. This helps keep a consistent heel angle and reduces the risk of capsizing.

Common Mistakes and How to Avoid Them

Over-heeling: Allowing the boat to heel excessively can lead to losing control and even capsizing. To prevent this, sailors should adjust sail trim and crew weight to maintain a safe angle.

Failing to anticipate gusts: Unexpected gusts can cause sudden increases in heeling forces. Sailors should closely monitor wind conditions, watch for signs of gusts, and be prepared to adjust sail trim and crew weight accordingly.

Improper sail trim: Poor sail trim can lead to excessive heeling and decreased boat performance. Sailors should regularly check and adjust the shape and angle of their sails to harness the wind effectively and maintain control of the boat.

Uneven weight distribution: Improper crew and gear weight distribution can cause the boat to heel more to one side, making it harder to control. Sailors should strive for even weight distribution and adjust to maintain balance and stability.

Ignoring weather forecasts: Keeping track of weather forecasts can help sailors anticipate changes in wind strength and direction, allowing them to adjust their strategies accordingly. Make a habit of checking the forecast before and during your trips.

Safety Considerations and Recognizing Excessive Heeling

While it can be an exhilarating experience, it’s essential to prioritize safety and recognize when your boat is heeling excessively. Excessive amounts can lead to an increased risk of capsizing, which could endanger the crew and potentially cause damage to the boat. 

Keeping the boat upright is one of the most critical aspects of managing heeling. Many sailboats are designed to naturally right themselves after a certain degree of heeling, thanks to the keel’s weight and the hull’s buoyancy. However, if a boat heels too far or too quickly, it may not have enough time or stability to right itself, leading to a capsize.

It’s essential to monitor the angle of heel and adjust your sailing techniques accordingly. While the best angle varies depending on the boat type and conditions, excessive heeling is generally considered to occur when the boat reaches an angle of 25 to 30 degrees or more. At this point, the risk of capsizing becomes significantly higher, and the yacht’s performance will likely suffer.

Monitor the wind conditions : Sudden gusts or strong winds can cause rapid, excessive heeling. Keep an eye on wind conditions and adjust your sails.

Adjust your sails : If your boat starts to heel excessively, ease or reef them to reduce the force of the wind on the sails.

Shift crew weight : Instruct the crew to move to the windward side of the boat to act as a counterbalance.

Change course : If necessary, turn the boat into the wind to depower the sails.

Understanding and managing sailboat heeling is crucial for safety and water performance. By recognizing the forces contributing, such as wind pressure on the sails and resistance from the keel, sailors can make informed decisions about sail trim, crew weight distribution, and course adjustments to maintain optimal heel angles.

It’s also essential to recognize the differences between catamaran and monohull boats and to be aware of the risks associated with excessive angles. By applying the techniques and strategies presented in this guide, sailors can develop the skills to control their vessel’s angle, enhance their boat’s performance, and ensure a safe experience for all on board.

Q: What is heeling?

A: Heeling refers to the leaning of a sailboat when it’s under sail, caused by the wind blowing against the sails and the resistance of the keel pushing against the water.

Q: What is the optimal heel angle?

A: The optimal angle depends on the type of boat and conditions. Generally, the maximum heeling angle for most sailboats is between 20-30 degrees. Excessive heeling occurs at angles of 25 to 30 degrees or more and can lead to a loss of control or capsizing.

Q: What are the main factors that influence a sailboat heeling?

A: The main factors are wind strength and direction, sail size and design, and the weight and distribution of people and gear on the boat.

Q: What are some techniques for managing heel angle?

A: Techniques include easing and reefing, adjusting the mast, changing course, and shifting crew weight. Advanced techniques involve weather helm , dynamic tuning, sail twist, and masthead fly techniques.

Ketch vs Yawl: Understanding the Differences

Storm sails for stormy seas, related posts, whisker pole sailing rig: techniques and tips, reefing a sail: a comprehensive guide, sail trim: speed, stability, and performance, leave a reply cancel reply.

Your email address will not be published. Required fields are marked *

• Cookie Policy
• Privacy Statement

© 2023 TIGERLILY GROUP LTD, 27 Old Gloucester Street, London, WC1N 3AX, UK. Registered Company in England & Wales. Company No. 14743614

Welcome Back!

Login to your account below

Remember Me

Retrieve your password

Please enter your username or email address to reset your password.

Add New Playlist

- Select Visibility - Public Private

• Yachting World
• Digital Edition

Sailing instrument calibration: How to set up your yacht for accurate readings

• July 20, 2020

A yacht’s instrument system can only be as good as the care with which it was set-up; ‘garbage in, garbage out’ is as true of a boat’s computer as any other, writes Mark Chisnell

Choose flat water and a quiet time of day for instrument calibration as you need to maintain consistent speeds and rate of turn under engine. Photo: Paul Wyeth

These tweaks will help make any integrated instrument system accurate and effective, whether the goal is to win races, or cruise efficiently, comfortably and safely.

The real key to setting up any instrument is careful calibration. I hate to say it, but this is one of the times when it’s worth reading the manual. It’s particularly important to approach sailing instrument calibration in a systematic order.

A lot of the data is interdependent, with much of the most useful information derived from the measurement of only five values: boat speed; compass heading; heel angle; apparent wind speed; and apparent wind angle.

It’s vital to calibrate these sensors first, and only when they are done accurately move onto whatever calibrations are provided for other functions like true wind speed and direction.

Compass set up and calibration

Electronic compasses will have the exact details of the best calibration routine described in their manuals, but it usually involves turning the boat in a circle or two. This allows the compass to calculate its own deviation curve and compensate for the local magnetic environment.

For example, to set up a Simrad Precision-9 compass requires the yacht to complete a 390° turn with a steady turn rate of 2°-3° per second. Once the turns are completed the compass applies the new deviation adjustment and sends a message that it’s finished.

There are a few things to watch out for in this process. It’s a lot easier and more accurate in flat, open water with no wind and no current because the turns need to be steady and even – so it won’t work if the yacht has to adjust course to avoid hitting something during the calibration.

Article continues below…

How new-age sailing autopilot systems are putting computers at the helm

A couple of decades ago I’d have recommended anyone planning an ocean crossing without a big crew to fit wind…

Can augmented reality really give us a vision of the future of sailing?

Google’s mission statement is ‘to organise the world’s information.’ This almost impossibly ambitious declaration of intent underpins the technology giant’s…

Check beforehand that there is no magnetic material anywhere near the compass sensor, with everything stowed in its normal sailing position. Beware of mobile phones in pockets of people sitting on deck, often right above the compass fitted below.

Once compass calibration is done, check the physical alignment of the instrument relative to the centreline of the boat by sailing down a known transit line. I also always check the boat compass against any hand bearing compasses on board – it’s useful to know if they disagree, because then a deviation card can be created for the difference.

Boat speed calibration should be one of the first jobs completed on any new boat, or at the beginning of a new season – particularly on a race boat. The helmsman and trimmers will get used to the setting, and it will be disruptive if the sensor has to subsequently be calibrated after a lot of sailing time.

Again, each individual system has its own calibration routines. The B&G H5000 has three variations. The first allows the navigator to compare directly with the GPS speed over the ground. This is only useful when there is absolutely no current.

Secondly, boat speed calibration can be manually adjusted as a percentage of a previous value. Or, for old school obsessives like myself, there’s a routine for correction against a measured mile.

Whatever system is used, some general rules can be followed to get a more accurate result. Set up when the water is flat; the logs measure the water flowing past it and are not too choosy whether the flow is created by the boat moving forward or up and down. If the boat is pitching it will record more distance than has actually been travelled.

Do the runs at fixed engine revs to keep the speed consistent. If using a measured mile, make sure the speed is the same at the beginning and end of every run – otherwise the acceleration will affect the results – so don’t slow the boat during the turn between runs.

Always steer as straight a line as possible between the chosen distance marks. If it is a proper measured mile then the chart will provide the bearings.

Any wavering from a straight line means the log will measure extra distance that will not be accounted for in the calibration calculation.

And finally, if the measured mile is in a tidal area then three runs are required to eliminate the tidal error and get an accurate calibration.

Apparent wind angle

The only real calibration possible for the apparent wind angle is symmetry on both tacks. The critical thing is to set this up on a day when there is very little or no wind sheer – usually a day with a well-mixed, gradient (not thermal or sea breeze) wind.

Apparent wind speed

It’s impossible to do much with this one, unless you’ve got access to a wind tunnel! If you have concerns ask the dealer or manufacturer, as they should be able to check the sensor.

On a calm day set the boat up with slack warps in the dock and put all the gear in its normal sailing position – including boom and spinnaker pole on the centre line. Whoever stays on board should also stand on the centreline while they read the heel meter.

Under these conditions the heel angle should read zero; if it does not then adjust it till it does, either with a software calibration or by physically moving the unit.

First published in the July 2019 edition of Yachting World.

• AROUND THE SAILING WORLD
• BOAT OF THE YEAR
• Email Newsletters
• Best Marine Electronics & Technology
• America’s Cup
• St. Petersburg
• Caribbean Championship
• Boating Safety

Steering Techniques For Different Winds

• By Steve Hunt
• Updated: October 12, 2021

It’s good to have rules of thumb to help you sail the boat as fast as possible in all conditions. Such guidelines can help the skipper drive their best and give the crew a common purpose in how they react to changes in wind. One distinction that can help you increase speed is to identify if you should be telltale or heel-angle sailing. In lighter winds, telltale sailing is appropriate—the skipper works hard to stream the telltales at all times for maximum speed, and the crew moves around to create perfect heel. In overpowered heel-angle ­sailing conditions, the skipper can steer much more freely, focusing on a consistent heel angle while the crew hikes hard. In light air, it’s all about maintaining speed; in breeze, it’s all about the heel angle.

Underpowered Conditions

Here, the crew controls heel angle and the skipper sails exclusively to the telltales. The goal is to stream the telltales, setting up the boat for maximum speed. The heel angle is totally on the crew, and it’s best if someone can communicate the power in the boat—maybe the skipper or mainsheet trimmer—to help coordinate the team’s movements. If it’s really light, you might be heeling the boat a little extra to leeward, and just how much needs to be communicated to the crew so the boat feels as good as possible.

In these light conditions, the jib trimmer should be to leeward playing the jib. If shifts come or the skipper needs to sail deeper to gain speed, the jib trimmer is right there to trim or ease, depending on the situation. The main goals the skipper is trying to achieve are sailing straight and keeping max speed. To allow that to happen, the crew moves to keep the heel angle perfect while the jib trimmer adjusts the jib.

For example, if there’s a wave set coming, the jib trimmer eases the jib while you bear off slightly. The bow down and coinciding jib ease keep the telltales streaming. The same thing happens if the boat suddenly slows—bow down and jib out to keep the telltales streaming. If the boat starts to feel great and the skipper can head up, the jib trimmer trims the jib with the turn to keep the telltales streaming perfectly.

Going straight, as opposed to heading up in a puff, or bearing off to pick up speed really connects the wind to the jib. Ideally, it never stalls. Some people call it “pressing” or “sailing fat” on the jib. Either way, you’re creating power, and that’s where the boat feels best. If the leeward telltales start to luff, the jib trimmer eases the jib a little to make the telltales stream rather than having you heading up. If you head up for heel-angle sailing in light winds, you end up pinching, and it really slows the boat. In a small puff, it’s much faster if the crew hikes against that power while you continue to sail straight.

