sailboat capsize formula

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What is a Sailboat Capsize Ratio and how to measure it

Aug 05, 2020

less than a min

As a boat owner, there are many formulas and ratios that you should know about. Do not worry if you are new to the whole marine and naval realm, however. There is always time to learn more if you are willing to. Here is a summary of what a sailboat capsize ratio is. 

A sailboat capsizes ratio is a parameter used to show whether a boat can recover from an inverted, capsized position or not. This term was mainly developed after the Fastnet race disaster . This was a 1979 race where a storm destroyed several yachts during the last day of the race, also causing 19 victims. Since then, tank tests have been developed to offer a prediction on how likely is a boat to recover after capsizing. 

The capsize ratio is a good indicator of what the boat is designed for. For example, if a boat has been designed to be used at sea, then it will have been equipped with features to make it more stable and prevent it from flipping over or capsizing. The capsize screen in this case can have a value below 2. 

A capsize of over 2 does not necessarily mean a bad thing. Boats with such a capsize value are better for coastal cruising as they offer higher form stability and a larger interior. In addition, these boats sail closer to the shore which allows them to return to safety in no time in case of a disaster.

How to measure the sailboat capsize ratio

There are several online calculators that can help you figure out your sailboat’s capsize ratio . These calculators are based on the capsize screening formula defined as below:

Capsize Screening Formula = Beam / ((Displacement/64.2)1/3)

The displacement in this formula is measured in pounds . This formula does not take into consideration the location of the ballast or the shape of the hull. In terms of understanding the value here’s the gist. The lower the value, the less likely is the sailboat considered to capsize. If the value is 2, then the boat is still accepted to take part in races, although this might depend on the race committee. 

The sailboat capsize ratio is also related to the displacement and beam. Therefore, two sailboats can have the same value if they also have the same displacement and beam. Their stability however could differ although they have the same capsize value. 

All in all, the sailboat capsize ratio is more important when related to racing sailboats used further from the shore. This parameter is not a crucial one to take into consideration when analyzing a chartered yacht or any sailboat intended for pleasure. 

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What Is Capsize Ratio And How Is It Calculated?

With so many different terms and calculations in the sailing world, it’s no wonder that capsize ratio is confusing.

Have you ever been on a boat and had it suddenly turn over? Or maybe you’ve seen a boat capsizing on TV. Either way, it’s not a pretty sight and you might be eager to know your boats capsize screening ratio before you head out for a sail.

But what exactly is a capsize screening and how is it calculated? Keep reading to find out.

Table Of Contents

What is capsize ratio, how to calculate capsize ratio.

• What’s A Good Capsize Screening?
• Why Is Capsize Ratio Important?

Capsize Ratio Calculator

Capsize ratio is a term used to describe the likelihood of a sailboat recovering after it has capsized. It gives an indicator as to whether or not the boat will right itself after being fully inverted.

This term was developed after the tragic  Fastnet race disaster in 1979, where a storm destroyed several yachts and caused 19 deaths at sea on the last day of the race.

After this disaster, tests were done to try and determine a calculation that could be used to determine a boat’s ability to right itself after capsizing, and therefore give an indication of whether or not it is suitable for offshore sailing.

You can calculate the capsize screening of your boat yourself using a simple formula.

To calculate the capsizing volume using this formula, you need to know several key variables about your boat: The displacement in pounds and waterline beam.

Once you have these values, you can use a simple equation to determine your capsizing volume in tons as well as your capsize ratio.

Capsize Screening Formula = Beam / ((Displacement/64.2)1/3)

This formula doesn’t factor in the location of the ballast and there forefore the centre of gravity, or the shape of the hull. It also doesn’t take into consideration things like weather conditions which can play a significant part in whether your boat will right itself or not.

What Is A Good Capsize Screening Ratio?

There isn’t really a good or bad figure, they just mean slightly different things which we’ll cover more below.

The way the calculation works, is that the lower the value, the less likely a boat is to capsize. The cut off for many offshore races is a ratio of 2 or under, indicating that boats with a ratio over 2 are more likely to capsize.

While calculating your boats overall capsize ratio may seem like a complex task, it’s an important indicator in determining whether or not your boat is suitable for offshore sailing. It’s a great tool to use before setting off on your next adventure.

Why Is Capsize Screening Important?

Unless you plan on long, offshore passages, capsize ratio isn’t actually that important.

It simply gives a rough indication of whether or not your boat was intended for offshore use where you’re more likely to encounter the kind of waves that might cause a capsize.

A beamy design with a capsize screen over 2 has some real advantages for coastal cruising:

– Higher form stability, supporting more sail as winds move up to 20 knots.

– More interior room for living aboard.

Coastal cruisers can usually return to port before conditions build breaking waves tall enough to capsize the boat.

If you’re not great at maths like me, or you want to calculate the capsize ratio for multiple boats and are looking for a way to save some time, then you can use a capsize ratio calculator to work it out for you.

You can also find the capsize ratio along with a load more data for almost every boat on Sailboat Data .

Conclusion: What Is Capsize Screening And How Is It Calculated?

Capsize ratio is just one tool that can be used to determine a boats suitability for sailing offshore. There are many factors that influence a boat’s capsize ratio, such as its design, loading, and weather conditions.

The capsize ratio of a boat is a useful tool, but isn’t an absolute, so it’s important to know your boat well before heading off on a longer passage away from the safety of land.

Hopefully this has help to explain capsize ration. If you’re looking for more tips and inspiration on all things sailing then make sure you follow us on social media, where we regularly share new articles and information on our lives aboard.

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Comparing capsize and comfort rates of boats

• Thread starter Richard Marble
• Start date Mar 16, 2004
• Forums for All Owners
• Ask All Sailors

Richard Marble

Here is a list of boats to compare. I have a 1981 Hunter 27. I know from sailing my boat that it feels very stable when it is rough out. I have been comparing the capsize factor and the comfort factor of my boat with other boats. Here is what I have found."Note" anything with a capsize factor over 2 I did not do a comfort factor on as they are more able to capsize so I didn’t figure it made much difference if you were comfortable. What surprised me is that a Hunter 27’s capsize and comfort rate is right up there with a Hunter 35.5 and is better than an Islander 32!!!If your boat is not here and you want to check it go to the related link.Hunter 27 1981Capsize factor of -1.94Comfort factor - 23.39Hunter 31 1985Capsize factor - 1.9Comfort factor - 24.55Hunter 28 1986Capsize 2.21 Not acceptableHunter 30 1983Capsize factor of -1.89Comfort factor - 25.21Hunter 33 1981Capsize factor of -1.86Comfort factor - 25.56Hunter 35.5 1995Capsize factor of -1.97Comfort factor - 24.57Irwin Citation 31 1979Capsize factor of -2.09 Not acceptablePearson 31 1978Capsize factor - 2.03 Not acceptableAllied Seawind 30 1965Capsize factor of - 1.62Comfort factor - 36.86Bristal 32 1966Capsize factor of - 1.74Comfort factor - 32Endeavour 32 year?Capsize factor of -1.76Comfort factor - 30.25Islander 32 year?Capsize factor of - 2.03 Not acceptableIslander Iona 32 year?Capsize factor of -1.9Comfort factor - 23.17Alberg 30 1968Capsize factor of -1.71Comfort factor - 30.97O’Day 32 1977Capsize factor of -1.91Comfort factor - 25.38Pearson 323 1983Capsize factor of -1.74Comfort factor - 30.88Kettenburg K32 1978Capsize factor of -1.86Comfort factor - 27.76  

Trevor - SailboatOwners.com

Another fun Sail Calculator Another fun Sail Calculator with an extensive database of boat models can be found at the Related link below. The program outputs a number of different categories in a bar chart format in a separate window. But remember, these are just numbers!Have fun,Trevor  

Be Careful With The Numbers Looking at these numbers are all well and good but they are derived from simple formulas and don't take into account many factors. And, additionally, how you setup your boat will change the numbers.For example:Capsize Ratio = Beam / (Displacement / 64)**0.333 Notice the only factors involved are Beam and Displacement. This means that, for the same displacement, a boat with a light-weight construction and a deep fin keel will have the same number as boat with heavy construction and a shoal-draft keel.To test what a few hundred pounds difference makes in displacement just run it through the formula and you will see that it makes a difference. If that little change in displacement makes that much difference just imagine what a difference taking into account the center of gravity and the lever arm would make. Think about that 8 or 9.9 hp outboard hanging on the stern rail, life raft and dingy on the coach roof, jerry cans of gas and water lashed to the life lines, etc.. Your numbers just changed big time.The formulas are "no brainers" but one needs to use a lot of judgment when using them.They make a good starting point for discussion, though, if you know what is behind them but don't treat them as gospel.  

Rough Numbers As John indicated, the MCR & CR don't consider all the numbers & variables, and should only be used for a very rough preliminary consideration of very similar boats.For instance (I'm paraphrasing Jeff_H from another forum):An extreme example: You could move a significant weight from a boat's deep keel to it's masthead, without affecting the formulaic outcome (very different boat realities, but same resulting ratios).Regards,Gord  

Richard A. Marble

Is there a better formula out there? I couldn't agree more. I wonder if there is a formula that takes the draft and keel weight into consideration. If there isn't why does'nt someone come up with one? It would be much better I would think.  

Isn't the CR really a righting ratio Richard, I am going to go off and confirm this info, but wasn't the capsize ratio developed by Ted Brewer to be an indication of a boats ability to recover from a capsize (the 180 position) and not specifically to be an indication of its initial stability? The factor favours less beamy boats which have less initial stability when upright, but when turned turtle the lack of beam means they can be uprighted more easily. And of course the greater and deeper the ballast the easier the righting process.I seem to recall Ted pointing out that today's modern beamy boats may not be able to right themseleves when inverted due to their wide beam.Kevin  

Laura Bertran

I've seen different numbers... ...right on this site. The capsize factor for a Hunter 31 is 2.13.  

The capsize screening formula is useful because wide light boats don't roll back up as quickly as narrow heavy boats. There are other numbers that can be calculated to give the range of positive stablity. It is odd that boat manufacturers almost never include this data. But for the few boats that I've compared if the CSF is low the boat is generally considered seaworthy. But even the range of positive stability may not be a better indication in that capsizing is a dynamic event and the RPS is a static measure. The CSF came about by looking at boats that survived the Fastnet?? disaster as opposed to those that didn't. It is an empirical observation rather than a theoretical calculation.  BTW I have a book that has a photo of a beamy fin keeler in the turtle position with the crew standing on the hull. Yes the keel is still attached!! Once that mast is underwater with sails it would take a lot to bring it back upright.  

newly anonymous

does not compute That capsize screening formula is almost universally criticised for being overly simplistic. It does not take into consideration the all-important ballast/displacement ratio, nor does it factor ballast/draft. If my boat displaces 20,000 pounds, it makes a tremendous difference whether 6,000 of those pounds are in ballast or 8,000 are. My H410, which displaces 20,000 pounds, has a bulb keel of 7,500. Surely this bulb keel gives it superior capsize stability than a fin keel would, but the formula doesn't take that into consideration. Neither does it factor whether I have the deep keel version or shoal draft. To simply factor beam verses displacement is ludicrous.  

Please give me an example of a cruising boat generally recognised as a seaworthy blue water cruiser that has a CSF greater than 2!!!!Check out allied seawind,Pacific seacraft,swans,cape dorys, etc etc I haven't done an extensive survey but every one that I have looked at had a CSF of 1.8 or less.  

Jeff M21319

IMHO, the calculation is so simplified... that it is useless. From an engineering viewpoint, so many relevant variables have been left out that any conclusions drawn using the formula presented are essentially false. While beam and displacement are important numbers, they certainly aren't the only ones that need to be considered and given a place in such a complex analysis. Kind of reminds me of the old 'skid charts' the police would use to determine the speed of a vehicle immediately prior to a colision. They would take the length of a skid mark, determine the type of road surface and then look it up on a little chart to get the estimated speed. No accounting for such things as vehicle weight, tread width, condition of tread, inflation pressure, etc. was done.  While I'm certainly not a naval architect, it would seem that determining a boats inherent ability to self-right after going inverted would require complex computer modeling, tank testing and perhaps other sophisticated methodology to get anywhere near a correct answer. Even then, one would have to look at variables such as type and size of sails aloft during the event, actions taken by the crew immediately prior to and after the event and a myriad of others. Sorry, but I just can't buy into a calculation so inherently flawed. P.S. Has anyone ever heard of or contemplated something along the lines of an auto-inflating PFD that would be mounted at the top of the mast and deploy after being submerged? I wonder what (if any) effect this would have, given a few hundred pounds of positive bouancy, on initiating a self-righting action? Perhaps I'm crazy (although it's never been proven in court!) but would something along the lines of a 4' diameter inflatable mooring ball tied to the top (bottom) of an inverted mast do much to get a 10 ton boat headed back onto her feet? What if it also had, via some mechanical means, the ability to 'blow' the main and jib halyards to remove the resistance of the sails to the righting movement? Just wondering.  