During this light-air mode, the crew should be fully focused on moving around to keep the boat at the desired heel. When a puff hits, they should move to the high side quickly and smoothly to keep the heel perfect, and when the breeze dies, they should slide in. A slow-moving crew encourages the skipper to head up in puffs and bear away in lulls, which wastes power in puffs and height in lulls, and reduces speed. A ­well-coordinated team in light air is very fast—skipper sailing fast, jib trimmer working the jib, and crew super-concentrated on the perfect heel. Because it’s fast to have the jib trimmer play in the jib in lighter winds, the first person off the rail in a dying breeze should be the jib trimmer. They are much more effective to leeward, with a ­perfect view of the jib.

Building Breeze

Now the crew is starting to get up on the rail. They’re not yet fully hiking, but everyone’s on the high side. You trim the sails in a bit, the jib trimmer is on the high side, and the jib is cleated. The boat’s feeling pretty good. Now you can start sailing a little more to heel angle, which means steering up a bit in the puffs. The main trimmer is in the loop here as well, helping the skipper keep the boat at the correct angle of heel.

Keep in mind that, if there’s chop or waves, the boat is reaccelerating all the time, so you might not be able to pinch so much in the puffs in these conditions. You might be telltale sailing still if it’s real bumpy, so when you get a puff, the crew should hike and trimmers should ease the main or depower in some other way, depending on your boat—traveler down, backstay off, whatever you’re playing to keep the boat on its feet and keep speed through the chop.

In flat water, it’s fine to head up in the puffs a little to keep the heel angle down, raising the forward inside jib telltales to 45 degrees or so. As a rule, head up just enough for a little telltale lift when needed and encourage the crew to hike hard. Briefly pinching buys you time to depower and get the crew hiking, all the while ­keeping the heel angle perfect.

Overpowered Conditions

This is true heel-angle sailing. The breeze has built to the point where everyone’s fully hiked, and you’re easing the main or dropping the traveler to keep a constant angle of heel. The crew has essentially become ballast, and they are hiking as hard as they can. As long as the boat’s moving at a decent speed, you can head up as much as you need to keep the boat flat. In a big breeze, you might even luff a foot or two of the front of the jib when a big puff hits until you get sorted with easing the main, tightening the backstay or whatever you’re doing to depower. You’re going so fast and having so much power (too much) that sailing that high is fine.

A few years ago, when I was sailing my Etchells—just my third regatta after buying it—the breeze quickly increased, and we were overpowered. I headed up to keep the boat from heeling too much, bubbling the front 6 inches of the jib, and my main trimmer said, “Awesome mode! We’re flying!” And I was thinking, “What? I’m waiting for you guys to depower the boat so I can put the bow back down.” But I looked around, and we were higher and faster than everybody. We experimented with flattening the main and getting the bow down to stream the telltales, but it was not quite as good. That day we learned a new mode—that we could luff the jib in breeze and we’d go just fine. The main point here, though, is that in heel-angle sailing, the skipper should steer up to avoid heeling.

If it’s breezy but the water is flat, you can pinch a little more because there are no waves to slow the boat. If you’re sailing in waves and pressing on the telltales to go faster, constantly trying to accelerate, watch for flat spots. Every surfer will tell you that waves come in sets and in different shapes and sizes. Even on wavy and choppy days, there will be 5- to 15-meter ­circular spots that are pretty flat. Some sailors call them plateaus. If you enter a plateau and get a puff, try to feather or pinch. In general, you’ll probably be able to sail little higher than when in the bumps. Just before the waves return, drop the bow down, depower, and go for speed. In those conditions, you’re shifting back and forth between slightly bow down and true heel-angle sailing based on waves or flat spots.

The art of driving well comes after you understand everything we’ve been talking about, but then throw in the presence of shifts. Steering well suddenly becomes a moving target as you try to keep the boat at the perfect angle to the wind and coinciding perfect heel while the wind is shifting.

When that’s the case, here’s a good rule of thumb: If a puff is approaching from directly in front of you, it will most likely be a header. If it’s coming from your windward side over your shoulder, it’s most likely a lift. Knowing this can help you drive and trim the sails more accurately when they hit. The goals—maintaining a constant angle of heel and good speed—are the same, and if you can follow the shifts up and down while accomplishing that, you can really sail away from the fleet. For example, you get a nice-size puff that overpowers the boat. Normally during heel-angle sailing, you would head up to keep the heel the same. But if the puff is a header, you continue steering straight, the front of the jib bubbles, and everything works out fine. The shift helped you pinch without having to steer.

Conversely, again in a big breeze, you get a big puff, and it’s a lift. You understand that in overpowered conditions, a puff that’s also a lift is really going to knock you over. That’s because all of the sudden you are tight reaching, the opposite of pinching. It’s as if you bore away in a big puff, causing the boat to heel more. Rather than getting knocked over, good teams will “burp” the sails an extra amount right from the start, and the skipper will start heading up quickly and steer more than normal. That will help avoid the excess heel angle. At that moment, the main trimmer must ease the main a lot, and if the jib trimmer can ease the jib as well, or maybe the inhauler, even better.

On a J/70, for example, the jib trimmer might be inhauling the jib by bow-stringing the windward sheet on the high side, pulling the clew toward the mast. In that lift and puff, easing the windward sheet moves the jib trim-angle outboard, similar to easing the leeward sheet but better because the jib does not increase camber. It’s like dropping the main traveler—the whole sail barn-doors out while keeping the same shape and depowering the boat, and also opening the slot between the main and jib. Once back to a pinching angle, retrim the sails, and off you go having avoided excess heel.

In a blustery breeze, you can make big gains by balancing the concepts of sailing by the telltales and sailing by heel angle, knowing what your desired angle to the wind is and then factoring in lifts and headers along the way. The goal is to keep your boat in the best state possible, knowing that you’ll never be perfect all the time. As a skipper, when I head out for a race in shifty conditions, I think: “I’m going to try to keep my boat and sails at the perfect angle to the wind more than everyone else. And if I can do that a higher percentage of the time, I’ll probably be the fastest boat out there.” Keep in mind the two steering modes, and you can too.

• More: Boatspeed , How-To , print fall 2021 , sail trim
• More How To

The Wisdom of Augie Diaz

Why S-Turns, Roll Jibes and Roll Tacks Are Fast

The Path to Consistent Boatspeed

Headsail Trim Tips For Floating Leads

Anticipation and Temptation

America’s Offshore Couple

Jobson All-Star Juniors 2024: The Fast Generation

Wingfoiling Gear: A Beginner’s Guide

• Digital Edition
• Customer Service
• Privacy Policy
• Cruising World
• Sailing World
• Salt Water Sportsman
• Sport Fishing
• Wakeboarding

Yachting Monthly

• Digital edition

How to measure your yacht’s stability

• julianwolfram
• July 27, 2020

Naval architect Julian Wolfram uses some able hands, scales and maths to explain a practical way to calculate your boat's stability

Measuring, and then adjusting your yacht's stability can affect when you need to reef

Have you ever measured your yacht’s stability?

Adding heavy cruising gear will change your boat’s stability, so it is worth checking, although the names and terms, such as ‘Dellenbaugh angle’ and ‘metacentric height’, might be initially off-putting and leave you flummoxed.

These measures of a yacht’s stability or stiffness – used to compare one boat to another, or modifications that might have done on board – are more reliable than the crude and common ballast/displacement ratio, and understanding them will reveal the impact on your boat of all the additional cruising gear that has been added.

A simple spirit level can be used to conduct your stability experiment. Credit: Graham Snook

Ballast ratio is a flawed because it takes no account of the shape or depth of the keel, or of how heavily loaded the boat is.

Rather than ballast ratio, a better way to assess the stiffness is by dividing the position of her centre of gravity, as measured from the bottom of her keel (known as KG), by her draught, as this takes into account her both her draught and the centroid of ballast on board.

For any yacht built after 2002 the designer or builder will have calculated and potentially measured the KG for the minimum operating condition and probably for the fully loaded condition too.

You will need to induce at least 3° if heel for this to work. Credit: Graham Snook

This data is needed to do the required Recreational Craft Directive (RCD) calculations.

It may also be available for many yachts from before then if the builder or designer was conscientious.

Interestingly, this information has to be provided, by law, for a commercial vessel in the form of a stability booklet and there is no logical reason why it should be withheld from a yacht owner – but that doesn’t mean you’ll get it.

If you want to compare the stiffness of your yachts with others and can’t get hold of the KG, you will have to do an inclining experiment to calculate it.

Strips of wood are used to ensure accuracy. Credit: Graham Snook

An inclining experiment is required for all commercial vessels, including sailing yachts used for commercial purposes, charter and sail training, and is usually carried out, or at least witnessed by, a ship or yacht surveyor.

The inclining experiment yields the metacentric height (GM) which is a primary measure of stability.

Once you have GM then KG can be found using the hydrostatic particulars that are calculated from the table of offsets or the lines plan.

If you can’t get hold of these then you will have to get a 3D laser scan of the boat, when she is out of the water, and a naval architect who has a stability software package to do the calculations for you.

However, doing an inclining experiment is still worthwhile and, on traditional vessels built by eye or for which the lines and hull offsets have long since disappeared, it is the only option for assessing stability.

How to carry out an inclining experiment to check stability

Anyone can carry out an inclining experiment on their own yacht if they wish to check its stability.

It is done afloat, and simply involves moving weight from the centreline towards the deck edge and measuring how much the boat heels as a result.

The weights can be of any sort – jerry-cans full of water, baskets of old chain or the like.

Inclining weight(s) must be large enough to give at least 3° of heel – five large crew should be good for a 12m yacht, the smaller the boat, the fewer people are required. Credit: Graham Snook

I once did an inclining experiment on a 19m ferro-cement schooner with a weight that consisted of a bunch of students weighed on bathroom scales. It worked well.

Traditionally the angle of heel is measured using a pendulum (plumb line attached to a mast) and recording the offset to the side when the vessel heels.

The pendulum is usually damped using a bucket of water or oil.

Nowadays a device known as a stabilograph is often used which is more convenient.

Alternatively, I have used a long (1,830mm) spirit level successfully when the heel angle is between 3 and 6° and I think this is the cheapest and most practical way for a boat owner to give it a go.

Needless to say calm conditions are necessary to get an accurate measurement and mooring lines should be slack so the boat heels in a completely unrestricted manner.

Ideally the experiment should be done in the loaded condition but with the tanks no more than half full.

The crew are ideal inclining weights and six crew will weigh nearly half a ton (and maybe more in some cases!) and they don’t have to be lifted onto and across the boat.

Mark lines each side of and parallel to the centreline close to the deck edges.

Continues below…

What makes a boat seaworthy?

What characteristics make a yacht fit for purpose? Duncan Kent explores the meaning of 'seaworthy' and how hull design and…

Why you should regularly check your deck fittings

What’s really going on under your deck fittings? Ben Sutcliffe-Davies investigates the hidden weaknesses

How keel type affects performance

James Jermain looks at the main keel types, their typical performance and the pros and cons of each

The crew will stand facing the same direction with feet together, one foot either side of the line and their weight evenly distributed on both feet.

Ideally there should be one long line marked with chalk or tape on each side of the boat.

That may not be possible, however, and two or more lines may be needed; in which case you will have to note who stands where, as the product of each weight and its distance from the centreline is needed in the calculation.

Start by weighing each of the crew in turn on an accurate set of bathroom scales.

Then put the long spirit level across the cockpit with both ends supported so it is level.

Note the distance between the points of support (x mm).

You should be on the centreline when you are checking the level.

Get the crew on board and along the centreline to start with.

The heel of a yacht has historically been measured using a pendulum. Credit: Richard Langdon

Now get them all to take up positions on one side of the boat and carefully chock up the end of the spirit level so it becomes horizontal.

Pieces of plywood and plastic packers down to 1mm in thickness can be used as you need to measure to the nearest millimetre how much you have chocked up the end of the level (y mm).

Ideally the heel angle will be between 3 and 6° and you will have chocked up the end of the spirit level by at least 100mm.

Take the average of the values as the best estimate of GM. It should be accurate to 1 or 2%.

Typical values of GM range from about 0.8m for a 6m coastal cruiser rising to 1.5m or more for an ocean-going 12m yacht.

Read about what makes a boat seaworthy here

Wide hulls with little freeboard should have higher values; any significantly below this range should give cause for concern.

Knowing GM allows the Dellenbaugh angle, to be estimated.

The heeling arm is the distance between the centre of effort of the sail plan and the centre of lateral resistance of the hull and keel.

These can be estimated from a profile drawing, showing the keel and sail plan and worked out using known measurements.

Once calculated, for a 12m long boat a value of 12° would be considered stiff and 18° tender whereas for a 6m boat 18° would be considered stiff and 26 degrees quite tender.

For those who wish to learn more about this I recommend reading Principles of Yacht Design by Larsson, Eliasson and Orych.

How to measure the stability of your yacht

First you have to wait for Mother Nature to give you a calm day: any wind on the rigging could skew the measurements and drive you mad while you’re trying to get the level correct.

Also consider where you’ll do the test; while it is possible to do this on a mooring, the shelter of a marina is best for accurate results.

You will need to weigh crew to help with your calculations. Credit: Graham Snook

You’ll also need weight: passers-by, friends or relatives will do as long as they can spare you 10 minutes.

If not, jerry cans of spare fuel and water, sails, dinghy and liferaft will be needed.

The bigger the boat, the more weight you’ll need. You’ll also need a spirit level – the longer the better.

If it isn’t long enough to go across the cockpit seats of coaming, use a flat bit of wood long enough to span the gap.

1. Marking and measuring

You need to mark the centreline. Credit: Graham Snook

Marking the centreline on deck, we used masking tape, but a pencil or chalk line would do the trick. Then tape another line parallel to the centreline on deck, remembering to allow room for feet on the outside of the line.

Measure the distance from the centreline to the deck line. Use this measurement (d) to mark a second line on the opposite side. The last measurement you will need is the distance between the supports of your spirit level (x).

2. Prepare the weights

Weights need to be lined up along the centreline. Credit: Graham Snook

Next weigh your helpers or equipment to act as weights – a set of bathroom scales is ideal for this, whether for people or heavy objects. 
Slacken your mooring lines so they don’t affect the way your yacht heels.

Line your weights on the centreline mark and ensure the spirit level is showing your yacht is lying flat in the water. You have to remain on the centreline in the cockpit.

3. The experiment

You need to average the GM figures for both calculations. Credit: Graham Snook

Now move your crew or weights until they are over the deck line; people should stand with one foot either side of the line, weights should be piled up as best as possible. Now pack up the end of the spirit level to bring it level again, then take a note of the thickness of the packing to the nearest millimetre. Repeat the experiment with the weight on the opposite side. Finally, average the GM figures from both calculations.

For all the latest from the sailing world, follow our social media channels Facebook, Twitter and Instagram .

Have you thought about taking out a subscription to Yachting Monthly magazine?

Subscriptions are available in both print and digital editions through our official online shop Magazines Direct and all postage and delivery costs are included.

• Yachting Monthly is packed with all the information you need to help you get the most from your time on the water.
• Take your seamanship to the next level with tips, advice and skills from our expert skippers and sailors
• Impartial in-depth reviews of the latest yachts and equipment will ensure you buy the best whatever your budget
• If you are looking to cruise away with friends Yachting Monthly will give you plenty of ideas of where to sail and anchor

Caribbean Sailing School & RYA Training Centre

• RYA Instructors
• Sailing Yacht
• Grenada and the Grenadines
• Testimonials
• RYA Start Yachting
• RYA Competent Crew
• RYA Day Skipper
• RYA Coastal Skipper
• RYA Yachtmaster Preparation
• RYA Yachtmaster
• Mile Building Sailing Charters
• International Certificate of Competence
• RYA Essential Navigation and Seamanship
• RYA Day Skipper Theory
• RYA Coastal Skipper Theory / Yachtmaster Offshore
• RYA Yachtmaster Ocean Theory
• RYA Specialist Short Courses
• RYA Online Theory Courses
• RYA Start Powerboating Level 1
• RYA Powerboat Handling Level 2
• Course Schedule
• How To Get To Grenada
• Useful Links
• Caribbean Charters & Regattas
• Registration Form

Learning to Sail: Heeling Over

On the other hand, if you sail dinghies or other unballasted boats then you may capsize if you heel over. It’s part of the fun of sailing that type of boat! When you train to sail dinghies you learn how to quickly and easily right the boat. To start with, if you are slightly nervous, then we suggest learning to sail on a solid keel boat like Chao Lay .

Learning To Sail: What Does The Keel Do?

The keel is a flat blade that is attached to the bottom of the sailboat. It has two main purposes:

• It prevents the boat from being blown sideways by the wind, and
• It holds ballast that helps to keep the boat the right way round.

Be advised that you need to know the depth of your keel to safely navigate in shallow water.

Learning To Sail: Will We Capsize?

Keel boats have plenty of ballast to keep them upright, even in the most extreme conditions. All sailing boats will heel over, and you may even get a wave or two over the side. Don’t be alarmed as this is just part of sailing; keel boats are designed to heel and many skippers say it’s the most exciting part. Cleverly, keel boats were designed using basic physics:

• The ballast is located well below the waterline in the keel. If the boat heels over then the leverage increases. For example, you can compare this to holding a weight in your hand. As you raise your arm straight out from your body, the weight feels heavier the further your arm moves upwards. This is exactly the same as the ballast taking effect when a boat heels over.

It makes sense that a keel boat is very difficult to capsize when these two effects work together (reduced wind pressure on the sails and the ballast working to right the boat). Simply, trust the science and enjoy the experience!

Learning To Sail: How Far To Heel Over?

This is another question we get asked by students. Basically, you want the sailboat to move through the water as efficiently as possible. If you keep a steady heel angle, the blades and sails will efficiently glide through the flow of the water and wind. Keeping the angle consistent is important; there are three things you can adjust to ensure this:

• Sail trim, and
• Placement of weight.

The ideal heel angle is different for each boat. Generally, keel boats should be sailed somewhere in between 10 to 30 degrees.

Our next blog will look at sailing techniques used when  racing in regattas , taking an in-depth look at the three considerations listed above. Until then, check out these great books from the RYA:

Buy RYA Start to Race at the RYA Shop

• New Sailboats
• Sailboats 21-30ft
• Sailboats 31-35ft
• Sailboats 36-40ft
• Sailboats Over 40ft
• Sailboats Under 21feet
• used_sailboats
• Apps and Computer Programs
• Communications
• Fishfinders
• Handheld Electronics
• Plotters MFDS Rradar
• Wind, Speed & Depth Instruments
• Anchoring Mooring
• Running Rigging
• Sails Canvas
• Standing Rigging
• Diesel Engines
• Off Grid Energy
• Cleaning Waxing
• DIY Projects
• Repair, Tools & Materials
• Spare Parts
• Tools & Gadgets
• Cabin Comfort
• Ventilation
• Footwear Apparel
• Foul Weather Gear
• Mailport & PS Advisor
• Inside Practical Sailor Blog
• Activate My Web Access
• Reset Password
• Pay My Bill
• Customer Service

• Free Newsletter
• Give a Gift

How to Sell Your Boat

Cal 2-46: A Venerable Lapworth Design Brought Up to Date

Rhumb Lines: Show Highlights from Annapolis

Open Transom Pros and Cons

Leaping Into Lithium

The Importance of Sea State in Weather Planning

Do-it-yourself Electrical System Survey and Inspection

Install a Standalone Sounder Without Drilling

Rethinking MOB Prevention

Top-notch Wind Indicators

The Everlasting Multihull Trampoline

In Search of the Snag-free Clew

What’s Involved in Setting Up a Lithium Battery System?

Reducing Engine Room Noise

Breaking Point: What Can Go Wrong With Your Yanmar?

Mildew-resistant Caulks for Boats

Can We Trust Plastic Boat Parts?

Repairing Molded Plastics

Mailport: Marine plywood, fuel additives, through bolt options, winch handle holders

The Day Sailor’s First-Aid Kit

Choosing and Securing Seat Cushions

Cockpit Drains on Race Boats

Rhumb Lines: Livin’ the Wharf Rat Life

Safer Sailing: Add Leg Loops to Your Harness

Resurrecting Slippery Boat Shoes

Tricks and Tips to Forming Do-it-yourself Rigging Terminals

Marine Toilet Maintenance Tips

Learning to Live with Plastic Boat Bits

The Ultimate Guide to Caring for Clear Plastic

• Inside Practical Sailor
• Safety & Seamanship

Sailboat Stability Uncensored

The merits and limitations of the calculated gz curve..

At its most basic level, my goal as a sailor is pretty simple: keep my neck above water. Speed, comfort, progress toward a destination are nice, but if I need gills to achieve any of these, something is amiss. And since an upside-down boat tends to interfere with this modest ambition, I’d say our recent obsession with stability is justified.

This is far from our first foray into this topic. Shortly after the 1979 Fastnet race disaster , in which 15 sailors died, Practical Sailor embarked on a series of articles on sailboat stability. The racing rules of that era had resulted in designs that were quicker to capsize than their heavier, more conservatively proportioned predecessors, and we needed to explore why.

Since then, the lessons of Fastnet have been absorbed by the design community, culminating with the CE Category system and formulas used by various racing bodies like the Offshore Racing Congress to evaluate a boat’s fitness for the body of water where it will sail. But it’s clear that the tools we use to measure stability, and the standards we’ve established to prevent future incidents are still imperfect instruments, as we saw in the fatal WingNuts capsize in 2011 . And in the cruising community, where fully equipped ocean going boats hardly resemble the lightly loaded models used to calculate stability ratings, we worry that the picture of stability is again becoming blurred by design trends. This video gives some insight into the dockside measurement process for racing boats.

Last month, we examined multihull stability , including an analysis of several well publicized capsizes. One of the key takeaways from that report was the significant impact that hull shape and design can have on a multihull’s ability to stay upright. Another key observation was the distinction between trimarans and cats, and why lumping them together in a discussion of stability can lead to wrong conclusions. As we pointed out, many of the factors that determine a multihull’s ability are related to hull features—like wave-piercing bows—that are difficult to account for when we try to calculate stability.

This month, we take another look at monohull stability. This time it’s a formula-heavy attempt to tackle the conundrum that many cruising sailors face: How can I know if the recorded stability rating for my boat reflects the reality of my own boat? Or, if there is no stability rating from any of the databases, like the one at US Sailing, how do I assess my boat’s stability?