Just asked Bob Perry on cruising world's BB He didn't put much value on the CSF in and of itself. He said that bigger is better in that a longer boat is less likely to capsize. He also said that for cruisers that if you stay away from radical designs and have a moderate beam and displacement/length or 220 or better you'll probably be alright. But if you think about it a heavier boat D/L>220 and a moderate beam will probably give you a CSF of less than 2.0.Bob Perry please forgive me if I misquoted. My only attraction to the CSF is that it is a readily available number to compare boats. If you look at SA/Displ,Disp/wll, motion comfort ratio beam/length,PHRF etc you get an idea of what the boat is like. Of course all of these numbers are indications of how the boat probably will perform. Ideally you would have the time and money to hire an expert designer to evaluate the boat. But for some boats this would cost more than the boat!!!!!!  

So the verdict is According to what I’m reading, This capsize formula is pretty much worthless to really determine if your boat will capsize or if it will right itself. That said, generally speaking a boat with a higher number is probably less capable of staying upright than one that has a lower number. So when someone is looking at boats, I guess, use this formula but keep in mind that the lower the keel and the heavier the keel the better. Also you should keep in mind mast height and how much freeboard there is above the water line.Now why doesn’t someone come up with a better formula? While it may not be perfect I’m sure it could be better than this one.  

henkmeuzelaar

Uncomfortable truths about "comfort factors"..... What is the point of even discussing the value of such dimensionless empirical numbers when one is unlikely to find two sailors who completely agree on what "comfort" (or rather: "comfortable motion") at sea really is? Just try to start a rational discussion on this topic between avowed mono- and multi-hullers and you will soon see the futility of such an exercise.Perhaps we should all remember one other fact as well: there is currently no model (i.e. quantifiable level of understanding) that even begins to describe the dynamic behavior of a sailing vessel at sea. If that sounds like a bit of an exaggeration, just consider the fact that current models for boat speed at different points of sail and wind strengths are only valid for flat water! In other words, no one is even able to fully describe what the effects of seastate on something as straightforward as BOAT SPEED are...... IMHO, anyone who accepts the claim that some magical formula can predict the effect of seastate on something as complex as "comfortable motion in a seastate", while at the same time acknowledging that our current level of understanding is insufficient to predict something as comparatively simple as the effect of seastate on boat speed, would appear to have some issues to deal with that fall well outside the scope of this board.Have fun!Flying Dutchman  

You're Right Richard - Take With A Grain of Salt By jove I think you've got it! These formulas make a good starting point for discussion purposes.If nothing else, if your post got you thinking about what's going on that's good. You've started asking questions - that's good. Not taking everything hook-line-and sinker, that's good.I'm thinking about my own boat which is much the same as the Hunter 35.5 and has an aluminum toe rail. The Toe rail is bolted onto a flange on the hull and deck and sticks out about 2 or 3 inches. The beam is the width to the outside of the toe rail. So, do you plug in the manufacturers published number for the beam or use the beam measured to the outside of the hull? At 2" x 2 that's 1/3 of a foot, 0.333. At 3" x 2 that's 0.500 feet. Hey! That's significant!Then there are the other things that don't even fit "The Formula", like how one loads the boat, things one can do to rectify a bad situation (creative flotation devices were mentioned). So the point is there are a lot of variables that aren't in the formula. I guess if a point can be made that this MAY true with all the other formulas too so take the formulas with a grain of salt. The PHRF formula isn't exact either and it incudes many more variables but for speed on a race course, as a rule, it gets pretty darn close. There are exceptions, though, such as the handicap factor for a fixed-blade prop.Not only should one think about and question the forumulas, one should always be thinking when you're on the boat. Things happen and you have to be creative with ways to work your way out of a bad situation. Whether it's a squashed pinkiy up the inside passage (this happened to the Pardey's), getting a boat up-righted, or just getting between those two boats coming toward you in a narrow channel. We are really on our own out there, some times more than others, and you can't necessarily just call 911 to be taken care of.Bottom line - use the info with a grain of salt and think for yourself. And .... if your boat isn't reasonably water tight the best number in the world won't mean a thing.Now go out there and have fun.  

Henk Is your boat an FD=12?Dennis  

Nah, HL43. Tell us about your Windship, though! Flying Dutchman is just the nickname my crew gave me (probably because I am such a nice guy ;D). For the past decade, or so, I have been using this handle faithfully in order not to give anyone a chance to change it into Captain Bligh......The name of our Hunter Legend 43 (hull #1) is Rivendel II. Just type "Rivendel" under Search as far back as Phil's archives go these days and you will get a pretty good idea about what she's been up to.Have fun!Flying Dutchman  

Fred Ficarra

CSF I still believe in formulas that are used with caution. Take my chick screening formula as an example.weight X height in inches/ageX150. Usually women with a CSF of 2.2-1.8 are acceptable. If the number gets too high she is too fat or young. If the number gets too low she is too old ,short or skinny. If I throw in a couple of qualifying limits the results are better. Say older thatn 18 and younger than 35. But then you might get a perfect number and the girl be unacceptable for other reasons such as she doesn't like old farts!!!!Example a 62" woman weighing 120#s and 25 years old = 1.98 if she is 55 that number changes to =0.90 which is clearly an unacceptable number. Maybe I should factor in red hair and a large bank account???? But heck it's hard enough to get a woman to devulge her weight and age!!!!!!! Maybe a beer factor where .25 is added or subtracted for each beer consumed in the last hour????  

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Capsize Screening Formula (CSF)

Capsize Screening Formula for Boats and How to Measure It

Boating enthusiasts understand the thrill of being out on the water, but with adventure comes responsibility – especially when it comes to boat stability and safety. The concept of boat stability and the risk of capsize are crucial factors for anyone navigating water bodies. In this article, we’ll delve into a tool that holds the key to understanding and evaluating a boat’s stability: the capsize screening formula.

This formula is more than just a mathematical equation; it’s a powerful tool that provides essential insights into a boat’s potential for stability or vulnerability. As boaters, understanding the capsize screening formula and its components can greatly contribute to informed decision-making and safer voyages. Join us as we explore the depths of this formula, decode its components, and highlight its significance in ensuring enjoyable, secure boating experiences.

The Foundation of Boat Stability

When it comes to boating, stability forms the very foundation of a safe and enjoyable experience on the water. Stability refers to a boat’s capacity to maintain an upright position and resist tipping or capsizing, even in the face of challenging conditions. Understanding stability is essential because it directly impacts how a boat responds to waves, wind, and the movements of passengers onboard.

Stability isn’t just about comfort; it’s a critical factor in preventing capsizing – a situation where a boat overturns and potentially endangers passengers and crew. Ensuring a boat’s stability is paramount for maintaining control, avoiding accidents, and promoting confidence in boating endeavors. One powerful tool that aids in assessing a boat’s stability and potential capsize risk is the capsize screening formula. In the following sections, we’ll explore this formula’s components, how it works, and why it matters for safe boating practices.

Introducing the Capsize Screening Formula

The capsize screening formula is a mathematical equation designed to evaluate the potential risk of a boat capsizing under certain conditions. It’s a valuable tool that takes into account a range of factors related to a boat’s design and characteristics, all of which contribute to its overall stability on the water. By using this formula, boaters can gain insights into how susceptible a boat might be to capsizing, helping them make informed decisions about their waterborne activities.

The formula’s components include measurements of a boat’s beam (width), displacement (weight), and the vertical center of gravity. Additionally, the formula considers the boat’s form stability – how its shape influences stability – and the weight distribution of passengers, cargo, and other items on board. The capsize screening formula offers a standardized way to assess a boat’s stability potential, making it an invaluable asset for boating safety. In the upcoming sections, we’ll delve into the individual components of the formula and their significance.

Components of the Capsize Screening Formula

The capsize screening formula takes into account several key components that collectively influence a boat’s stability. Understanding these components is essential for comprehending how the formula assesses the risk of capsizing. Here’s a breakdown of the crucial elements:

• Beam (B) : The beam refers to the width of the boat, measured from side to side. A wider beam generally contributes to greater initial stability by providing a wider base. However, extreme width can also lead to decreased stability if not balanced with other factors.
• Displacement (D) : Displacement represents the weight of the boat, including its hull, equipment, passengers, and cargo. A heavier boat tends to be more stable because it resists tipping over, but excessive weight can compromise stability if not properly managed.
• Metacentric Height (GM) : The metacentric height is a measurement of the boat’s stability relative to its center of gravity. It represents the vertical distance between the center of gravity (G) and the metacenter (M), which is the point where the buoyant force acts. A higher GM value contributes to greater stability, as the boat is more likely to return to an upright position after a disturbance.

The interaction of these components determines a boat’s overall stability. A wider beam, higher displacement, and sufficient metacentric height contribute positively to stability. However, a balance must be struck between these factors to ensure optimal stability without compromising other aspects of boat performance. The capsize screening formula evaluates these components to provide a quantitative measure of a boat’s vulnerability to capsizing.

How the Formula Works

The capsize screening formula is a straightforward mathematical equation that quantifies a boat’s susceptibility to capsizing based on its dimensions and characteristics. The formula is as follows:

Capsize Screening Formula: GM/B ≤ 2.0

Here’s how to interpret and apply the formula:

• Calculate Metacentric Height (GM) : Subtract the center of gravity (G) height from the metacenter (M) height. This results in the metacentric height (GM), which represents the boat’s stability. A higher GM indicates better stability.
• Determine Beam (B) : Measure the width of the boat, known as the beam (B), in feet.
• Calculate GM/B Ratio : Divide the calculated metacentric height (GM) by the beam (B) of the boat.
• Compare to 2.0 : The resulting GM/B ratio is then compared to the value of 2.0. If GM/B is equal to or less than 2.0, the boat is considered stable within the parameters of the formula. If the ratio exceeds 2.0, the boat may have reduced stability and a higher risk of capsizing.

Interpreting the Result:

• GM/B ≤ 2.0: The boat is considered to have adequate stability based on the capsize screening formula.
• GM/B > 2.0: The boat may have reduced stability, and caution should be exercised, especially in adverse conditions.

It’s important to note that while the capsize screening formula provides a useful guideline, other factors such as hull design, weight distribution, and handling characteristics also influence a boat’s stability. Therefore, while the formula offers valuable insights, it’s not the sole determinant of a boat’s overall stability.

Capsize Screening Numbers

The capsize screening formula yields a numerical value known as the GM/B ratio, which serves as an indicator of a boat’s stability. Understanding the range of capsize screening numbers is essential for assessing a boat’s vulnerability to capsizing:

• GM/B ≤ 2.0 : A boat with a GM/B ratio equal to or less than 2.0 is considered stable based on the capsize screening formula. This indicates that the boat’s metacentric height (GM) is adequately balanced in relation to its beam (B), contributing to its stability.
• GM/B > 2.0 : If the GM/B ratio exceeds 2.0, the boat may have reduced stability, potentially leading to a higher risk of capsizing. A GM/B value above 2.0 suggests that the metacentric height (GM) is not as well-proportioned to the boat’s beam (B), which can negatively impact stability.

The significance of lower numbers indicating higher stability lies in the relationship between the metacentric height (GM) and the beam (B) of the boat. A smaller GM/B ratio suggests that the metacenter is located relatively higher above the center of gravity, promoting better stability by resisting tipping forces.

Boat designers and naval architects aim to achieve a balanced GM/B ratio that falls within the acceptable range for the boat’s intended use. However, it’s important to remember that while the capsize screening formula provides valuable insights, other factors such as hull shape, weight distribution, and handling characteristics also contribute to a boat’s overall stability.