Stability Resources

If you are unfamiliar with this topic, I’d recommend reading three of our previous reports before digging into this month’s article. “ Dissecting the Art of Staying Upright ” and “ Breaking Down Performance ,” both by PS editor-at-large and safety expert Ralph Naranjo, take a broad view of sailboat design elements and how they applies to contemporary sailors. Nick Nicholson an America’s Cup admeasurer and former PS Editor, also offers a succinct discussion of stability in his article, “ In Search of Stability ,” which I recently resurrected from the archives. (Nick, by the way, is no relation to the current editor.)

When we’re talking about stability, the essential bit of information that every sailor should be familiar with is the GZ curve. This graphic illustration of stability highlights the boat’s maximum righting arm, the angle of heel at which resistance to capsize is greatest. It also illustrates the angle of vanishing stability (also called the limit of positive stability), the point at which the boat is just as likely to turn turtle as it is to return upright. Most boats built after 1998 have a GZ curve on file somewhere, and US Sailing keeps a database of hundreds of boats for members. As this month’s article points out, however, the published GZ curve does not always perfectly transfer to our own boats. Nevertheless, it is usually a good benchmark for assessing your boat’s stability ratio—not to be confused with capsize ratio the stability index or STIX .

For a succinct discussion of stability ratios (see below), Ocean Navigator’s excerpt from Nigel Calder’s Cruising Handbook lays good groundwork for the theory. If you really want to dive into the topic, Charlie Doane presents a good overview in this excerpt from his excellent book “ Modern Cruising Design .” Doane, like many marine journalists, relies greatly on the work of Dave Gerr , former director of the Westlawn Institute of Yacht Design and now a professor with SUNY Maritime Institute. Gerr’s four books “ Propeller Handbook ,” “ The Nature of Boats ,” “The Elements of Boat Strength,” and “Boat Mechanical Systems Handbook,” all published by McGraw Hill, illustrate Gerr’s rare talent for taking complicated topics and making them comprehensible and fun to read.

The GZ Curve

Shaped like an “S” on it’s side, the GZ curve illustrates righting lever. The high peak represents a boat’s maximum righting arm (maxRA), the point at which the forces keeping the boat upright (ballast, buoyancy) are strongest. The lowest valley, which dips into negative territory, represents the minimum righting arm (minRA), the point at which these forces are weakest. The curve also clearly delineates the limit of positive stability (LPS, also called the angle of vanishing stability), where the curve crosses into negative territory. Generally speaking, an offshore sailboat should have an LPS of 120 degrees or more. As Naranjo puts it, “It is this ability to recover from a deep capsize that’s like money in the bank to every offshore passagemaker.”

• Notice how lowering ballast lowers the center of gravity (CG) and increases a vessel’s limit of positive stability. In these examples, three identical 30 footers with the same amount of ballast, but differing keel stub depths, alter their draft and GZ curves. Boat 1 (5’ draft), Boat 2 (6’ draft) and Boat 3 (4’ draft). Note that Boat 3, the shoal draft option, has the lowest LPS and Boat 2, has the deepest draft, highest LPS and will sail to windward better than the other two boats. Editor’s note: One would think that with all the reporting we’ve done on stability, we’d be able to label a GZ curve correctly, but in the print version of the March 2021 issue we have mislabeled the curve. I apologize for the error. Sometimes, despite our best efforts, our own GZ curve turns turtle during deadline week. The correct version of the curve appears in the online issue and in the downloadable PDF. If you have questions or comments on boat stability, please feel free to contact me by email a [email protected], or feel free to comment below.

RELATED ARTICLES MORE FROM AUTHOR

17 comments.

Thanks for this reminder, another error has crept into the diagrams I think. The yacht seems to have 2 CBs and no GG.

I noticed that also, Halam. With no center of gravity and all buoyancy that boat will never sink. Of course, it could be at rest upside down also.

The link to the US Sailing database is pointing to a different place than I think you intended. It is not the database of boats, but rather information on curve calculation and definitions.

Hi Darrell, sorry to be the bearer of a correction, but it looks like the CG is labeled as CB in the first graphic.

As far as I know, a rule of thumb is that a sail boat can tolerate cross breaking waves not higher than her max beam. Is it true?

It often amuses me to see the many crew sitting out on the gunwale of a keel boat, (monohull) as the righting effect must shorely be minimal. Especially when compared to a small racing trimaran. It does help the ‘Gyration’ as shown in the Fastnet tragedy. Even the ‘Skiffs’ have ‘racks’ out the side, & I’ve seen all sorts of ‘keel arrangements’. They just haven’t put ‘floats’ on the end yet. I’d love to see someone do a ‘stability kidney’, as Lock Crowther said (all those years ago), the the righting, (capsizing force is 35? degrees off the bow. Thought provoking? not antaganistic. Keep up the good work, and thanks ‘B J’.

A useful view of stability is to consider where the energy to resist capsize is stored. As a boat rolls, the center of gravity is also raised with respect to the center of buoyancy, so the weight of the boat is lifted, at least through some angle (as long as the GZ is positive) and energy is stored as a lifted weight. This means that a stability incident is exactly equivalent to rolling a ball up a hill; it will always roll back down until it passes over the top of the hill. This is why most commercial and military stability standards use “righting energy” for at least one criteria. The ISO 12217-1 standard for coastwise and oceangoing power boats requires at least a minimum absolute energy and an energy ratio exceeding a nominal overturning energy of combined wind and wave (similar to the IMO standards for cargo ships and 46 CFR 28.500 for fishing vessels).

Can anyone comment on the stability of Volvo Ocean Race boats? While various mishaps have occurred over the years, I don’t believe any of them have capsized and remained inverted. VOR boats are nothing like the Pacific Seacraft and similar designs from more than 50 years ago, yet they seem “safe”.

Does anyone know why? Size, keel depth and weight, modern design tools?

Good and useful article, particularly to someone considering buying a new or used sailboat. As an add-on to the effect of draft, I would add that most, if not all, builders increase the weight of the keel to try to compensate for the reduction of righting moment with the reduction in draft. I recommend to readers Roger Marshall’s outstanding book entitled “The Complete Guide to Choosing a Cruising Sailboat”. Chapter 3 “Seaworthiness” and chapter 10 “Putting it All Together” are worth the cost of the book many times over. Unfortunately the book is getting out of date, it was published in 1999 and many newer sailboats have come on the market.

Mark, thank you for recommending to read Roger Marshall’s book.

May i suggest reading the book, “Seaworthiness the forgotten Factor”. The author (C.J.Marchaj) makes a number of interesting observations about modern boat design (published in ’86, so not that modern). What sticks with me is the notion that one aspect of seaworthiness is how well a person can survive inside the boat in question– deeper keels make for more righting moment but also a snappy roll, for example, promoting incapacitating seasickness. The boat has to be well enough behaved to “look after” the crew.

My boat 40 ft Samson SeaFarer ketch is fairly tender initially but then settles down once the rail is int he water….but I have never had the top of the mast in the water to see if it would recover well. Since I am not and engineer or math whiz (and don’t want to be!) I wonder if there is a practical way to actually test the stability while on the water. Is there a way for example to pull the top of the mast down to varying degrees/angles and measure the force it takes to do it and use that as a guide to stability. Could that provide some extrapolative certainty to going further around the wheel of misfortune? Crossing between NZ and Australia (45 years ago..) we were knocked over (not my current boat) with the top third of the mast in the water and she righted very quickly (very comforting) – no great mishap except to make the cook go wash the soup out of his hair and confirm all the things we hadn’t tied down…including dishevelled crew.

Cheers Gerry

Can someone please link to the article referenced above on multihull stability? I’ve searched, but cannot find it. Thank you kindly!

I have the same inquiry as Jet. I can’t find the Multihull article. Please advise ASAP!

The link in the 4th paragraph works for me:

https://www.practical-sailor.com/sailboat-reviews/multihull-capsize-risk-check

Couldn’t find this link either. Thanks.

Is it possible to get a link to the USSailing boat database, or some hints on where to find it on the site? The current link just goes to ussailing.org.

LEAVE A REPLY Cancel reply

Log in to leave a comment

Latest Videos

Island Packet 370: What You Should Know | Boat Review

How To Make Starlink Better On Your Boat | Interview

Catalina 380: What You Should Know | Boat Review

• Privacy Policy
• Do Not Sell My Personal Information
• Online Account Activation
• Privacy Manager

M.B. Marsh Design

Understanding monohull sailboat stability curves.

One of the first questions people ask when they discover I mess around with boat designs is: "How do you know it will float?"

Well, making it float is just Archimedes' principle of buoyancy, which we all know about from elementary school: A floating boat displaces water equal to its own weight, and the water pushes upward on the boat with a force equal to its weight. What people usually mean when they ask "How do you know it will float" is really "How do you know it will float upright?"

That's a little bit more complicated, but it's something every skipper and potential boat buyer should understand, at least conceptually. (Warning: High school mathematics is necessary for today's article.)

A yacht at an angle of heel

Let's consider a boat at rest, sitting level in calm water. The boat's mass is centred on a point G, the centre of gravity, and we can think of the force of gravity as acting straight down through this point. The centroid of the boat's underwater volume is called B, the centre of buoyancy. The force of buoyancy is directed straight up through this point.

We now heel the boat over by an angle "phi". Point G doesn't move, but point B does: by heeling the boat, we've lifted her windward side out of the water and immersed her leeward side. The centre of buoyancy, B, therefore shifts to leeward.

The force of buoyancy, acting upward through B, is now offset from the force of gravity, acting downward through G. The perpendicular distance between these two forces, which by convention we call GZ, can be thought of as the length of the lever that the buoyancy force is using to try to bring the boat upright. GZ is the "righting arm".

If we draw a line straight upward from B, it will intersect the ship's centreline at a point called M, known as the "metacentre". (Strictly speaking, the term "metacentre" applies only when phi is very tiny, but a pseudo-metacentre exists at any given angle of heel.) The metacentric height is a useful quantity to know when calculating changes in trim and heel.

(Can't see the images? Click here for now , then go update your web browser.)

We can easily draw a few conclusions simply by looking at the geometry:

• The boat will be harder to heel, i.e. more stable, if GZ is increased.
• Lowering the centre of gravity, G, will increase GZ.
• Moving the heeled centre of buoyancy to leeward will increase GZ.
• If GZ changes direction- i.e. if Z is to the left of G- the lever arm will help to capsize the boat instead of righting it.

Stability Curves: GZ at all angles of heel

To prepare a stability curve, the designer must find GZ for each angle of heel. To do this, she must compute the location of B at each angle of heel, and determine the height of G above the base of the keel (the distance KG).

In the early 20th century, finding B at each angle of heel was an extremely tedious process involving a lot of trial-and-error, a lot of calculus, and days or weeks of an engineer's time. Today, this can be computerized, and takes only a few seconds once the hull is modelled in a CAD program. Finding KG, though, is still a tedious process: it can either be measured by moving weights around on an existing boat and measuring the resulting angle of heel, or it can be calculated by tallying up every piece of structure, ballast, equipment and cargo on the boat.

Once that math is done, the designer can plot GZ (or righting moment, i.e. displacement times GZ) over all possible angles of heel. This produces the familar stability curve:

All yacht skippers should be at least somewhat familiar with their own boat's stability curve, and it's a useful thing to study when buying a boat. To read the curve, we look at the following features:

• The slope of the curve at low angles of heel tells us whether the boat is tender (shallow slope) or stiff (steep slope).
• The righting moment at 15 to 30 degrees of heel tells us about the boat's sail-carrying power. A large righting moment indicates a boat that can fly a lot of sail; a boat with a lower righting moment will need her sails reefed down earlier.
• The maximum righting arm (or righting moment), and the heel angle at that point, tells us where the boat will be fighting her hardest to get back upright. If this is at a low angle of heel, we have a boat with high initial stability- she'll feel very stable under normal conditions, but a bit touchy at her limits, and relies on her skipper's skill to avoid knock-downs. If the maximum righting arm occurs at a very large angle of heel, the designer chose to emphasize ultimate stability- she'll be hard to capsize, but will heel more than you might expect in normal sailing.
• The angle of vanishing stability is the point where the boat says "Meh, I'm done" and stops trying to right herself. Looking at the diagram above, this means that Z is now at the same point as G. A larger AVS indicates a boat that's harder to capsize.
• The region of positive stability is the region in which the boat will try to right herself. The integral of the righting moment curve (i.e. the area of the green region) is an indicator of how much energy is needed to capsize her.
• In the region of negative stability , the boat will give up and roll on her back, her keel pointing skyward. The integral of this region (i.e. the blue area) tells us how much energy it'll take to right her from a capsize; if this area is relatively small, the waves that helped capsize her might have enough energy to bring her back upright.

Try it on a real boat

How does this apply to some real boats? Let's consider a 10 metre, 8 tonne double-ender yacht of fairly typical layout and proportions. The parent hull looks something like this:

Keeping her draught (1.5 m), displacement (8 tonnes), length (10 m), freeboard, deckhouse shape, etc. the same, we'll adjust the shape of the midship section to yield four boats that are directly comparable in all respects except beam and section shape. Hull A is a deep "plank on edge" style , hulls B and C are moderate cruising yacht shapes, and the wide, shallow-bilged hull D resembles an old sandbagger - or a modern racing sloop.

Now, assuming that G lies on the waterline (so KG = 1.5 m), we can compute the righting arm GZ as a function of the heel angle. If we multiply the righting arm GZ by the displacement, we get the righting moment.

Some immediate observations from this graph:

• The narrow hull "A" has relatively little sail-carrying power at low angles of heel, but will self-right from any capsize. Her good "ultimate stability" comes from using ballast to get G as low as possible.
• The wide hull "D" can fly a lot more sail, but if she goes over, she ain't coming back up. She gets her high "initial stability" from her wide beam, which moves the heeled centre of buoyancy farther to leeward.

There's a problem, though: We've assumed an identical centre of gravity for all four boats. That's not realistic. The deep, narrow hull will have her engine and tanks low in the bilge; the wide hull must mount these heavy components higher up. Let's reduce hull A's KG measurement to 1.35 m, and increase hull D's KG measurement to 1.65 m, a more realistic value. We'll scale KG for the other two accordingly.

The overall conclusions don't change much, but we now have some realistic numbers to play with.

• Hull A, the narrow one, will have a hard time flying much sail. She'll heel way over in a breeze. But she can't get stuck upside down.
• Hull B, a moderately slender cruising shape, also can't get stuck upside down- her AVS is 170 degrees. Her extra beam causes the centre of buoyancy to move farther to leeward when she heels, so she has more initial / form stability than hull A and can carry more sail.
• Hull C, which is typical of modern cruising yachts, has over twice the sail-carrying power of the slender hull A. She'll heel less, and since her midship section is much larger, she'll have more space for accommodations. The penalty is an AVS of 130 degrees. That's high enough that she can't be knocked down by wind alone, but wind plus a breaking wave- such as in a broach situation - could leave the boat upside down until a sufficiently large wave comes along.
• Hull D, the broad-beamed flyer, can hoist more than three times the sail of hull A at the same angle of heel. She'll be quite a sight on the race course with all that canvas flying. Her maximum righting moment, though, is only 37% more than hull A's, which leaves less of a margin for error- hull D is more likely to get caught with too much sail up, and will reach zero stability at a lower angle of heel. If she does go over, she has considerable negative stability, making it unlikely that she'll get back upright.

Work to capsize

If you're one of that slim percentage who paid attention in high school physics, you're probably looking at those curves and thinking: "Force (or moment) as a function of distance (or angle).... hey, if you integrate that, you get the work done !

And so you do, with the caveat that we're using a static approximation to a dynamic situation. The results are valid for comparison, but the actual numbers may not mean very much.

Let's do that for each of our hulls. We'll integrate the righting moment curve as a function of heel angle, up to the angle of vanishing stability, to get the work done to capsize the boat. We'll also integrate from the AVS to 180 degrees to get the work done to right the boat from a capsize.

Our four boats require roughly the same work to capsize! Changing the shape of the midsection affected the shape of the stability curve- a wider boat had more initial stability and less ultimate stability. In this case, though, our vessels are all about the same size and require about the same amount of work to capsize.

Righting from a capsize is another matter. The narrow, deep hulls A and B will self-right without any outside influence- a nice confidence-booster if you're heading into the open ocean, although the reduced sail-carrying power and limited interior space of these vessels will probably be more important to most skippers.

The moderate cruising hull, C, needs a bit of help to self-right, but any combination of wind and waves that can do 95 kN.m.rad of work on the boat is likely to produce a wave that can do 10 kN.m.rad of work on that same boat.

Our broad-beamed racer, hull D, is not so fortunate. Righting her from a capsize takes one-third the work that capsizing her in the first place did, and her acres of canvas were probably a major factor in the initial capsize- they're now underwater, damping her roll motion instead of catching the wind. The odds are that this boat will stay upside-down until someone comes along with a tugboat or crane.

Lessons Learned

What's the take-home message from all this?

If you're buying a new boat: Look at her stability curve, and compare it to other boats.

• Good: Large region of positive stability, small region of negative stability, high angle of vanishing stability, steep slope at low heel angles.
• Iffy: Shallow slope at low heel angles (makes it hard to fly lots of sail, excessive heeling when underway).
• Risky: Low angle of vanishing stability, large region of negative stability.

If you already have a boat:

• If you know her point of maximum stability, you can be sure to reef the sails well before  that point.
• If you know her AVS and the shape of the curve in that region, then when a broach or knockdown happens, you already know how hard she'll fight to come back upright.
• If you know how much area is covered by the negative stability region of the curve, you'll have some idea of whether she'll come back from a capsize on her own or else have to wait for help.
• Determine if anything you've changed- a dinghy added on the deck, perhaps- has moved the centre of gravity.
• If G has moved, adjust your mental model of the stability curve accordingly: just shift the curve up or down by (change in height KG) * sin(heel angle).

Confounding Factors

What we've discussed here is just about how to read the stability curve- it's not a complete picture.

There are many other factors that must be considered to get a complete understanding of a boat's stability. Among them:

• Dynamic effects. Everything discussed so far is for the static case, and is good for comparison purposes. But in practice, boats move.
• Waves. Stability curves are calculated for flat water, ignoring the effect of waves.
• Differences in rigging. Weight aloft has a much larger effect on the boat than weight down low- particularly where the roll moment of inertia, an important property for dynamic stability, is concerned.
• Keel shape. Keels tend to damp rolling motion; this behaviour is quite different with a long keel than with a fin keel, or with a fin keel underway versus a fin keel at rest.
• Downflooding. Everything we've discussed here assumes that the boat is watertight in any position. If she takes on water when rolled, everything changes.
• Cockpits. Our demonstration boat doesn't have a cockpit. A large cockpit could hold several tonnes of water- and with a free surface, no less. That means that G will move all over the place, usually in the wrong direction.

Further Reading

Steve Dashew's article " Evaluating Stability and Capsize Risks For Yachts ", and others on his site, discuss stability-related risks as they relate to cruising yachts.

Technically-minded readers should refer to a naval architecture textbook, of which my present favourite is Larsson & Eliasson "Principles of Yacht Design" (McGraw-Hill).

Don't even think about buying a cruising yacht without first reading John Harries' extensive series of articles on boat and gear selection .

Topic: 

• Boat Design

Boats: 

Great stuff.

A really great piece, thank you. You have the very unusual gift of being able to make complex issues easy to understand.

Other confounding factors

One major confounding factor which most English-speaking designers still seem to routinely dismiss, or overlook, is to do with the nature of knockdown lever moments in a 'survival storm' situation:

You specifically state you're not taking waves into account, so this is addressed at those who do, in the conventional way -- generally led by the insights of academics and researchers tracing their conceptual methodology back to the likes of Marchaj.

The lever moments I'm thinking of arise from the vertical offset between: Where the wave force vector acts, and Where the hull resistance vector is located.

It has long been contended by the school of expedition yacht designers, going back to around the days of Damien II, from France in the 70s, that the greatest risk ... and arguably the only one worth worrying about for such vessels ... was due to the tripping moment caused by the vertical offset between the centre of effort of a true breaking wave, and the centre of resistance of the hull AND UNDERWATER APPENDAGES

When a large ocean wave breaks entirely forwards, the part which was formerly the crest avalanches down the front of the wave. Admittedly this behaviour is VERY rare offshore - where almost all 'breakers' actually spill most of the water down the back, but it's these events which present a real survival threat, and which define the limits to a vessel's capability.

Unlike the water particles in the body of the wave, which are circulating in the well known way of text book diagrams, and effectively not going anywhere over time, this "former crest" water has escaped from the wave system and is travelling rapidly under the influence of gravity down a steep ramp whose geometry (as opposed to constituent particles), in the case of a Southern Ocean wave of truly heroic proportions, might itself be advancing as fast as 30 to 40 knots.

So we have an aerated but still rather massive entity tumbling down above this already very fast moving ramp, hitting the topsides and cabin coamings, in the worst case, perpendicularly.

The contention of the French school was that, in this situation, while a high freeboard is clearly undesirable, the absolute last thing you want, which trumps everything else, is deep appendages providing lots of lateral grip, situated down in green water. This would provide a lever arm converting the sideways impulse (which is at a height not very far from the centre of mass, and hence not inherently an insuperable problem) into a very dangerous overturning moment.

The insight was based on simple empirical observations, such as of a flat wooden plank, or a surfboard with no appendages, floating side on to breaking waves at a surf beach. Despite having no ballast whatsoever, and a zero GZ in the plank case, this will sideslip down those waves and stay happily the same way up, in conditions where (say) a windsurf board with a deep centreboard (whether ballasted or not) will be tumbled repeatedly.

They reasoned that the thing to avoid at all costs, for a well found expedition yacht, was a knockdown with an angular acceleration sufficient to snap the rig.

This turned everything on its head with regard to the conventions of stability calculations: the relative positions of the centre of mass and the centre of buoyancy become largely irrelevant: the former should if anything ideally be high, so the vector from the striking crest passes through or near it, (to minimise the inertial overturning moment) while the latter is almost irrelevant because on the face of such a steep wave, the hull is in virtual freefall, and the hull is largely disengaged from green water. Aerated water offers little buoyancy.

This is so divorced from statics (which are arguably most useful for calculating how to prevent ships capsizing at a dock) that it is a shame to see so much reliance on static measures persisting to this day, in educating sailors, defining ultimate seaworthiness, and framing regulations and recommendations.

Be that as it may: this insight led to a completely different school of storm management by the adventurous people who sailed off to places like the subAntarctic and Antarctic in the new generation of beamy, generally low-freeboard # hulls, equipped with swing (or even dagger) ballasted keels capable of retracting - in many cases - right within the canoe body.