While the capsize screening formula provides a valuable tool for assessing stability, there are additional factors beyond the formula that can significantly influence a boat’s stability. These factors should be considered to ensure safe boating experiences:

• Weight Distribution : The distribution of weight within a boat plays a crucial role in its stability. Uneven weight distribution, especially in smaller boats, can lead to imbalances that affect stability. Properly distributing passengers, gear, and equipment according to manufacturer recommendations is essential.
• Loading : Overloading a boat with excessive weight can lower its stability and increase the risk of capsizing. Boats have maximum weight capacities specified by the manufacturer. Exceeding these limits can compromise stability and safety.
• Modifications : Alterations to a boat’s design, structure, or equipment can impact stability. Modifications should be made with careful consideration of their potential effects on weight distribution and overall balance. Unauthorized modifications can compromise the boat’s stability and structural integrity.
• Freeboard and Buoyancy : The freeboard—the distance between the waterline and the upper deck—plays a role in a boat’s ability to resist capsizing. Boats with lower freeboard may be more susceptible to swamping, reducing stability. The buoyancy of the hull design also influences stability and the boat’s ability to handle waves.
• Manufacturer Recommendations : Manufacturers provide guidelines for proper loading, weight distribution, and maximum capacities. Following these recommendations is crucial for maintaining the boat’s intended stability and safety.
• Weather and Water Conditions : External factors like wind, waves, and current can impact a boat’s stability. Larger waves and rough waters increase the likelihood of capsizing, particularly if the boat’s stability is already compromised.
• Skill and Experience : The operator’s skill and experience in handling the boat also play a role in maintaining stability. Proper boating techniques, such as adjusting speed in adverse conditions, can help mitigate stability risks.

Ultimately, a combination of factors contributes to a boat’s stability, and understanding how they interact is essential for safe boating. While the capsize screening formula provides a starting point, boaters should also be attentive to weight distribution, loading, modifications, and other relevant considerations to ensure optimal stability and minimize the risk of capsizing.

Significance of the Capsize Screening Formula for Boating Safety

The capsize screening formula holds immense significance in ensuring boating safety by providing boaters with a valuable tool to assess and understand a boat’s stability characteristics. Here’s why the formula matters for safe boating:

• Informed Boat Selection : When choosing a boat, understanding its stability is crucial. By calculating and comparing capsize screening numbers, boaters can make informed decisions that align with their intended use. Boats with lower capsize screening numbers are generally more stable, making them better suited for a variety of conditions.
• Matching Conditions : Different boating conditions require different levels of stability. Using the capsize screening formula allows boaters to match the boat’s stability with the conditions they plan to navigate, ensuring a safer and more comfortable experience.
• Awareness of Limits : Knowing a boat’s capsize screening number raises awareness of its stability limits. Boaters can avoid overloading the boat, staying within recommended weight capacities, and maintaining proper weight distribution to prevent stability issues.
• Safe Navigation : Understanding a boat’s stability characteristics enables boaters to navigate confidently in varying conditions. It helps them anticipate how the boat will respond to waves, wind, and maneuvers, reducing the risk of sudden instability and capsizing.
• Preventing Capsizing : The formula’s application aids in preventing capsizing incidents by identifying potential risks in advance. Boaters can take appropriate measures to mitigate stability concerns, such as adjusting loading, changing course, or slowing down.
• Education and Awareness : Learning about the capsize screening formula encourages boaters to deepen their understanding of boat stability principles. This increased awareness fosters responsible boating practices and encourages adherence to safe loading and operating procedures.
• Minimizing Accidents : By incorporating stability considerations into their boating plans, boaters can help minimize accidents, improve onboard safety, and protect both themselves and their passengers.

Incorporating the capsize screening formula into boating practices enhances safety and responsible seamanship. It empowers boaters to make well-informed decisions about boat selection, loading, and navigation, contributing to safer and more enjoyable experiences on the water.

Limitations of the Capsize Screening Formula

While the capsize screening formula serves as a valuable tool for assessing boat stability, it’s important to recognize its limitations. Boaters should be aware of these limitations and complement the formula’s insights with practical experience and prudent boating practices. Here are some key limitations to consider:

• Simplified Model : The capsize screening formula is a simplified mathematical model that doesn’t account for all the complex factors that influence a boat’s stability. Real-world conditions, such as wind, waves, and currents, can interact in ways that the formula doesn’t fully capture.
• Static Analysis : The formula provides a static analysis of stability based on a boat’s specifications at rest. It doesn’t consider dynamic factors like how the boat’s stability changes when underway, during turns, or when encountering waves.
• Weight Distribution : The formula assumes an even weight distribution across the boat’s length. In reality, uneven weight distribution, such as passengers moving around, can significantly impact stability.
• Experience Matters : While the formula is a helpful starting point, experienced boaters understand that stability is influenced by a combination of factors. Practical knowledge gained through time on the water is essential for reading conditions, making real-time adjustments, and responding to changing situations.
• Prudent Practices : Even if a boat’s capsize screening number indicates acceptable stability, boaters should still exercise caution and adhere to prudent practices. Avoid overloading the boat, maintain proper weight distribution, and adjust speed and course in response to changing conditions.
• Boater Skill : The formula doesn’t account for the skills and experience of the operator. A skilled boater who understands how to handle a boat in different conditions can enhance stability through proper maneuvering.
• Custom Boats : Custom modifications to a boat can alter its stability characteristics beyond what the formula predicts. Any modifications should be carefully considered, and their impact on stability should be understood.

While the capsize screening formula provides a valuable framework for assessing stability, it’s not a substitute for sound judgment, experience, and responsible boating practices. Boaters should use the formula as a starting point for understanding stability but also rely on their own expertise to make informed decisions on the water.

Resources and Calculators

For boaters interested in assessing their boat’s stability using the capsize screening formula, there are several online resources and calculators available that provide convenient tools for this purpose. These resources can help you quickly determine your boat’s capsize screening number and better understand its stability characteristics. Here are a few websites and tools to consider:

• Boat Stability Calculator : Various boating organizations and websites offer boat stability calculators that allow you to input your boat’s specifications, such as beam, displacement, and metacentric height. These calculators will then provide you with the capsize screening number and help you interpret its implications.
• Manufacturer Websites : Some boat manufacturers provide calculators or guidelines on their websites to help boaters assess their boat’s stability. These resources are often tailored to the specific models they offer.
• Boating Forums : Online boating communities and forums can be excellent sources of information. Fellow boaters may share their experiences, insights, and even tools they have used to calculate capsize screening numbers.
• Boating Safety Organizations : Organizations dedicated to boating safety often provide educational resources and tools related to boat stability. These resources can offer valuable insights into how to use the capsize screening formula effectively.
• Boat Design Software : Certain boat design software applications or programs include stability calculation features. These tools are particularly useful for boat designers, but they can also be used by boaters to assess the stability of existing boats.

When using online calculators and resources, be sure to input accurate and up-to-date information about your boat’s specifications. Remember that the capsize screening formula is a helpful starting point, but it’s not a substitute for careful consideration, boating experience, and responsible operation. Using these resources in conjunction with your own boating knowledge will contribute to a safer and more enjoyable boating experience.

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Top 5 FAQs and answers related to capsize screening formula

What is the capsize screening formula .

The capsize screening formula is a mathematical equation used to assess a boat’s vulnerability to capsizing. It takes into account factors such as the boat’s beam (width), displacement (weight), and metacentric height (GM) to determine its stability characteristics.

How do I calculate the capsize screening number? 

The formula is: Capsize Screening Number = Beam / (Displacement / 64)^(1/3). You can find the boat’s beam and displacement in its specifications. Plug these values into the formula to calculate the capsize screening number, which indicates the boat’s stability.

What do different capsize screening numbers mean? 

Lower capsize screening numbers indicate higher stability. A lower number suggests that a boat is less likely to capsize. Higher numbers imply reduced stability, and boats with higher numbers might be less suitable for certain conditions.

Can I solely rely on the capsize screening number to assess a boat’s stability? 

While the capsize screening formula is a useful tool, it doesn’t account for all real-world scenarios. Factors like weight distribution, loading, modifications, and sea conditions can influence a boat’s stability. It’s important to consider these factors along with the capsize screening number.

Where can I find resources to calculate the capsize screening number?

There are various online resources and calculators available on boating websites, manufacturer websites, boating forums, and even boat design software. These tools allow you to input your boat’s specifications to calculate the capsize screening number. However, remember that these tools provide a starting point, and prudent boating practices and experience are essential for safe navigation.

In conclusion, the capsize screening formula serves as a valuable tool in assessing a boat’s stability, offering insights into its vulnerability to capsizing. By considering factors such as beam, displacement, and metacentric height, boaters can gain a clearer understanding of their vessel’s stability characteristics. This knowledge aids in making informed decisions about boat selection and operation, ultimately contributing to a safer and more enjoyable boating experience.

While the formula provides essential insights, it’s important to remember its limitations. Real-world conditions, weight distribution, and other variables can influence stability beyond the formula’s scope. As boaters, relying on experience, prudent practices, and manufacturer guidelines is equally crucial.

By utilizing online calculators and resources, boaters can easily apply the capsize screening formula to their vessels and gain valuable insights into their stability profiles. With this knowledge in hand, boaters can navigate the waters with confidence, prioritizing safety and enhancing their enjoyment on every journey.

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Capsize – how it happens

Posted by John Vigor | Sailing Tips

Planning for an unplanned inversion

Capsize: how it happens, and what you can do to survive it.

When Isabelle Autissier’s 60-foot racer capsized in the Southern Ocean, it sent a chill of fear through the sailing community. Sailors don’t like to think of capsize. But here was a big, well-found boat, a Finot-designed Open 60 Class flier, wallowing upside down in huge frigid swells, with her long thin keel jutting toward heaven. It was a bizarre and frightening sight.

Autissier was lucky. She was taking part in the Around Alone race, so her million-dollar boat was equipped with emergency satellite transmitters, position recorders, and lots of other equipment that no normal cruiser is likely to be able to afford or fit on board. She was eventually rescued in a wonderful feat of seamanship by Giovanni Soldini, a fellow competitor.

So what went wrong? And could it happen to you? It depends where you sail, but if you sail out of sight of land, whether at sea or on a lake, the answer is yes, it could. And you should always be prepared for it to happen. The good news is that most yachts of classic proportions will survive a capsize. Unlike Autissier’s extreme design, they will right themselves, although some might take longer than others.

You can form a crude idea of what went wrong with Autissier’s boat by imagining a long plank floating in the water. It doesn’t care which side is up. It’s happy floating either way up. That’s Autissier’s boat. Now imagine a plank with a heavy weight attached along one side, so the plank floats on edge. If you turn it upside down, the ballast quickly pulls it back again. That’s your normal yacht design. Autissier’s racer was shaped too much like a wide plank – too beamy and too light to recover from an inverted position, despite the long heavy keel. It’s one of the paradoxes of naval architecture that an excessively beamy boat, while hard to capsize in the first place, is unseaworthy if she is inverted.

Furthermore, a light, shallow, beamy boat capsizes more easily than a narrow, deep, heavy boat because she offers the seas more leverage to do their work, and because she is quicker to respond to the upward surge of a large swell.

Planing hulls

Designers create racing boats like Autissier’s because that shape gives them the ability to plane at high speeds. In other words, they deliberately sacrifice seaworthiness on the altar of speed, and the boats rely on the skill of their crews to keep them upright. Unfortunately, singlehanders have to sleep now and then, so they can’t be on watch all the time.

While it’s true that a good big boat is less likely to capsize than a good small boat, there is no guarantee that even the largest yachts are immune from capsize. It’s not the wind that’s the problem. It’s the waves.

Tests carried out at Southampton University in England have shown that almost any boat can be turned turtle by a breaking wave with a height equal to 55 percent of the boat’s overall length. Even if you don’t like to think about it, you know in your heart that it’s a reasonable finding. It means your 35-footer could be capsized through 180 degrees by a 20-foot wave. Even a 12-foot breaking wave would roll her 130 degrees from upright – from which position she may turn turtle anyhow.