# ideally, no cabin trunk - which on the face of it is bad for self-righting...

In survival conditions, these sailors began retracting these keels, even though on the face of static stability calcs, this is entirely wrong. And (AFAIK*) not one of these yachts has yet been lost in the deep south, despite them making up the majority of the fleet, and I'm not even aware of a single 180deg knockdown to such a vessel configured in this way.

There have been, and continue to be, numerous knockdowns and dismastings of fixed-keel yachts designed to the other, older paradigm.

*(The first two losses of private expedition yachts in Antarctic waters both occurred within the last two years, and neither was a vessel of this type)

So even if these sailors are not right, they're clearly not VERY wrong.

Re: Other confounding factors

You are quite correct that when you are facing breaking waves, static stability analysis is not going to show the whole picture. Being caught in large breakers is certainly one of the highest-risk situations a yacht can face.

The "let it slide sideways" approach can have considerable merit in such a situation, if the boat is designed with this in mind. On a monohull sailing vessel, this calls for a retractable keel and a canoe body with relatively little lateral resistance of its own. If you do this, of course, you also have to ensure that the vessel won't trip over the leeward gunwale when she's surfing sideways with the keel retracted. There are plenty of good, seaworthy vessels out there with such a configuration.

The price you pay for doing it that way is that it's harder to right the boat if she does capsize. Frankly, though, I would rather not capsize in a non-self-righting boat than be upside-down in one that will eventually get herself back up. There are tens of thousands of catamaran sailors out there who would seem to agree.

This is not to say that static stability traits are not important: they certainly are. Given two vessels of generally similar configuration, the stability curves will tell you quite a lot about what kind of behaviour can be expected from each.

Static stability curves are certainly not the whole picture. There are several important dynamic aspects- the lateral resistance effects and the roll moment of inertia, among other features- that can have a huge effect in extreme situations. I'll discuss these in more detail in future posts.

I am thinking about. Buying a

I am thinking about. Buying a 38 foot guimond lobster boat. I am thinking Of widening the stern to 10 feet from 8 ft 8 in. Also I want to add some fiberglass to the keel to make her a little deeper maybe 36 in from present 32 inches. Should I make the new hull water line 90 degrees? Will this be better than a round traditional edge? Should I add bilge keel fins for more stability?

Modifying a design

The kind of modifications you're describing are fairly extensive. You would be wise to arrange a meeting with a naval architect, or with a builder who has extensive experience with that type of boat. With the boat's drawings and a good description of what performance characteristics you want, the professional will be able to assess what modifications (if any) would be appropriate- or if you'd be better off choosing a different design from the start.

Stabilty of Twin Keel Monohulls (Bilge Keel)

Wondering about the stability of bilge keeled sailboats, specifically the Snapdragon 26. How does a second keel affect relative stability of this kind of vessel? Any thoughts appreciated.

Static stability is determined by the hull shape and by the distribution of mass, i.e. the centre of gravity. Two identical hulls, one with a single fin and one with twin keels, will have approximately the same stability curve if they have the same centre of gravity. The twin keel configuration is usually chosen to allow shallower draught, though, so the centre of gravity will often be higher than for a single-fin boat.

There is a significant performance sacrifice with this configuration. A higher centre of gravity reduces the sail-carrying ability, the lower aspect ratio foils are not as efficient to windward, and the extra wetted surface increases drag. The flip side is that you can safely dry out at low tide in places where most monohulls would never be able to go.

Ultimately, though, the keel configuration is a fundamental part of a design, and there's no real answer to "How does a second keel affect stability". It's the performance of the entire boat that matters, and unless you have two boats that are identical except for keel configuration, it doesn't make much sense to separate out this one aspect of the design. The class's performance record and the experiences of skippers who have sailed that class in bad weather are better ways to assess the relative seaworthiness of an existing design.

Stability Curves for Hunter 34

I'm french and it's not that easy for me to understand all of this but here is my question:

Do you know who I can contact to know the stability curves of my sailboat. It's a Hunter Sloop 34' 1985

I asked directly at Marlow-Hunter, they said they don't have this information.

Someone told me that Hunter Manufacturer has it and that I can have it for some dollars but it seems that this is not the case.

Can you help me?

Tracking down data for old boats

Danielle, if I'm not mistaken, that Hunter would be one of Cortland Steck's designs. There's a chance that he might have the data you're looking for.

Stability curves are incredibly tedious to calculate without a computer, though, so many- if not most- boats designed prior to the advent of modern 3D CAD never had one calculated at all. It's possible to build a computer model of an existing boat and calculate the required data, but for most practical purposes you can find the important information through an inclining experiment. This essentially consists of moving known weights around the boat and measuring how she heels in various load conditions, and it's one of the more common ways of measuring stability data for an existing vessel in commercial service where all of these details must, by law, be properly measured and documented.

Righting a Capsized Vanguard Nomad 17

I read on the web that it takes 420 lbs of crew weight to right a capsized Nomad. Is that true? I weigh 135 lbs and I sail single-handed. It's now November and the water is getting too cold to find out.

Re: Righting a Capsized Vanguard Nomad 17

Gerardo, A 625 pound boat with a beam of 8 feet is not going to be an easy thing to right. You might find Sailing World's article on the boat interesting. They were advised by the manufacturer's rep that the boat can't be righted by one person in the way that you'd right something small like a Laser. But if you flood the tank (through the spinnaker well) on one side, you'll be able to roll her far enough to pull her back up like a dinghy, and then drain the tank again. I agree that you would NOT want to test this in November!

37 Foot Sailboat

I am from the Maldives in the Indian Ocean. I am building a fiberglass sailing yacht using local boat builders. Its 37 feet and 11 feet with a long keel of 3 foot deep. And will use concrete in the keel. They will be putting 9 fiberglass mats. Interior and the bulkheads will be done using marine plywood. The hull is going to look more like a Fisher 37. And the cabins like a Nauticat. I am intending to use ketch style two masts. I was surfing the internet and am trying to understand what are the issues that I need to take into consideration. Your explanations is very helpful. I am just wondering whether you will comfortable if I communicate on this topic. Thanking you.

Re: 37 Foot Sailboat

Ahmed, it's good to have you here and feel free to chime in on relevant threads, or to contact me directly. It's always neat to see what everyone else is building.

Help with stability estimate

Matt, I found your article very informative, good stuff! Where might you think my vessel Crusoe might fit A thru D.
 57' O.L. 13' beam-25 tons-4.5 ton ballast lifting keel. Here is the vessel:
 
 http://yachthub.com/list/yachts-for-sale/used/sail-monohulls/pilothouse-... 
 thanks,
 
 Thomas

To summarize, in very general terms: Category A is an offshore-capable yacht. Category B is a coastal cruising vessel, able to handle weather at sea but not recommended for extended offshore use. Category C is a short-range inshore vessel that is expected to take shelter rather than facing a storm out in the open. Category D is a small, fair-weather vessel such as a skiff or dinghy. The static stability properties are the main factor that determine which category a particular boat design is intended to fall in. But, in addition, the builder must comply with dozens of requirements for structural integrity, watertightness, emergency equipment, etc. for the boat to actually fall in that category. It's quite possible for a boat designed for Category A to end up being a Category B vessel because of corner-cutting during the build.

Assessing Southerlies and Tayanas

Would you care to give an opinion on the Southerly Yachts with retractible keels and twin rudders, also on Tayanas as to seaworthiness and construction. Thank you

Southerly & Tayana

I don't have first-hand experience with either of these marques, so I'm afraid I can't offer much that's meaningful.

Southerly tends to have a fairly good reputation. You do pay a fairly substantial premium for the complicated retracting keel, but there are some cruising grounds where the only options are a retractable keel or a multihull.

The Tayana line has produced a mix of models from several different designers, some very traditional, rugged and slow, others relatively modern. I'd have to know exactly which one you have in mind to say much more than that.

Your best bet for meaningful data on either line would be to prowl some forums looking for the owner's club for each marque. Yacht owners generally love to talk about their yachts, and if you're patient, you can usually find most or all of a particular model's weak spots by asking owners how they handle rough weather and what they've had to fix or replace so far.

I really enjoyed your article

I really enjoyed your article. I'm trying to make a stability model myself and I was interesting in the equations you used to find GZ as a function of heel angle and then how you found the displacement. I'm also interested in how you calculated the different curves for the different hull designs. Any pointers would be greatly appreciated. Thanks!

I'm not sure if I mentioned

I'm not sure if I mentioned it in my last comment, but I'd also like the equations for getting the displacement you multiplied GZ by. Thanks!

Sources for calculations

Hi Cole, Finding the displacement from the lines is pretty easy. If it's a CAD model, just find the volume; if it's a 2D drawing, find the area of each of the stations and use Simpson's rule to integrate over the waterline length. Finding G is just a matter of adding up the weights and moments for every component of the ship - each frame, the hull planking, the engine, each piece of hardware, and so on. Finding GZ for a given heel angle is relatively tedious, but it's essentially the same procedure (find the station areas, integrate over the waterline length, find the station centroids, weight the centroid offsets by station area to find the CB). There is an iterative step here as you must adjust the waterline position to make the displacement the same as in the at-rest case. For practical purposes, though, virtually everyone computes their stability curves using a proven software tool like Orca3D or ArchimedesMB. The actual calculations are described in detail in most good yacht design textbooks, eg. Larsson & Eliasson's "Principles of Yacht Design".

Stability of Chinese Junk Hull

Hi Matt, Your article is very informative. I am studying the feasibility of building a wooden ocean going Chinese Junk. History recorded that there were huge junks sailing 600 years ago in Zhenghe's days. The latest record for a large junk sailing across oceans is the Keying which sailed from Hong Kong to New York and London in 1848. She is 160ft LOA, 33ft BEAM and 13ft (rudder up) 23ft (rudder down) DRAFT, 700-800 ton DISPLACEMENT. As it is too difficult to re-build a wooden junk of such size, I am studying the record of fishing junks built about 30 years ago. A junk capable of sailing in force 8 wind. She is 23m(75.4ft)LOA, 5.66m BEAM, 1.69m(DRAFT), 1.2m(FREEBOARD), 138000kg (DISPLACEMENT). There is a dagger board extending 2.5m from the bottom, located about 1/3 waterline from the bow in front of the main mast. The rudder can be raised in shallow water. It is perforated with an area of 6.7sq.meter. The bottom is almost flat. The design of junks were evolved from generations of experience without scientific verification. I am surprised that the length and beam is so close to Volvo 65, but the displacement is 10 times those of Volvo. I am wondering if a flat bottomed boat is stable in rough ocean condition until I read the comment by Andrew Troup in 2012 about a boat without appendages can surf safely on the steep slope of the waves. I am glad if you can shine some light on the stability of traditional Chinese junks. John Kwong

Chinese Junk

A hundred and thirty-eight tonnes on 23m LOA? Yowzah, that's quite the boat. There's nothing fundamentally wrong with a relatively flat bottomed shape, or with retractable appendages. The risk of a flat bottom is more to do with slamming and pounding, which is much less of a problem in a heavy boat. Before investing hundreds of thousands of dollars in such a boat today, it would certainly be prudent to have the design drawn up and analyzed with modern software tools. There are certainly improvements from the last 50 years that could be applied to a much older design. A six-century pedigree is nothing to sneer at, though, and the fundamental design - updated with some modern construction techniques and with the added confidence of a full stability analysis - might still be a good one.

Relative locations of G and B

Hi Matthew. Thanks for such an interesting and informative article. Most diagrams show B below G so I guess this must be the most usual arrangement. However, I wondered if there might be a class of yacht (lightweight but with deep bulb keel) where G moved below B. I guess this would give a very good static G-Z curve (but I note also the comments made by Andrew (above) re dynamic stability that this might not be the best design to go winter sailing in the Southern Ocean!)

Monocat Hull

Matt what would you think this Monocat 50 Hull Form (see link)? Its a very different design- Monohull at the Bow, Catamaran at the Stern, 2x Lift Keels, One Ballasted, the other Forward non ballasted dagger board. I just cannot find information on it anywhere? I'd assume it would have similar characteristics to a very beamy monohull and thus would not self-right from a knockdown!? This is what im wanting to find out, will it self-right & is it safe offshore? Mashford Monocat 50 15.24m LOA 5m Beam 3Ton Ballested Lift Keel 0.8m - 2.1m

(there is a cad drawing of its underwater hull design in this advert) NB: Unfortunately your Spam Filter will not let me paste the link, but if you search the internet for MASHFORD MONOCAT it comes up for sale everywhere.

Ive been trying to locate the Designer Chris Mashford with no luck? feel free to email me too any info, cheers. Mal

Mashford Monocat

I'm not too familiar with the Monocat. My educated guess would be that stability-wise, it'll be much like a "skimming dish" racer - very stiff and powerful at first, hairy at the edge, and not self-righting. I'd have to sail one to be sure, but I have a suspicion that it could have the worst of both worlds - the relatively high drag and the ballast burden of a mono, with the complexity and high sailing loads of a cat. The main appeal seems to be the huge living space in a relatively modest beam, suggesting it's meant for short-term coastal cruises and charter work. Reliable reports on them seem to be very hard to come by, I suspect they weren't built in large numbers.

Great article! Thanks. My question is on actual statistics of vessels that have actually capsized. Understanding that this would likely be under reported, it would seem fruitful ground to examine questions of which static or dynamic factors pan out and are predictive for hulls that ended up upside down, and the stories behind them?

Does such a database exist?

reason for knowing the departure gm

Sorry I am bringing in a different topic entirely . pls I have read most of your articles and I have found them to be very useful . Pls I really want to know the importance of knowing your departure gm before commencing on a voyage... thank you

downflooding

Hi Matthew - I was reading your blog just now on Aug 23. I wanted to know how intake of 450l water affected the stability of a 9000kg / 41ft sailing yacht that I was skippering in a force 9 storm around Dover on Aug 3rd 2017. We encountered rather high waves of estimated 7m and had 52 kts apparent wind, which may have been the beginning of a force 10, because we did only 4kts through the water under storm jib and 3x reefed main. Once safely parked in Dover, we pumped 450l water out of the boat. Floorboards were floating... Any idea how that amount of water may have affected stability?

Kind regards

Martin Lossie

Calculating a stability curve

You mentioned calculating stability curves is tedious, and mostly done with CAD these days. I'm a new owner of a 1969 Columbia 26 Mk II and would love to understand the stability curve for my boat. A few enterprising owners have rescued the blueprints of this boat and placed them online, so I have the measurements available. Are there folks out there willing to do the CAD work to create the curve? Otherwise, what would be the easiest way for me to get one created for my boat?

Thanks for a GREAT article explaining this concept!

Add new comment

More information about text formats

Filtered HTML

• Web page addresses and e-mail addresses turn into links automatically.
• Allowed HTML tags: <a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd>
• Lines and paragraphs break automatically.
• No HTML tags allowed.

Or, by topic:

• Log in using OpenID
• Cancel OpenID login
• Request new password

Attainable Adventure Cruising

The Offshore Voyaging Reference Site

Sail Heel Angle

The late, great—I know it’s a cliché but he was— Buddy Melges , when asked how to drive a boat well upwind, would say that the secret is keeping the angle between the headstay and horizon constant.

For us lesser helmspersons, an inclinometer makes this way easier.

I was just about to fit one to our J/109 when I realized that the smart compass I installed last winter also measures heel angle and sends that out on the NMEA 2000 network, so it was just a matter of moments to add it to one of the cockpit readouts.

Once the boat is fully powered up, sailing a constant heel angle through the puffs and lulls is a way faster and more comfortable way to helm upwind than just following the jib telltails.

Excessive heel is also a not-so-subtle hint that it’s time to reef.

Nothing more than 20 degrees is fast on the J/109 , flatter with a full crew on the rail.

The M&R 56 is fastest up wind at about 23-25.

Boats that are not as easily driven will need more heel, and full-keel boats with a lot of wetted surface are often fastest at high angles—as much as 35 degrees.

That said, many people, particularly those new to sailing, let the boat heel too much.

Anyway, every sailboat should have a way to display heel angle. If your autopilot compass does not have this feature, a simple inclinometer will do .

sailing skills

Please Share

I have always spelled it “heel”, and merriam-webster seems to agree with that spelling. is heal a common spelling in the northeast?

No it’s a common spelling among dyslexics, of which I’m one! I will change it, thanks.

20 degrees is about right for modern, beamy boats, I’ve found. Once past that the underwater shape starts to tell and not in a good way. Reef early, reef often!

Good point, although the J/109 is not that beamy, and neither is the M&R 56, at least by modern standards, so I think a lot of being able to sail well at low heal angles is about keel efficiency and keeping drag low.

I was thinking about buying one of these https://www.airmar.com/Catalog/Marine/GPS-Heading-Sensors/GH2183

It outputs pitch and roll to the network so I guess you could read the roll as heel angle?

That sounds right, but I don’t know for sure. You will also want to make sure you can read that out on whatever MFD you have.

Agree that heel angle readout is great, as is rudder angle. Your compass should have trim too which is interesting both for long term and short term fore/aft weight distribution. Obviously the boot stripe will help with the former.

Great article. Key is knowing your boat. Learned very early back at summer camp sailing lasers as a kid it may seem faster sailing with the rails in the water but the leeway increases and your added rudder to over come weather helm slows your actual over ground speed. Same can apply to those rule bending IOR boats with big over hangs designed to heel early will sail faster as the water line increases as they heel but the optimal angle range is narrow as weather helm will increase and then leeway and drag starts to slow you down again. (Not to mention risk of a broach)

• Forums New posts Unanswered threads Register Top Posts Email
• What's new New posts New Posts (legacy) Latest activity New media
• Media New media New comments
• Boat Info Downloads Weekly Quiz Topic FAQ 10000boatnames.com
• Classifieds Sell Your Boat Used Gear for Sale
• Parts General Marine Parts Hunter Beneteau Catalina MacGregor Oday
• Help Terms of Use Monday Mail Subscribe Monday Mail Unsubscribe

Heeling Explained

• Thread starter Don Guillette
• Start date Jul 29, 2012
• Featured Contributors
• Sail Trim with Don Guillette

Don Guillette

One of the sail trim forum listers, Robert Lang, sent me this info, which I thought mates would find interesting -- especially RichH and Joe from San Diego both of whom might be related to Robert (just kidding!!). What do you two guys think of his explanation?? Good day to you and thanks for all the tips you provide to us, including to me in particular in past e-mails. Now, I saw your post where you said "I don't know how heeling effects the speed of all boats but I do know the Catalina 30 and the Catalina 25 and those boats sails the fastest (for me) at about 20 to 25 degrees of heel." I can explain it and do so in a manner that you can see. I assume that you know that a symetric foil will create lift if the angle of attack is not directly and perfectly on its center line. You can show that by drawing a symetrical foil (plan view, not elevation), place a dot near but not on the centerline, and then measure the distance from the dot to the rearmost portion of the foil. One route will be longer than the other. Two particle parting at the point of the dot MUST come back together at the same time at the end of their trip. The longer side will have a greater flow and the greater flow will have less pressure, thus causing lift to that side. Now, ask, what has more force, air at ST&P at 1 MPH or water at 1 MPH? Water being denser has more mass and thus has more force at the same speed. So, given all other things equal, the same foil in water will create MORE lift than the same foil in air. Infact, the difference in lift is INCREDIBLE -- HUGE -- most notable. Becuae the difference in lift is so huge, where a small change in a foil's shape may create a rather insignificant change in lift, a small shange of the foils shape may create a significant change in the lift in water. Now, get some three by five cards and a cup of coffee or hot cocoa. Make yourself a nice foil shape out of a card. Keeping the top, create a foil. Keeping it level, dip it in the coffee. It will leave a stain where the level line is. Cut the foil apart from its centerline fron to centerline rear point. Measure the left and right lines. If it is symetric and level, the lines will be equal. Now, build a similar symetric foil from another card. Dip it into the coffee gain but this time, pretend that you are heeling 15 to 20 degrees. Now, cut apart the foil and measure the left and right lines. The lower line will be, relative to the upper line, shorter. Heeling the boat causes the symetric foil to become an asymtric foil and you need just a bit of change to have a lot of lift. Now, as you continue to heel, at some point you interrupt the flow over the keel. Intterupted flow provides NO lift. And it is as you start to pass 20 or 25 dgrees that you lose lift, and speed, and control. You actually stall the foil. That is why some heeling makes you faster while too much (see my avatar) hurts you even as it thrills the crew). ____________________________________________________________  

While heeling can increase the speed of some sailoat designs.... I would suggest that an increase in waterline length is the major reason...... not an increase in lift from the keel. The fin keel provides lift when the boat doesn't move exactly straight ahead (crabbing, if you will) changing the angle of attack due to side pressure from the sails... the benoulli effect seems plausible here... but... is it a result of heeling the boat????? well, uh, Don... you're article hasn't exactly convinced me after I did some quick research on the subject and couldn't find anything to support the premise. The consensus was that lift from the keel was a result of its angle of attack from the boat's slightly sideways motion through the water.... and that heeling changed a boat's hull from symetric at the waterline, to a more asymetric shape which would induce lift. Also, in an attempt to circumvent class restrictions, some sailboat's designs incorporated large overhanging bow and stern portions that extended waterline length, and thus potential top speed, when the vessel was heeling....Think 12 meter AC boats.  