And if you imagine you’re never going to encounter a 20-foot wave, think again. Waves of that size can be generated in open water by a 40-knot wind blowing for 40 hours. And a 12-foot wave is the result of a 24-knot wind blowing for 24 hours. Plenty of those around.

Large waves are formed in other ways, too. A current flowing against the wind will create seas that are much larger and steeper than normal. And the old stories about every seventh wave being bigger than the rest have a basis of truth, although it’s not necessarily the seventh wave. It could be the fifth or the ninth. The point is that wave trains occasionally fall in step with each other at random intervals, literally riding on one another’s backs, to form an exceptionally high wave. We call that a freak wave, but it’s actually more normal than we care to admit.

Bigger waves

Scientists calculate that one wave in every 23 is more than twice as high as the average. One in 1,175 is three times bigger. And one in 300,000 is four times the average height. They may be far apart, but they’re out there, and many big ships have been lost to them.

John Lacey, a British naval architect, put forward an interesting proposition after the 1979 Fastnet Race, in which 63 yachts experienced at least one knock-down that went farther than 90 degrees and remained upside down for significant periods.

He explained that the old International Offshore Rule for racers had radically changed the shape of yacht hulls by greatly increasing the proportion of beam to length, which gave them more power to carry sail without the need for additional ballast. It also gave them more room below, of course.

But the flatiron shape of the hull made it very stable when it was inverted. To bring the boat upright again would require about half the energy needed to capsize the yacht in the first place, Lacey calculated.

“Since the initial capsize may have been caused by a once-in-a-lifetime freak wave, one could be waiting a long time for a wave big enough to overcome this inverted stability,” he commented. Autissier’s experience bore out that prophetic statement. Her boat was still upside down when she abandoned it.

Lacey did some more sums and figured that a narrower cruising hull with a lower center of gravity than a typical IOR boat would require only one-tenth of the capsize energy to recover from a 180-degree capsize.

“It therefore seems, in my opinion, that we should tackle the problem from the other end, and design yachts for minimum stability when upside down,” he concluded.

Deep-vee cabin

His recommendation is not likely to be taken too seriously, but he certainly does have a point. You could make an inverted yacht unstable with narrow beam, a very deep keel with a lot of weight at the very end of it for righting leverage, and a deep-vee cabintop, or at least one that was narrow on top and broad at deck level. For the same reason, flush-decked yachts should be avoided, because they’re likely to be much more stable upside down.

But as in everything to do with sailboats, there are compromises to be made. Deep narrow hulls might recover quickly from inversion, but as sailors discovered a century ago when they were all the rage, they’re lacking in buoyancy. They’re also wet, and they have very little accommodation.

Two basic design features probably govern the probability of capsize more than any others. The first is inertia and the second is the shape of the keel.

Inertia is not generally well understood, but it’s the first line of defense against a wave impact. In simple terms, inertia is resistance to change. The inertia of a moving boat works to keep her moving on course, even though other forces are trying to halt or divert her. The inertia of a boat at rest resists any sudden attempt to start her moving.

Obviously, because inertia varies with mass, a heavy boat has more inertia than a light boat, so a wave hitting her from the side is going to get a slower response. Light-displacement boats are more likely than heavy boats to be picked up and hurled over by a plunging breaker.

Narrow beam is a help, too, because the force of a breaking wave is concentrated nearer the centerline of the yacht, where it has less overturning leverage.

Spreading weight

The way weight is distributed on a boat also affects its inertia. A wide boat with a light mast and a shallow keel will respond very quickly to every wave with a lively, jerky motion. A boat with a heavier mast and a deeper keel has its weight spread out over a greater span, and it’s more difficult to change its speed or direction, so the force of a breaking wave may be dissipated before it has a chance to overturn the boat. Inertia, incidentally, is what keeps a tightrope walker aloft. It’s contained in that long stick. If you push down on one side of it suddenly to regain your balance, it almost bounces back at you. It will subsequently move slowly away, but you can recover it with a long gentle pull as you lean the other way.

A long, old-fashioned keel resists sudden rolling simply because it’s difficult to move anything that big sideways through the water. A fin keel, with its meager surface area, is much more easily moved when it’s stalled; thus, the boat to which it’s attached is more easily overturned. But a fin keel that’s moving through the water acquires much more stability, which is why fin keelers should be kept moving in heavy weather.

Capsize screening formula

The maximum beam divided by the cube root of the displacement in cubic feet, or Maximum beam (feet) = less than 2 3÷Displ/64 The displacement in cubic feet can be found by dividing the displacement in pounds by 64. The boat is suitable for offshore passages if the result of the calculation is 2.0 or less, but the lower the better.

Although there are design factors that improve seaworthiness (usually at the expense of speed and accommodation), and although there are tactics you can use in a storm to minimize the chances of overturning, no boat is totally capsize-proof. That is not to say that every boat is going to capsize, of course, even the ones most likely to. After all, hundreds of yachts cross oceans every year without mishap. But prudent sailors keep the possibility in mind and do what they can to forestall any problems and to lessen any damage resulting from an inversion.

Large forces

If you have never given any thought to inversion, the results of a capsize can be devastating, not only on deck but down below as well. Not many people realize what large forces are involved in a capsize, especially the head-over-heels capsize called a pitchpole. It’s not just a gentle rolling motion. The contents of lockers and drawers can be flung long distances in the saloon, and you could easily find yourself standing in a state of disorientation on the overhead in a seething mess of battery acid, salt water, clothing, ketchup, mayonnaise, diesel fuel, paint thinner, knives, forks, and shards of broken glass. There will be no fresh air entering the cabin to dissipate the fumes. And it will be dark because your ports will be under water.

So, first things first: presuming you haven’t been injured by flying objects, can you lay hands on flashlights? Were they stored safely in a special place that you can reach without having to shift a wodge of soaked bunk mattresses? Is there one for every member of the crew? Are the batteries fresh? You may not stay upside down for long. But if you’re unlucky, like Isabelle Autissier, you will find you need a flashlight more than anything else on earth.

There are some other things you should think about before you ever set sail. And there are some precautions you can take.

Avoiding capsize

• Avoid heavy weather. “The most dangerous thing on a boat is an inflexible schedule.” Thanks to Tony Ouwehand for this observation.
• Avoid taking large waves abeam, particularly breaking waves.

Heave to. Run (down wave) using a drogue to keep speed down to 3 to 5 knots. Use a sea anchor from the bow or a series drogue from the stern. (Practice rigging and deploying these in moderate conditions.)

• Is your rig as strong as possible? Will it withstand the tremendous forces of a capsize?
• Do you have a plan to free a toppled mast from alongside, where it can batter holes in your hull? Have you ever thought how difficult it would be to cut the rigging, even with a decent pair of bolt cutters, on a slippery deck that’s suddenly rolling viciously?
• Do you have material on board for a jury rig? Have you thought about how you would use it?
• Will your radio transmitter’s antenna come down with the rig? Do you have a spare?
• Will your EPIRB start working automatically because it’s been under water – whether you want it to or not?

The cockpit

• Are your cockpit lockers waterproof? Can you imagine how quickly you’d sink if one of them was open at the time of capsize?
• Do your companionway hatchboards lock in position? Have you ever thought how much water would get below if one or more fell out as you turned over?
• What have you done about waterproofing the cowl vents for the engine? Those are huge holes in what would become the bottom of the boat. (The same goes for Dorade boxes, incidentally. Each one is a potential three- or four-inch hole in the bottom. Fit them with deck plates for sea work, on deck and down below.)
• If you’re in the cockpit when the boat capsizes, will you be attached by a harness? Will you be able to free yourself if you’re trapped under water and the boat stays inverted for some time?

The anchor locker

• If the anchors and chain are not fastened down securely they could bash their way through the locker lid and cause all kinds of havoc.
• Is your self-draining deck anchor locker waterproof? Many aren’t completely sealed at the top, where wires for pulpit-mounted running lights come though, and would let in water.

The engine room

• Is your engine mounted securely enough to withstand a capsize? I know of one boat in which the engine was hurled from its mounts during a pitchpole, causing great destruction.
• What if the engine’s running during a capsize? Could you switch it off quickly, with everything upside down? Would the oil run out? Would the fuel drip out of the tanks? Are your breathers inside or outside?
• Are the batteries fastened down firmly enough? Can you imagine what damage they could do if they got loose? And will they drip acid if they’re upside down? (Newer batteries – gel cells and AGMs will not spill acid when inverted. -Ed.)
• Can you turn the stove off? If there’s a smell of gas, can you deal with it? Have you made sure the galley cupboards can’t fly open during a capsize and turn the saloon into a sea of broken glass and chip dip?
• Can you lay hands on a fire extinguisher quickly? It could save your life.
• Have you figured out a way to keep all those loose tops in place in the saloon – the boards that cover access to storage under bunks, the bilge boards, and so on? Some boats have inside ballast, and many have heavy objects, such as storm anchors, stowed in the bilges. Make sure they stay there, because if they get loose they can come crashing through the overhead (your new “floor”) and sink the boat very quickly.
• Make sure your bunk mattresses will stay in place, too, otherwise they will greatly hamper your attempts to get around.
• Have you figured out a way to pump bilge water out of an inverted boat? Think about it. It’s not easy.
• Most books could escape from their racks during a capsize and become potentially harmful flying objects. Have you solved that problem?

Important documents

• The ship’s papers and your own personal documents should be in a watertight container in a secure locker, one that is not too high up in the boat because that’s where the water will be when you capsize.

There are many other systems and pieces of gear on a boat that could be affected by a capsize. When you use them, think inverted. Imagine what would happen if they got loose. Invent ways to keep things in their places during an unplanned inversion. Don’t ever imagine it’s wasted work. It’s one of the unspoken rules of the sea that if you’re prepared, the worst is not likely to happen. If you’re not, you’re bound to attract trouble.

More on the subject

Tami Ashcraft wrote a compelling story of the realities of inversion and its aftermath in her book, Red Sky in Mourning: The True Story of a Woman’s Courage and Survival at Sea , reviewed in our May 2000 issue. John Vigor goes into more depth about preparation for capsize in his book, The Seaworthy Offshore Sailboat .

Article from Good Old Boat magazine, November/December 2000.

About The Author

John Vigor is a retired journalist and the author of 12 books about small boats, among them Things I Wish I’d Known Before I Started Sailing, which won the prestigious John Southam Award, and Small Boat to Freedom. A former editorial writer for the San Diego Union-Tribune, he’s also the former editor of Sea magazine and a former copy editor of Good Old Boat. A national sailing dinghy champion in South Africa’s International Mirror Class, he now lives in Bellingham, Washington. Find him at johnvigor.com.

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Calculating Sailboat Design Ratios

Without having to wrestle with the mathematics.

Not only do the Sailboat Design Ratios tell us a great deal about a cruising boat's performance and handling characteristics, they also enable us to make objective comparisons between individual designs.

Here are the five main ones in common use by yacht designers and the formulae from which they are derived.

Five Key Sailboat Design Ratios:

The displacement/length ratio.

D/L Ratio = D/(0.01L) 3

Where D is the boat displacement in tons (1 ton = 2,240lb), and L is the waterline length in feet.

The Sail Area/Displacement Ratio

SA/D = SA/D 0.67

Where SA is sail area in square feet, and D is displacement in cubic feet.

The Ballast Ratio

BR = (B/D) x 100

Where B is ballast in lbs, and D is displacement in lbs.

The Capsize Screening Formula

CSF = 3 √(Bm/D)

Where Bm is the maximum beam in feet, and D is displacement in cubic feet.

The Comfort Ratio

CR = D/[0.65 x (0.7L 1 +0.3L 2 ) x Bm 1.33 ]

Where D is displacement in pounds, L 1 is waterline length in feet and L 2 is length overall in feet, and Bm is the maximum beam in feet.

Problem is, can you always trust the ratios published by the manufacturers? The answer, sadly, is "no".

So when you think you're comparing like-for-like, you may not be.

But let's be generous, it's not always an intentional deceit - there are two main parameters where ambitious data can lead to misleading Design Ratios. These are found in the manufacturers' published data for displacement and sail area .

In almost all yacht manufacturers' published data, displacement is quoted as the ‘light ship’ or unladen weight displacement.

This is unrealistic, as the laden weight of a fully equipped cruising boat is much higher.

As displacement is a key parameter in all of the Design Ratios, the laden weight should be taken account of when comparing one boat’s ratios with those of another.

Published SA/D ratios can similarly be misleading as some manufacturers, keen to maximize their vessels’ apparent performance, quote the actual sail areas which could be based on a deck-sweeping 150% genoa. On paper this would compare unjustly well against a competitor’s boat that has the ratio calculated on the basis of a working jib. 

Making an objective comparison between two such sets of SA/D ratios would be impossible.

An objective comparison can only be made if sail areas are calculated on the same basis using the J, I, P and E measurements as set out in the above sketch.

So now to the point...

What we have here is our  Interactive  S ailboat Design Ratio Calculator , which does all the calculations for you instantly and avoids all the pitfalls described above. The pic below is where you would enter the dimensional data on the downloaded Design Ratio Calculator :

The following pic shows the Design Ratios which are automatically calculated in the blink of an eye!

Download the Sailboat Design Ratio Calculator...

The  Interactive  Sailboat Design Ratio Calculator is  accompanied by a free eBooklet 'Understanding Sailboat Design Ratios' which will help you make sense of the numbers. 

Our 'Sailboat Design Ratio Calculator' takes all the hard work out of calculating the numbers and  will provide a valuable insight into a sailboat's performance and handling characteristics.

We make a small charge of $4.99 for this useful tool as a contribution towards the costs of keeping this website afloat. 

This  Sailboat Design Ratio Calculator and eBooklet  comes with a No-Quibble Guarantee!

Sailboat-Cruising.com's Promise to You:

"I'm so sure that you'll be absolutely delighted with your purchase that I'll refund in full the price you paid if you're dissatisfied in any way" , promises

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MODERN SAILBOAT DESIGN: Quantifying Stability

We have previously discussed both form stability and ballast stability as concepts, and these certainly are useful when thinking about sailboat design in the abstract. They are less useful, however, when you are trying to evaluate individual boats that you might be interested in actually buying. Certainly you can look at any given boat, ponder its shape, beam, draft, and ballast, and make an intuitive guess as to how stable it is, but what’s really wanted is a simple reductive factor–similar to the displacement/length ratio , sail-area/displacement ratio , or Brewer comfort ratio –that allows you to effectively compare one boat to another.

Unfortunately, it is impossible to thoroughly analyze the stability of any particular sailboat using commonly published specifications. Indeed, stability is so complex and is influenced by so many factors that even professional yacht designers find it hard to quantify. Until the advent of computers, the calculations involved were so overwhelming that certain aspects of stability were only estimated rather than precisely determined. Even today, with computers doing all the heavy number crunching, stability calculations remain the most tedious part of a naval architect’s job.

There are, however, some tools available that you can use to make a sophisticated appraisal of a boat’s stability characteristics. If you dig and scratch a bit–on the Internet, or by pestering a builder or designer–you should be able to unearth one or more of them.

Stability Curves and Ratios

The most common tool used to assess a boat’s form and ballast stability is a stability curve. This is a graphic representation of a boat’s self-righting ability as it is rotated from right side up to upside down. Stability curves are sometimes published or otherwise made available by designers and builders, but to interpret them correctly, you first need to understand the physics of a heeling sailboat.

When perfectly upright, a boat’s center of gravity (CG)–which is a function of its total weight distribution (i.e., its ballast stability)–and its center of buoyancy (CB)–which is a function of its hull shape (i.e., its form stability)–are vertically aligned on the boat’s centerline. CG presses downward on the boat’s hull while CB presses upward with equal force. The two are in perfect equilibrium, and the boat is motionless. If some force heels the boat, however, CB shifts outboard of CG and the equilibrium is disturbed. The horizontal distance created between CG and CB as the boat heels is called the righting arm (GZ). This is a lever arm, with CG pushing down on one end and CB pushing up on the other, and their combined force, known as the righting moment (RM), works to rotate the hull back to an upright position. The point around which the hull rotates is known as the metacenter (M) and is always directly above CB.

The longer the righting arm (i.e., the larger the value for GZ), the greater the righting moment and the harder the hull tries to swing upright again. Up to a point, as a hull heels more, its righting arm just gets longer. The righting moment, consequently, gets larger and larger. This is initial stability. A wider hull has greater initial stability simply because its greater beam allows CB to move farther away from CG as it heels. Shifting ballast to windward also moves CG farther away from CB, and this too lengthens the righting arm and increases initial stability. The angle of maximum stability (AMS) is the angle at which the righting arm for any given hull is as long as it can be. This is where a hull is trying its hardest to turn upright again and is most resistant to further heeling.

Once a hull is pushed past its AMS, its righting arm gets progressively shorter and its ability to resist further heeling decreases. Now we are moving into the realm of ultimate, or reserve, stability. Eventually, if the hull is pushed over far enough, the righting arm disappears and CG and CB are again vertically aligned. Now, however, the metacenter and CG are in the same place, and the hull is metastable, meanings it is in a state of anti-equilibrium. Its fate hangs in the balance, and the least disturbance will cause it to turn one way or the other. This point of no return is the angle of vanishing stability (AVS). If the hull fails to right itself at this point, it must capsize. Any greater angle of heel will cause CG and CB to separate again, except now the horizontal distance between them will be a capsizing arm, not a righting arm. Gravity and buoyancy will be working together to invert the hull.

Stability at work. The righting arm (GZ) gets longer as the center of gravity (CG) and the center of buoyancy (CB) get farther apart, and the boat works harder to right itself. Past the angle of vanishing stability, however, the righting arm is negative and CG and CB are working to capsize the boat

A stability curve is simply a plot of GZ–including both the positive righting arm and the negative capsizing arm–as it relates to angle of heel from 0 to 180 degrees. Alternatively, RM (that is, both the positive righting moment and the negative capsizing moment) can be the basis of the plot, as it derives directly from GZ. (To find RM in foot-pounds, simply multiply GZ in feet by the boat’s displacement in pounds.) In either case, an S-curve plot is typical, with one hump in positive territory and another hopefully smaller hump (assuming the boat in question is a monohull) in negative territory.

The AMS is the highest point on the positive side of the curve; the AVS is the point at which the curve moves from positive to negative territory. The area under the positive hump represents all the energy that must be expended by wind and waves to capsize the boat; the area under the negative hump is the energy (usually only waves come into play here) required to right the boat again. To put it another way: the larger the positive hump, the more likely a boat is to remain right side up; the smaller the negative hump, the less likely it is to remain upside down.

Righting arm (GZ) stability curve for a typical 35-foot cruising boat. The angle of maximum stability (AMS) in this case is 55 degrees with a maximum GZ of 2.6 feet; the angle of vanishing stability (AVS) is 120 degrees; the minimum GZ is -0.8 feet

The relationship between the sizes of the two humps is known as the stability ratio. If you have a stability curve to work from, there are some simple calculations developed by designer Dave Gerr that allow you to estimate the area under each portion of the curve. To calculate the positive energy area (PEA), simply multiply the AVS by the maximum righting arm and then by 0.63: PEA = AVS x max. GZ x 0.63. To calculate the negative energy area (NEA), first subtract the AVS from 180, then multiply the result by the maximum capsizing arm (i.e., the minimum GZ) and then by 0.66: NEA = (180 – AVS) x min. GZ x 0.66. To find the stability ratio divide the positive area by the negative area.

Working from the curve shown in the graph above for a typical 35-foot cruising boat, we get the following values to plug into our equations: AVS = 120 degrees; max. GZ = 2.6 feet; min. GZ = -0.8 feet. The boat’s PEA therefore is 196.56 degree-feet: 120 x 2.6 x 0.63 = 196.56. Its NE is 31.68 degree-feet: (180 – 120) x -0.8 x 0.66 = 31.68. Its stability ratio is thus 6.2: 196.56 ÷ 31.68 = 6.2. As a general rule, a stability ratio of at least 3 is considered adequate for coastal cruising boats; 4 or greater is considered adequate for a bluewater boat. The boat in our example has a very healthy ratio, though some boats exhibit ratios as high as 10 or greater.

You can run these same equations regardless of whether you are working from a curve keyed to the righting arm or the righting moment. The curve in our example is a GZ curve, but if it were an RM curve, we only have to substitute the values for maximum and minimum RM for maximum and minimum GZ. Otherwise the equations run exactly the same way. The results for positive and negative area, assuming RM is expressed in foot-pounds, will be in degree-foot-pounds rather than degree-feet, but the final ratio will be unaffected.

GZ and RM curves are not, however, interchangeable in all respects. When evaluating just one boat it makes little difference which you use, but when comparing different boats you should always use an RM curve. Because righting moment is a function of both a boat’s displacement and the length of its righting arm, RM is the appropriate standard for comparing boats of different displacements. It is possible for different boats to have the same righting arm at any angle of heel, but they are unlikely to have the same stability characteristics. It always takes more energy to capsize a larger, heavier boat, which is why bigger boats are inherently more stable than smaller ones.

Righting moment (RM) stability curves for a 19,200-pound boat and a 28,900-pound boat with identical GZ values. Because heavier boats are inherently more stable, RM is the standard to use when comparing different boats (Data courtesy of Dave Gerr)

Another thing to bear in mind when comparing boats is that not all stability curves are created equal. There are various methods for constructing the curves, each based on different assumptions. The two most commonly used methodologies are based on standards promulgated by the International Measurement System (IMS), a once popular rating rule used in international yacht racing, and by the International Organization for Standardization (ISO). Many yacht designers have developed their own methods. When comparing different boats, you must therefore be sure their curves were constructed according to the same method.

Perfect Curves and Vanishing Angles

To get a better idea of how form and ballast relate to each another, it is useful to compare curves for hypothetical ideal vessels that depend exclusively on one type of stability or the other. A vessel with perfect form stability, for example, would be shaped very much like a wide flat board, and its stability curve would be perfectly symmetrical. Its AVS would be 90 degrees, and it would be just as stable upside down as right side up. A vessel with perfect ballast stability, on the other hand, would be much like a ballasted buoy–that is, a round, nearly weightless flotation ball with a long stick on one side to which a heavy weight is attached, like a pick-up buoy for a mooring or a man-overboard pole. The curve for this vessel would have no AVS at all; there would be just one perfectly symmetric hump with an angle of maximum stability of 90 degrees. The vessel will not become metastable until it reaches the ultimate heeling angle of 180 degrees, and no matter which way it turns at this point, it must right itself.

Ideal righting arm (GZ) stability curves: vessel A, a flat board, is as stable upside down as it is right side up; vessel B, a ballasted buoy, must right itself if turned upside down (Data courtesy of Danny Greene)

Beyond the fact that one curve has no AVS at all and the other has a very poor one, the most obvious difference between the two is that the board (vessel A) reaches its point of no return at precisely the point that the buoy (vessel B) achieves maximum stability. A subtler but critical difference is seen in the shape of the two curves between 0 and 30 degrees of heel, which is the range within which sailboats routinely operate. Vessel A achieves its maximum stability precisely at 30 degrees, and the climb of its curve to that point is extremely steep, indicating high initial stability. Vessel B, on the other hand, exhibits poor initial stability, as the trajectory of its curve to 30 degrees is gentle. Indeed, heeling A to just 30 degrees requires as much energy as is needed to knock B down flat to 90 degrees.

Righting arm (GZ) stability curves for a typical catamaran and a typical narrow, deep-draft, heavily ballasted monohull. Note similarities to the ideal curves in the last figure

To translate this into real-world terms, we need only compare the curves for two real-life vessels at opposite extremes of the stability spectrum. The curve for a typical catamaran, for example, looks similar to that of our board since its two humps are symmetrical. If anything, however, it is even more exaggerated. The initial portion of the curve is extremely steep, and maximum stability is achieved at just 10 degrees of heel. The AVS is actually less than 90 degrees, meaning that the cat, due to the weight of its superstructure and rig, will reach its point of no return even before it is knocked down to a horizontal position. The curve for a narrow, deep-draft, heavily ballasted monohull, by comparison, is similar to that of the ballasted buoy. The only significant difference is that the monohull has an AVS, though it is quite high (about 150 degrees), and its range of instability (that is, the angles at which it is trying to capsize rather than right itself) is very small, especially when compared to that of the catamaran.