Sam Salter said: The bit about 2 particles having to arrive at the trailing edge together isn't true! One particle is going to be long gone when the other gets there. There is no physical reason they have to arrive together. While the bit about the heeled keel sounds plausible (It's late at night and I'm having trouble seeing it in my mind) wouldn't that just give you lift to windward. I'm not seeing any force to give you extra speed? sam Click to expand

A never ending argument! But my 2 cents...doesn't the foil created by the sails also lose lift as you get closer and closer to the water, as you are not only trying to make the air flow take a longer path, thereby increasing speed but now you are compressing the air flow against the water? Think of a boat heeled at 88 degrees(theoretically). If you took a very thin piece of wood (think rectangle here) and measured the force it takes to move it thru the water at say speed X, if you "heeled" it 10 degrees I don't think the force needed to move it a speed X would be any different. The next time your boat is out of the water take a string and measure the difference from the normal waterline and a 20 degree heeled waterline, which I think would be longer. I agree with Joe, it's about boat shape. I also agree with weinie!!!!  

anchorclanker

In physics, as well as proven in the wind tunnel by the Wright Brothers, regarding an airfoil in laminar flow, or in our case a hydrofoil or sail, the flow striking the leading edge and separating to follow both sides of the foil WILL arrive at the trailing edge at the same time. It is because of this that true lift exists at all. On a symmetrical or non symmetrical foil, as the angle of attack changes, flow is altered because the leading edge has changed angle of incidence, forcing the fluid over the two surfaces to take longer and shorter tracks. The fluid taking the longer course over the foil creates a lower pressure than the fluid taking the shorter track, and that force acts to pull the foil in the direction of lower pressure. In fact it was the Wright Brothers we owe for discovering those properties, that allow us to fly, have efficient props, and teach us how sails really work. It is not the same as dragging a block of wood with squared off edges through the water or air. A foil will have laminar flow until it reaches the critical angle of attack where flow begins to separate away from the longer surface, eddies begin to form, drag climbs higher, and the foil stalls. It should also be pointed out that propellers work the same way. They dont push air or water like a fan, but rather pull via the properties of a proper foil. When a prop stalls, in water the pressure will drop so low on the face as to cause the water to boil, and then we have Cavitation, which should never be confused with Ventilation (air being drawn down into the prop from the surface) Cavitation can destroy a prop by eroding the face. I believe whats being pointed out in the OP, is that as the boat heels over, a greater angle of attack is taking place along the keel, as well as the rudder, in an attempt to keep the boat pointed. That greater angle of attack is creating greater drag, slowing the boat, while simultaneously the sails lifting force (vector) starts to point downwards rather than forwards. Therefore, as soon as the boat begins to lose forward velocity, the drag has exceeded the forward lifting force. Just as in an airplanes wing, the same four forces are in effect. Force over drag, lift over gravity.  

Scott T-Bird

Theories abound! ... But I have some simpler thoughts. First of all, hull speed is related to the length of the wave that is created. It's a chord length between waves (the longer the wave length, the greater speed potential of the boat). Any increase in speed due to increasing the length between waves is a result of the boat squatting in the water either when heeled or even squatting when reaching or running. It is the squatting that increases the CHORD of the waterline length, not the heeling. I don't think it is related to the increased length due to curvature of the hull. If that were the case, then all beamy boats would be inherently faster, but they aren't (necessarily). I assume we are talking strictly about boat speed and not VMG, because VMG is a separate discussion where the hull shape and heeling probably does have a beneficial effect. I'll get into that later. I was reminded last week (when I was struggling to find a spot on the lake that had some wind), that my boat is faster when reaching. I happened to be on a reach when I finally found a slot that gave me some consistent wind and my boat leaped into a speed that was significantly higher than I can achieve when beating into the wind. With balance and sail trim in good form, I had at most 10 to 15 degrees heel with apparent wind at about 12 knots a little bit aft of beam. At this point of sail, the boat isn't heeling but it is squatting and the sails are standing nice and tall to take full advantage of the wind. Of course I had a full main and a 150 genny pulling with all it had. At this point, I could safely say that my boat was performing at hull speed and probably a little more. If I had turned around to beat into the wind, apparent wind would have been in the neighborhood of 20 and I would have had more than I want to handle with a full main and 150 genny. I would have trimmed sails to try to maintain heel between 20 to 25 degrees and would probably have been making way at half a knot slower in boat speed compared to my reach. If I had trimmed sails for more power (raised the traveller car) I would probably heel excessively (25+) and with frequent round-ups, the boat speed would slow down significantly. IF I was able to reduce sail to the perfect sail plan where I was able to maximize power and maintain the optimum heel for a balanced helm I doubt that I could achieve the same boat speed that I had on a reach. This is where I agree with people who say that flatter is faster. But it is really just a function of maximizing power from the wind at an angle of heel that is managable. It seems obvious to me that the greater power from the wind you can harness (that includes trimming to allow your boat to sail on her feet), the more speed you will achieve until limiting factors such as displacement hull speed, and losing control of the helm with excessive heel, either limit your speed or slow you down. When you are beating into the wind with perfect sail trim, but the boat is heeled only 15 degrees, you are not reaching your potential speed for the simple reason that there isn't enough wind to power your sail plan. It seems obvious to me that with more wind, you would harness more speed and heel more. It has very little to do with increasing your water line length or anything hull-shape related. I agree that hull shape does affect lift, which helps improve VMG to windward. The curvature of the hull shape does cause a boat to climb to windward when heeled to leeward. Windsurfers know that when sailing a board at slow speed (in displacement mode), pressuring the leeward rail makes the board point. The curvature of the board, or the rocker, is the reason for this. A sailboat behaves similarly.  

Re: Theories abound! ... Airplane wing, curve on top. Sailboat wing, curve on bottom more or less. Boat slipping sideways tripping over keel makes mast lean over. It works fine for my understanding level, all I gotta do is make the telltales fly. All U Get  

anchorclanker said: In physics, as well as proven in the wind tunnel by the Wright Brothers, regarding an airfoil in laminar flow, or in our case a hydrofoil or sail, the flow striking the leading edge and separating to follow both sides of the foil WILL arrive at the trailing edge at the same time. Click to expand

simple answer I am assuming that if the boat is not healing to the point where part of the keel is out of the water (much more than 20 degrees) than there is no effect of air foil on the keel. The dominant effect would be the righting moment caused by the sails being more and more off the vertical centerline of the boat. As the center of effort of the sails move away from the vertical centre of effort in the keel, this creats a turning moment to turn the boat to windward. This is what causes weather helm in a boat that is otherwise balanced in its sailplan when the boat is not healing. The more healing there is, the more the rudder has to dig into the water to keep the boat on course and this creats drag in the water. Heal is inevitable as the sail catches the wind but too much heal means too much drag from the rudder. Therefore, it is possible that in heavier winds, a reefed sail can actually give the same or even higher boat speed with less heel. Would this simple answer make more sense than the air foil? Oliver....  

Ross, do you attribute the lifting of a wing (airplane, keel, rudder, sail) to Newton's third law of motion over the more common explanation of the bernoulli effect?  

Oliverhg said: I am assuming that if the boat is not healing to the point where part of the keel is out of the water (much more than 20 degrees) than there is no effect of air foil on the keel. The dominant effect would be the righting moment caused by the sails being more and more off the vertical centerline of the boat. As the center of effort of the sails move away from the vertical centre of effort in the keel, this creats a turning moment to turn the boat to windward. This is what causes weather helm in a boat that is otherwise balanced in its sailplan when the boat is not healing. The more healing there is, the more the rudder has to dig into the water to keep the boat on course and this creats drag in the water. Heal is inevitable as the sail catches the wind but too much heal means too much drag from the rudder. Therefore, it is possible that in heavier winds, a reefed sail can actually give the same or even higher boat speed with less heel. Would this simple answer make more sense than the air foil? Oliver.... Click to expand

Stu Jackson

Ross S said: If this were the case then ask yourself how any plane can fly upside down? In fact, this has nothing to do with how a plane flies at all. Click to expand

Stu Jackson said: Heal - to feel better Heel - the back of your shoe or boat tilt Click to expand

Well, we heard from Joe from San Diego. Now we need RichH to chime in. This discussion is way to deep for a common seaman like me. All I was repeating about the keel and rudder was what Buddy Melges told me in a San Diego bar about 100 years ago.  

Oliverhg said: I am assuming that if the boat is not healing to the point where part of the keel is out of the water (much more than 20 degrees) than there is no effect of air foil on the keel. The more healing there is, the more the rudder has to dig into the water to keep the boat on course and this creats drag in the water. Would this simple answer make more sense than the air foil? Oliver.... Click to expand

LaColla said: Ross, do you attribute the lifting of a wing (airplane, keel, rudder, sail) to Newton's third law of motion over the more common explanation of the bernoulli effect? Click to expand

Ross, thanks for your remarkably understandable explanation. As interesting as the physics are, I think it is equally interesting that there is uncertainty in the explanation of exactly how a foil works, especially given how much they are used in aviation, sailing, wind generators, ect. For instance, those that I have read that use Newton to explain lift use you first example as evidence for it- that you in fact don't need a curved surface of a wing to generate link-think of the balsa wood airplanes with the flat wings by way of example. Anyway, I find the topic fascinating and I'm really amazed to see that not everyone agrees on exactly how a wing works.  

LaColla said: Ross, thanks for your remarkably understandable explanation. As interesting as the physics are, I think it is equally interesting that there is uncertainty in the explanation of exactly how a foil works, especially given how much they are used in aviation, sailing, wind generators, ect. For instance, those that I have read that use Newton to explain lift use you first example as evidence for it- that you in fact don't need a curved surface of a wing to generate link-think of the balsa wood airplanes with the flat wings by way of example. Anyway, I find the topic fascinating and I'm really amazed to see that not everyone agrees on exactly how a wing works. Click to expand

• This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. By continuing to use this site, you are consenting to our use of cookies. Accept Learn more…

As fears of war brew, China and Taiwan are still joining forces to rescue lost fishermen, Taipei says

• Taiwan and China authorities are still working together on at least one front: coast guard rescue.
• Taiwan's coast guard has helped China with 17 rescues in the last three years, the agency's chief said.
• Both coast guards launched a joint operation to search for Chinese fishermen on Thursday.

Taiwan's coast guard has run more than a dozen joint rescue operations with China in the last three years, the agency's chief said on Thursday — marking a rare area of cooperation between both governments amid mounting tensions.

Chou Mei-wu, the director-general of Taiwan's coast guard, made the comment in parliament on the same day that his agency announced one such joint effort.

Taiwan's coast guard said it's working with Chinese authorities to rescue crew from a Chinese fishing boat that capsized early Thursday morning near the Kinmen Islands.

The boat was carrying six crew, two of whom were found dead while another two were rescued, Taiwan's coast guard said.

Taiwan dispatched four vessels and China sent six to search for the remaining pair, per the agency.

"In the last three years, we had 17 such cases where they asked us for support, and we rescued 119 people," Chou told legislators.

Related stories

The joint rescue comes as Beijing's posture toward Taiwan — which it says falls under China's jurisdiction — grows increasingly hostile. Chinese leader Xi Jinping has vowed that reunification is "inevitable," and hasn't ruled out using force to take the self-governed island.

Taiwan in January re-elected the Democratic Progressive Party, which aims to resist Beijing, indicating growing island-wide resentment toward absorption by the mainland.

Despite the tensions, China remains one of Taiwan's most important trade partners, with Taiwanese investments in the mainland totaling $203 billion in the last two decades . But cross-strait investments have fallen to 20-year lows as the threat of war looms and US-China tech disputes rise.

Indeed, Chou revealed the statistics on coast guard cooperation at a four-hour parliamentary hearing discussing the Chinese Communist Party's "normalized intrusion and threats" to Taiwan.

Meanwhile, some on Chinese social media treated the recent joint effort as a sign of Taiwan becoming more subservient to mainland rule. Yet many also expressed unhappiness that the incident was portrayed as Taiwan helping China, and therefore taking the lead.

In February, tensions flared again when a Chinese fishing boat carrying four people capsized in the Taiwan Strait while being pursued by Taiwan's coast guard.

Two of those on board died, while Taiwan temporarily detained the other two.

Taiwan's coast guard said the boat lost balance on a sharp turn. However, China has accused Taipei of lying after one of the fishermen claimed to state media that the coast guard rammed his vessel.

Watch: China shows how it would attack Taiwan as tensions rise

• Main content