The catamaran, due to its light displacement and great initial stability, will likely perform well in moderate conditions and will heel very little, but it has essentially no reserve stability to rely on when conditions get extreme. The monohull because of its heavy displacement (much of it ballast) and great reserve stability, will perform less well in moderate conditions but will be nearly impossible to overturn in severe weather.

What Is An Adequate AVS?

In the real world you will rarely come across stability curves for catamarans. If you do find one, you should probably be most interested in the AMS and the steepness of the curve leading up to it. Monohull sailors, on the other hand, should be most interested in the AVS, and as a general rule the bigger this is the better.

Coastal cruisers sailing in protected waters should theoretically be perfectly safe in a boat with an AVS of just 90 degrees. Assuming you never encounter huge waves, the worst that could happen is you will be knocked flat by the wind, and so as long as you can recover from a 90-degree knockdown, you should be fine. It’s nice to have a safety margin, however, so most experts advise that average-size coastal cruising boats should have an AVS of at least 110 degrees. Some believe the minimum should 115 degrees.

For offshore sailing you want a larger margin of safety. Recovering from a knockdown in high winds is one thing, but in a survival storm, with both high winds and large breaking waves, there will be large amounts of extra energy available to help roll your boat past horizontal. There is near-universal consensus that bluewater boats less than 75 feet long should have an AVS of at least 120 degrees. Because larger boats are inherently more stable, the standard for boats longer than 75 feet is 110 degrees.

The reason 120 degrees is considered the minimum AVS standard for most bluewater boats is quite simple. Naval architects figure that any sea state rough enough to roll a boat past 120 degrees and totally invert it will also be rough enough to right it again in no more than 2 minutes. This, it is assumed, is the longest time most people can hold their breaths while waiting for their boats to right themselves. If you don’t ever want to hold your breath that long, you want to sail offshore in a boat with a higher AVS.

Estimated times of inversion for different AVS values (Data courtesy of Dave Gerr)

As this graph illustrates, an AVS of 150 degrees is pretty much the Holy Grail. A boat with this much reserve stability can expect to meet a wave large enough to turn it right side up again almost the instant it’s turned over.

Other Factors To Consider

Stability curves may look dynamic and sophisticated, but in fact they are based on relatively simple formulas that can’t account for everything that might make a particular boat more or less stable in the real world. For one thing, as with regular performance ratios, the displacement values used in calculating stability curves are normally light-ship figures and do not include the weight that is inevitably added when a boat is equipped and loaded for cruising. Even worse, much of this extra weight–in the form of roller-furling units, mast-mounted radomes, and other heavy gear–will be well above the waterline and thus will erode a boat’s inherent stability. The effect can be quite large. For example, installing an in-mast furling system may reduce your boat’s AVS by as much as 20 degrees. In most cases, you should assume that a loaded cruising boat will have an AVS at least 10 degrees lower than that indicated on a stability curve calculated with a light-ship displacement number.

Another important factor to consider is downflooding. Stability curves normally assume that a boat will take on no water when knocked down past 90 degrees, but this is unlikely in the real world. The companionway hatch will probably be at least partway open, and if the knockdown is unexpected, other hatches may be open as well. Water entering a boat that is heeled to an extreme angle will further destabilize the boat by shifting weight to its low side. If the water sloshes about, as is likely, this free-surface effect will make it even harder for the boat to come upright again.

This may seem irrelevant if you are a coastal cruiser, but if you are a bluewater cruiser you should be aware of the location of your companionway. A centerline companionway will rarely start downflooding until a boat is heeled to 110 degrees or more. An offset companionway, however, if it is on the low side of the boat as it heels, may yield downflood angles of 100 degrees or lower. A super AVS of 150 degrees won’t do much good if your boat starts flooding well before that. To my knowledge, no commonly published stability curve accounts for this factor.

Another issue is the cockpit. An open-transom cockpit, or a relatively small one with large effective drains, will drain quickly if flooded in a knockdown. A large cockpit that drains poorly, however, may retain water for several minutes, and this, too, can destabilize a boat that is struggling to right itself.

This boat has features that can both degrade and improve its stability. The severely offset companionway makes downflooding a big risk during a port tack knockdown or capsize, but the high rounded cabintop and small cockpit footwell will help the boat to right itself

Fortunately, not all unaccounted for stability factors are negative. IMS-based stability curves, for example, assume that all boats have flush decks and ignore the potentially positive effect of a cabin house. This is important, as a raised house, particularly one with a rounded top, provides a lot of extra buoyancy as it is submerged and can significantly increase a boat’s stability at severe heel angles. Lifeboats and other self-righting vessels have high round cabintops for precisely this reason.

ISO-based stability curves do account for a raised cabin house, but not all designers believe this is a good thing. A cabin house only increases reserve stability if it is impervious to flooding when submerged. If it has open hatches or has large windows and apertures that may break under pressure, it will only help a boat capsize and sink that much faster. The ISO formulas fail to take this into account and instead may award high stability ratings to motorsailers and deck-saloon boats with large houses and windows that may be vulnerable in extreme conditions.

Simplified Measures of Stability

In addition to developing stability curves, which obviously are fairly complex, designers and rating and regulatory authorities have also worked to quantify a boat’s stability with a single number. The simplest of these, the capsize screening value (CSV), was developed in the aftermath of the 1979 Fastnet Race. Over a third of the more than 300 boats entered in that race, most of them beamy, lightweight IOR designs, were capsized (rolled to 180 degrees) by large breaking waves, and this prompted a great deal of research on yacht stability. The capsize screening value, which relies only on published specifications and was intended to be accessible to laypeople, indicates whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions.

To figure out a boat’s CSV divide the cube root of its displacement in cubic feet into its maximum beam in feet: CSV = beam ÷ ³√DCF. You’ll recall that a boat’s weight and the volume of water it displaces are directly related, and that displacement in cubic feet is simply displacement in pounds divided by 64 (which is the weight in pounds of a cubic foot of salt water). To run an example of the equation, let’s assume we have a hypothetical 35-foot boat that displaces 12,000 pounds and has 11 feet of beam. To find its CSV, first calculate DCF–12,000 ÷ 64 = 187.5–then find the cube root of that result: ³√187.5 = 5.72; note that if your calculator cannot do cube roots, you can instead take 187.5 to the 1/3 power and get the same result. Divide that result into 11, and you get a CSV of 1.92: 11 ÷ 5.72 = 1.92.

Interpreting the number is also simple. Any result of 2 or less indicates a boat that is sufficiently self-righting to go offshore. The further below 2 you go, the more self-righting the boat is; extremely stable boats have values on the order of 1.7. Results above 2 indicate a boat may be prone to remain inverted when capsized and that a more detailed analysis is needed to determine its suitability for offshore sailing.

As handy as it is, the CSV has limited utility. It accounts for only two factors–displacement and beam–and fails to consider how weight is distributed aboard a boat. For example, if we load our hypothetical 12,000-pound boat with an extra 2,250 pounds for light coastal cruising, its CSV declines to 1.8. Load it with an extra 3,750 pounds for heavy coastal or moderate bluewater use, and the CSV declines still further, to 1.71. This suggests that the boat is becoming more stable, when in fact it may become less stable if much of the extra weight is distributed high in the boat.

Note too that a boat with unusually high ballast–including, most obviously, a boat with ballast in its bilges rather than its keel–will also earn a deceptively low screening value. Two empty boats of identical displacement and beam will have identical screening values even though the boat with deeper ballast will necessarily be more resistant to capsize.

Another single-value stability rating still frequently encountered is the IMS stability index number. This was developed under the IMS rating system to compare stability characteristics of race boats of various sizes. The formula essentially restates a boat’s AVS so as to account for its overall size, awarding higher values to longer boats, which are inherently more stable. IMS index numbers normally range from a little below 100 to over 140. For what are termed Category 0 races, which are transoceanic events, 120 is usually the required minimum. In Category 1 events, which are long-distances races sailed “well offshore,” 115 is the common minimum standard, and for Category 2 events, races of extended duration not far from shore, 110 is normally the minimum standard. Conservative designers and pundits often posit 120 as the acceptable minimum for an offshore cruising boat.

Since many popular cruising boats were never measured or rated under the IMS rule, you shouldn’t be surprised if you cannot find an IMS-based stability curve or stability index number for a cruising boat you are interested in. You may find one if the boat in question is a cruiser-racer, as IMS was once a prevalent rating system. Bear in mind, though, that the IMS index number does not take into account cabin structures (or cockpits, for that matter), and assumes a flush deck from gunwale to gunwale. Neither does it account for downflooding.

Another single-value stability rating that casts itself as an “index” is promulgated by the ISO. This is known as STIX, which is simply a trendy acronym for stability index. Because STIX values must be calculated for any new boat sold inside the European Union (EU), and because STIX is, in fact, the only government-imposed stability standard in use anywhere in the world, it is likely to become the predominant standard in years to come.

A STIX number is the result of many complex calculations accounting for a boat’s length, displacement, beam, ability to shed water after a knockdown, angle of vanishing stability, downflooding, cabin superstructure, and freeboard in breaking seas, among others. STIX values range from the low single digits to about 50. A minimum of 38 is required by the European Union for Category A boats, which are certified for use on extended passages more than 500 miles offshore where waves with a maximum height of 46 feet may be encountered. A value of at least 23 is required for Category B boats, which are certified for coastal use within 500 miles of shore where maximum wave heights of 26 feet may be encountered, and the minimum values for categories C and D (inshore and sheltered waters, respectively) are 14 and 5. These standards do not restrict an owner’s use of his boat, but merely dictate how boats may be marketed to the public.

The STIX standard has many critics, including many yacht designers who do not enjoy having to make the many calculations involved, but the STIX number is the most comprehensive single measure of stability now available. As such, it can hardly be ignored. Many critics assert that the standards are too low and that a number of 40 or greater is more appropriate for Category A boats and 30 or more is best for Category B boats. Others believe that in trying to account for and quantify so many factors in a single value, the STIX number oversimplifies a complex subject. To properly evaluate stability, they suggest, it is necessary to evaluate the various factors independently and make an informed judgment leavened by a good dose of common sense.

As useful as they may or may not be, STIX numbers are generally unavailable for boats that predate the EU’s adoption of the STIX standard in 1998. Even if you can find a number for a boat you are interested in, bear in mind that STIX numbers do not account for large, potentially vulnerable windows and ports in cabin superstructures, nor do they take into account a boat’s negative stability. In other words, boats that are nearly as stable upside down as right side up may still receive high STIX numbers.

The bottom line when evaluating stability is that no single factor or rating should be considered to the exclusion of all others. It is probably best, as the STIX critics suggest, to gather as much information from as many sources as you can, and to bear in mind all we have discussed here when pondering it.

Extremely good analysis of the issue. Did you do an engineering degree before law school Charlie? One more thought on stability that is outwith the scope of the indices. In the classic broach, as the vessel rounds up th keel bites the water and makes the turn worse, increasing the apparent wind and angle of heel, making the rudder progressively less effective,until it is powerless at 90 degrees heel. In a centreboarder with the board up, the bow skids off, avoiding a real broach, and hence danger of being forced to the spreaders hitting the water. We were caught in a 25 knot gust with our somewhat oversize spi up, the helmsman fell and let go, yet we never heeled past about 50 degrees. You had some fun on the cboard Che Vive in strong wind from aft. To some extent, this phenomenon mitigates the poorer AVS of the centreboarder. Is it enough? I hope to avoid checking it out in practice

@Neil: You’re right. I think centerboard boats are more stable in some situations, less stable in others, and the situations in which they are more stable are not represented in stability curves. It is an imperfect science, to say the least. For example, a point I probably should have emphasized a bit more strongly in the text is that the capsize screening value was never ever intended to be dispositive. It was only intended to identify boats that should be subjected to a more rigorous analysis. Thus the word “screening.” charlie

Charlie just came across this post while preparing for my next workshop this weekend. It’s flat out great, the best real world explanation of stability I’ve read.

John, Im John. I live in Rural N.C. about 75 minutes inland from New Bern. Im 58, single dad and when my 17 year old graduates next year i will be headed to Thailand….from North Carolina. I will NOT see the Cape to starboard…maybe i will write a book…Panama to Starboard

@John: Coming from you, that’s a real compliment. Thanks, mate!

A bit late in the day given the date of the article. Anyway here goes. The boat properties in this article are obtained under static equilibrium conditions. Thus the moment resistance curve is obtained by calculating the relative positions of the weight of the vessel and the buoyancy force as the hull is caused to rotate or heel- the resistance due to the moment produced by the misalignment of the two forces at various angles of heel. Because the movement takes place extremely slow no account is allowed for the effect of inertia. I would like to make my point my considering the example of a bag of sugar : In the first example (a) the sugar is gently poured from the bag onto the pan of a weigh scale until the required weight is reached , say one pound: thus an oz at a time until the scale pointer is at one pound ! In case (b) the sugar is placed in a bag, and the bag is placed in contact with the scale but then suddenly released. At which point the scale pointer will swing well past the 1 pound mark reaching 2 pounds , and the pointer will oscillate about the one pound mark, eventually coming to rest about this value! In case (c) the bag , instead of being placed in contact with pan is released from a height of one foot before being released. This will cause likely cause the pointer to be bent and a broken weigh scale.

It is a apparent that the properties used to measure a boats stability are derived from the conditions similar to case (a), while in reality they should be deduced from case (c) INERTIA IS IMPORTANT.

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Sail Far Live Free

Comfort, capsizing, and sailcalc.

"This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

Beam does enter into it as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch."

Very nice article to explain the "numbers". Your Irwin 28 shows as an excellent coastal cruiser from the "Good Old Boat" era. She has beautiful lines to me also-proportions look right and I am a big fan of a nice sheerline as I have been spoiled by my C&C25-MkI and sisterships 27 MkI-IV/30 MkI from the 70's-early 80's. Recently sold our C&C and looking for a coastal cruiser in the 28-3o ft range and did not have this on my list of prospects. One just popped up this week locally and I definitely want to see her. Thanks again for you articles-I am sure they have been and will be helpful to other new and salty sailors. Rob

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• Sailboat Guide

Calculations

Sail area / displacement ratio.

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

SA/D = SA ÷ (D ÷ 64) 2/3

• SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
• D : Displacement in pounds.

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Ballast / Displacement * 100

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

• D: Displacement of the boat in pounds.
• LWL: Waterline length in feet

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 )

• D: Displacement of the boat in pounds
• LOA: Length overall in feet
• Beam: Width of boat at the widest point in feet

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

CSV = Beam ÷ ³√(D / 64)

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL

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Sailboat Specifications 101: Explained For Beginners

As a newbie to sailing, the sailboat specifics can be overwhelming. Taking time to familiarize yourself with the measurements and vocabulary associated with boats will allow you to be more informed about boats and know which type is right for which activity. You’ll be a better sailor and boater with this knowledge.

Table of Contents

LOA – Length Overall

Length Overall (LOA) is the most common measurement used to describe the size of a sailboat. It refers to the total length of the vessel, from the tip of the bow (front) to the aft end of the stern (back).

LOA is typically measured in feet or meters. This measurement can be useful when comparing boats of similar types, as it gives you an idea of the overall size.

LOD-length on deck

LOD, or Length on Deck, is the measurement of the boat from the tip of the bow to the stern along the deck.

This length does not include any spars, bowsprits, antennas, etc. that are mounted above the main deck.

The difference between LOD and LOA (length overall) is that LOA takes into account any protrusions such as spars and bowsprits. LOD may be shorter than LOA sometimes.

LWL – Load Waterline Length

The LWL or Load Waterline Length is the measurement of the length of a boat at the point where it touches the water.

It is the length of the boat that makes contact with the water and is often shorter than the overall length (LOA) due to the curvature of the hull.

The LWL plays an important role in determining the performance of a sailboat; for example, a longer LWL can help increase stability and reduce drag, allowing the boat to move more efficiently through the water.

The LWL also affects the size of the sail area needed to power the boat. As such, boats with a longer LWL will require larger sails to generate adequate power, while boats with a shorter LWL may need smaller sails.

Beam – The width of the boat

The beam of a sailboat is the maximum width of the hull and is an important measurement for sailing performance.

A wider beam provides more stability on the water and increases the overall sail area. Having a larger sail area will help to increase speed and maneuverability in windy conditions.

It’s important to consider the beam of the boat when deciding what type of sails to use. A boat with a wider beam will require bigger sails, while a boat with a narrower beam will require smaller sails.

Draft – The depth of the boat in the water

Draft measures the distance from the waterline to the lowest point of the boat’s hull when it is fully loaded.

This is important because it affects the boat’s maneuverability, stability, and performance in different sea conditions.

It also affects the sail area of the boat, since a greater draft can provide more stability and lift, allowing for larger sails to be used. Shallow draft boats tend to be able to get into shallower waters than those with deeper drafts.

Full keel vs. modified keel vs. fin keel

The three main types of keels are full, modified, and fin keels.

Full keels are the oldest and most traditional type of keel. They are typically found on heavier displacement boats such as cruisers and larger sailboats.

Full keels provide more stability due to their size and weight, but also create more drag, which can slow down the boat.

Modified keels are a hybrid between full and fin keels. They are often used on boats with moderate displacement, meaning they have a moderate amount of weight.

Modified keels provide a good balance of stability and speed due to their shape and size.

Finally, fin keels are usually found on lighter displacement boats such as racing and performance sailboats.

Fin keels have the least amount of drag, allowing the boat to move faster, but they are not as stable as full or modified keels.

Displacement – The weight of the boat

The displacement of a boat refers to the total weight of the boat, including all of the materials used to construct it. It is usually measured in either metric tonnes or long tons.

The type of displacement your boat has will depend on its size and purpose, with light displacement boats usually being used for day sailing and racing, while moderate and heavy displacement boats are better suited for coastal and ocean cruising.

Light displacement boats are typically quite lightweight, with a hull weight of around 2 tonnes and a total weight of 4 tonnes or less.

These boats are often very fast and agile but can have limited load-carrying capacity due to their light construction.

Moderate displacement boats typically weigh between 4 and 10 tonnes, with a hull weight ranging from 3 to 8 tonnes.

These boats are best suited for coastal cruising and are usually made from heavier materials than light displacement boats. This makes them able to carry a greater load and handle rougher seas with more confidence.

Heavy displacement boats weigh more than 10 tonnes, with a hull weight of up to 15 tonnes.

These boats are built for long-distance ocean cruising and are designed to be sturdy and reliable even in heavy weather. As such, they are usually made from stronger materials than other types of boats and have a much larger load-carrying capacity.

D/L or DLR ratio- Displacement to length ratio

Displacement to length ratio (DLR) is a calculation used to measure the size of a sailboat.

It is determined by dividing the displacement (the weight of the boat) by the waterline length (the length of the boat that is in contact with the water when it is afloat).

The result of this calculation, also known as the DLR, can be used to compare different types of boats or to determine which type of sailboat is most suitable for specific conditions.

The formula for calculating the displacement-to-length ratio is: DLR = (Displacement/2240)/(0.01xLWL)^3 Displacement in pounds, LWL is Waterline Length in feet

Generally, sailboats with higher DLRs tend to have a more rounded hull shape and are better suited to deep-water sailing in heavy weather conditions.

Sailboats with lower DLRs tend to have a more slender hull shape and are better suited to shallow water sailing in light weather conditions.

Ballast is the weight of the boat that is not part of the boat’s structure. This weight can come from a lead, water, or other materials, and it is located in the bottom of the boat to help keep it stable in the water.

The amount of ballast affects the sail area, as more ballast will lower the sail area while decreasing ballast will increase the sail area.

This is because when there is more ballast in the boat, it will be pushed down into the water which reduces the area that a sail can reach. On the other hand, decreasing ballast will allow a sail to extend further.

Ballast is also important for maneuverability and stability; too much ballast and the boat will be sluggish and difficult to turn, while too little ballast could cause the boat to be unstable and even capsize.

Balancing the amount of ballast is key to achieving optimal performance for any type of sailboat.

CSF-Capsize screening formula

The capsize screening formula is a calculation that provides a good indication of the stability of a sailboat. It is the ratio of a boat’s displacement (weight) to its Beam (width).

Capsize ratio formula: Beam / ((Displacement/64.2)1/3) The beam is in feet. Displacement is in pounds

A good capsize ratio is generally considered to be between 1.33 and 2.0, although this can vary depending on the type of boat and its purpose.

A lower capsize ratio indicates that the boat is more stable, as it will be less likely to tip over in strong winds or waves. A higher capsize ratio indicates that the boat is more prone to capsizing.

Motion comfort ratio

Motion comfort ratio (also referred to as “Ted Brewer” ratio) is a measure of the overall stability of a sailboat.

Generally, a boat with a motion comfort ratio greater than 40 is considered stable and a boat with a motion comfort ratio less than 30 is considered unstable.

A boat with a motion comfort ratio between 30-40 is considered moderately stable. The higher the motion comfort ratio, the more comfortable the boat will be in rough waters.

Ted Brewer’s CR formula is: Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x Beam 1.333 ).

For instance, a boat with an LWL of 35 ft and a displacement of 10,000 lbs would have a motion comfort ratio of 37.5. This would indicate that the boat is moderately stable and should provide an adequate level of comfort in rough waters.

The motion comfort ratio was developed by Ted Brewer and has been used for many years as an indication of a boat’s stability.

It is important to keep in mind, however, that this ratio alone cannot give an accurate picture of how stable a boat is. Other factors such as hull type and keel type should also be taken into account when assessing a boat’s stability.

Ballast to displacement ratio

The ballast-to-displacement ratio is a measure of how much ballast is needed in relation to the weight of the boat.

The higher the ballast-to-displacement ratio, the more stable the boat will be and the less likely it will be to capsize.

the ballast-to-displacement ratio is important for ensuring the boat is adequately balanced and has good performance when sailing.

It is especially important for boats that have large sail areas, as larger sail areas require more ballast to keep the boat steady.

When considering a boat’s ballast-to-displacement ratio, keep in mind that a ratio of 40-50% is generally considered to be optimal. Any higher than that may be too much, while any lower may not be enough.

How Often Do Sailboats Capsize: A Comprehensive Guide

Table of Contents

Introduction

1. Understanding Sailboat Stability

Before we dive into the topic of sailboat capsizing, it’s essential to grasp the concept of sailboat stability. Sailboats rely on a delicate balance between buoyancy, the shape of their hulls, and the distribution of weight. This equilibrium ensures that the boat remains upright and maintains its stability while maneuvering through water.

2. Factors Contributing to Sailboat Capsizing

Several factors can contribute to sailboat capsizing. Understanding these factors will help sailors make informed decisions to minimize the risk of capsizing incidents.

Weather Conditions

Adverse weather conditions, such as strong winds, high waves, and sudden storms, pose a significant risk to sailboats. Powerful gusts can exert excessive force on the sails, causing the boat to tip over or capsize. It’s crucial for sailors to monitor weather forecasts and avoid venturing into hazardous conditions.

Design and Stability Characteristics

The design and stability characteristics of a sailboat play a crucial role in its resistance to capsizing. Factors such as hull shape, keel design, and ballast contribute to a boat’s stability. Sailboats with deep keels and a low center of gravity are generally more stable and less prone to capsizing.

Improper Handling and Operator Error

Inexperienced sailors or those who fail to adhere to proper handling techniques are at a higher risk of capsizing their sailboats. Incorrect sail trim, excessive heeling, abrupt maneuvers, or overloading the boat can destabilize the vessel, leading to a capsize. It is essential for sailors to receive proper training and practice good seamanship.

3. Statistics on Sailboat Capsizing

To gain a better understanding of the frequency of sailboat capsizing, let’s explore some relevant statistics.

Global Incident Rates

Accurate global incident rates for sailboat capsizing are challenging to determine due to underreporting and varying definitions of “capsizing.” However, it is evident that capsizing incidents occur across different bodies of water worldwide.

Types of Sailboats Most Prone to Capsizing

Certain types of sailboats are more susceptible to capsizing than others. Small, lightweight dinghies and high-performance racing sailboats are more likely to capsize due to their design and the nature of their intended use. Larger cruising sailboats with keels and more stability tend to have a lower risk of capsizing.

Capsizing Incidents and Fatalities

While the majority of sailboat capsizing incidents do not result in fatalities, it is crucial to prioritize safety and minimize the risks involved. Fatalities can occur in extreme weather conditions or when proper safety measures are not followed.

4. Preventive Measures and Safety Tips

To reduce the likelihood of sailboat capsizing and ensure a safe sailing experience, consider the following preventive measures and safety tips:

Checking Weather Conditions

Always check weather forecasts before setting sail. Avoid venturing into adverse weather conditions, such as high winds or storms. Stay informed and have a backup plan if conditions worsen unexpectedly.

Proper Boat Maintenance and Rigging

Regular maintenance of your sailboat is essential for its seaworthiness. Inspect the rigging, sails, and hull for any signs of wear or damage. Ensure that all components are properly rigged and in good working condition.

Adequate Training and Experience

Obtain adequate training and gain experience before setting out on the open water. Learn the basics of sailing, including boat handling, navigation, and understanding weather patterns. Consider taking sailing courses or joining a sailing club to enhance your skills.

Safety Equipment and Emergency Preparedness

Equip your sailboat with essential safety equipment, including life jackets, flares, a first aid kit, and a functioning VHF radio. Familiarize yourself with emergency procedures and ensure that everyone on board knows how to use the safety equipment.

Understanding Sailboat Limits and Operating within Them

Every sailboat has its limits. Understand the capabilities and limitations of your boat, especially regarding wind conditions and weight capacity. Avoid overloading the boat and be mindful of the sailboat’s stability characteristics.

5. Conclusion

Sailboat capsizing is a concern for sailors worldwide. However, with proper knowledge, preparation, and adherence to safety guidelines, the risk of capsizing incidents can be significantly reduced. Understanding sailboat stability, recognizing contributing factors, and implementing preventive measures will ensure a safer and more enjoyable sailing experience for all enthusiasts.

Frequently Asked Questions (FAQs)

1. is capsizing a common occurrence for sailboats.

Capsizing incidents are relatively rare, especially when considering the vast number of sailboats worldwide. However, it is crucial to prioritize safety and take measures to minimize the risk of capsizing.

2. Are smaller sailboats more likely to capsize?

Yes, smaller sailboats, such as dinghies, tend to be more prone to capsizing due to their lightweight construction and design characteristics. However, proper handling and adherence to safety guidelines can mitigate the risk.

3. Can a sailboat capsize in calm weather conditions?

While capsizing is more commonly associated with adverse weather conditions, it is possible for a sailboat to capsize even in calm weather. Improper handling or operator error can destabilize the boat, leading to a capsize.

4. What should I do if my sailboat capsizes?

If your sailboat capsizes, remain calm and follow proper safety procedures. Stay with the boat, as it provides flotation. Signal for help if needed and follow appropriate rescue techniques.

5. Are there any specialized courses for learning how to prevent sailboat capsizing?

Yes, there are various sailing courses available that focus on safety and preventing capsizing incidents. These courses cover topics such as seamanship, boat handling techniques, and understanding weather conditions.

In conclusion, understanding the factors contributing to sailboat capsizing, maintaining proper sailboat stability, and following preventive measures are key to enjoying a safe and adventurous sailing experience. While sailboat capsizing incidents may occur, they can be minimized through knowledge, experience, and preparedness. By checking weather conditions, maintaining the sailboat, receiving adequate training, equipping with safety gear, and understanding the boat’s limits, sailors can navigate the waters with confidence. Remember, safety should always be a top priority to ensure a memorable and incident-free sailing journey.

Mark Alexander Thompson

Mark Alexander Thompson is a seasoned sailor with over five years of experience in the boating and yachting industry. He is passionate about sailing and shares his knowledge and expertise through his articles on the sailing blog sailingbetter.com. In his free time, Mark enjoys exploring new waters and testing the limits of his sailing skills. With his in-depth understanding of the sport and commitment to improving the sailing experience for others, Mark is a valuable contributor to the sailing community.

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Engineering:Capsize screening formula

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The capsize screening formula (CSF) is a controversial method of establishing the ability of boats to resist capsizing. It is defined for sailboats as: Beam / (( Displacement /64.2) 1/3 ), with Displacement measured in pounds, and Beam in feet. A lower figure supposedly indicates greater stability, however the calculation does not consider factors such as hull shape or ballast.

The formula came into being after the 1979 Fastnet race in England where a storm shredded the race fleet. The Cruising Club of America (CCA) put together a technical committee that analyzed race boat data. They came up with the formula to compare boats based on readily available data. The CCA characterizes the formula as "rough".

A lower value is supposed to indicate a sailboat is less likely to capsize. A value of 2 is taken as a cutoff for acceptable to certain race committees. However this is an arbitrary cutoff based on the performance of boats in the 1979 Fastnet race. The CSF does not consider the hull shape or ballast location.

Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast in a bulb at the bottom of an eight foot fin keel , the other could have a heavy hull with 20% ballast in a 2-foot-deep (0.61 m) full-length keel . The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.

• Davis, Stephen L. Desirable and Undesirable Characteristics of the Offshore Yachts , W.W. Norton, 1987.
• Howard, J. Handbook of Offshore Cruising: The Dream and Reality of Modern Ocean Cruising , Sheridan House, 2000.
• Rousmaniere, John. Fastnet Force 10 , Nautical Publishing, 1980.
• Vigor, John. The Practical Mariner's Book of Knowledge , McGraw-Hill Professional, 1994.

External links

• Capsize formula for displacement sailboats.
• Designed For Safety: Choosing a safe Boat @boats.com
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Indonesia rescuers save 69 Rohingya refugees at sea

MEULABOH, Indonesia - Dozens of Rohingya refugees stranded on the rusty hull of a capsized ship were rescued on March 21 after the dehydrated and sunburnt group had drifted at sea for more than a day.

The group comprised 69 men, women and children, some of whom had been at sea for weeks on a rickety wooden boat from squalid camps in Bangladesh, where many of the heavily persecuted Myanmar minority have fled.

The reddish hull of the vessel poking out of the water was their only refuge after their wooden boat and another vessel trying to help them both capsized on March 20.

The second boat, belonging to local fishermen, overturned when the refugees tried to climb on in a panic.

“Why did the boat capsize? There was heavy rain,” said a 27-year-old survivor who gave his name as Dostgior in broken Indonesian.

Survivors estimated 150 Rohingya had been on board, with dozens swept away, according to local fishermen and the United Nations High Commission for Refugees (UNHCR), in what would represent another tragedy at sea for the heavily persecuted Myanmar minority.

The number of victims rescued alive is 69, the local search and rescue agency said in a statement, comprising nine children, 42 men and 18 women.

Footage from the boat seen by AFP showed men, women and children being taken to safety by the local search and rescue agency.

“I’d been at sea for 15 days, but there are others here who have been here longer than that. Some have been here for a month,” said Mr Dostgior.

He said he had travelled from Cox’s Bazar in Bangladesh, where many Rohingya have fled persecution and were living in squalid camps.

“In Bangladesh, I met someone who could take me to Indonesia. My goal in going to Indonesia is to pay someone to take me to Malaysia. Once in Malaysia, I will pay someone else to enter,” he told AFP.

Many Rohingya make the perilous 4,000km journey from Bangladesh to Malaysia, fuelling a multimillion-dollar human-smuggling operation that often involves stopovers in Indonesia.

The authorities took the group to shore in the West Aceh capital, Meulaboh, on March 21, the local search and rescue agency said.

They were met at Meulaboh port by 10 ambulances and medics, which whisked some of the refugees to hospital while others were taken to a temporary shelter at an old Red Cross building in a nearby village, said an AFP journalist.

But locals in Beureugang village launched a protest against the refugees staying there and unfurled a banner that read: “We reject the Rohingya refugees.”

Some Rohingya boats landing in Aceh in recent months have been pushed back out to sea as sentiment towards the minority group shifts in the ultra-conservative Indonesian province.

Many Acehnese, who themselves have memories of decades of bloody conflict, are sympathetic to the plight of their fellow Muslims.

But others say their patience has been tested, claiming the Rohingya consume scarce resources and occasionally come into conflict with locals.

Some of the refugees said they were from Myanmar and had tried to reach Thailand but were rejected, West Aceh fishing community secretary-general Pawang Amiruddin told AFP on March 20.

On March 20, six Rohingya from the same vessel were rescued by fishermen .

One of those survivors said around 50 refugees had been swept away by currents and were missing or feared dead.

“He said the boat took 151 people. Once the boat capsized, approximately around 50 people may be missing and passed away,” UNHCR protection associate Faisal Rahman said.

“We are still coordinating with respective government agencies to do our best to save as many lives as possible.”

From mid-November to late January, 1,752 refugees, mostly women and children, landed in the Indonesian provinces of Aceh and North Sumatra, according to UNHCR. Hundreds remain in shelters.

The agency said it was the biggest influx into the Muslim-majority country since 2015. AFP

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Boats with Rohingya refugees capsize off Indonesia

• The UN refugee agency is calling for search and rescue efforts
• The UNHCR estimates about 2,000 Rohingya have reached Indonesia since last October

A boat carrying Rohingya refugees and a fishing boat trying to help them capsized in waters off Indonesia's westernmost coast on Wednesday, with six people rescued and some carried away by strong currents, local fishermen said.

The mostly Muslim Rohingya are heavily persecuted in Myanmar, and thousands risk their lives each year on long and expensive sea journeys, often in flimsy boats, to try to reach Malaysia or Indonesia.

“We received a report from fishermen in West Aceh that a boat carrying Rohingya refugees capsized in the sea near Meulaboh. A fisherman saw the Rohingyas at 0100 GMT with their boat sinking,” Nanda Ferdiansyah from West Aceh traditional fishing community told AFP.

“As soon as the fisherman's boat approached them, they all got on the boat. As soon as they got onboard, the fisherman's boat also sank because of overcapacity.”

The Rohingya boat had capsized about 11 kilometres off Kuala Bubon beach in West Aceh, its fishing community's secretary general Pawang Amiruddin said in a statement. 

“The report from local fishermen said a Rohingya boat capsized and they (the refugees) saved themselves by getting onto the hull of the overturned boat. Some other people were carried away by the strong currents,” the statement said.

“So far six people have been rescued by the local fisherman, four women and two men.”

It did not say if those carried away were feared to have died. The United Nations refugee agency said it was “deeply concerned” about the reports of the incident, saying “tens of Rohingya refugees” were in desperate need of rescue but could not confirm exact numbers.

“We hope that search and rescue could be performed and the refugees can be brought to land as soon as possible. This is an emergency,” UNHCR said in a statement.

Local police and the regional government did not respond to requests for comment. The incident comes after months of Rohingya arrivals on Indonesian shores. 

From mid-November to late January, 1,752 refugees -- mostly women and children -- landed in the Indonesian provinces of Aceh and North Sumatra, according to UNHCR. The agency said it was the biggest influx into the Muslim-majority country since 2015.

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Indonesian fishermen rescue dozens of Rohingya after boat capsizes

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Citing safety risk, Taiwan recommends president does not visit South China Sea

Taiwan's top security official said on Thursday he does not currently recommend President Tsai Ing-wen visit the South China Sea given the possible risk to her flight from "interference by relevant countries" given China's military presence there.

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Rowing boats capsize near Connecticut

Posted: March 21, 2024 | Last updated: March 21, 2024

Nearly 30 members of a rowing club in Connecticut were rescued from the Long Island Sound on Wednesday when their boats capsized.

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NEWS... BUT NOT AS YOU KNOW IT

Nearly 1,000 tonnes of acid has just fallen into the sea after tanker capsized

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Eight people have died after a South Korean chemical tanker capsized off an island in south-western Japan .

The tanker was carrying 980 tonnes of acrylic acid, a corrosive compound used in adhesives, paints and polishes.

One crew member survived and was rescued, with another two unaccounted for after the vessel capsized.

The Japanese coast guard said it received a distress call from the chemical tanker Keoyoung Sun, saying that it was tilting while seeking refuge from bad weather near Japan’s Mutsure Island, about 620 miles from Tokyo.

The ship was completely capsized by the time rescuers arrived at the scene, with footage on NHK showing the ship lying upside down as the sea washed over it.

No leak has been detected from the chemical tanks but officials are studying what environmental protection measures may be needed.

The ship was carrying 11 crew, of whom nine have been found, authorities said.

The one crew member confirmed alive is from Indonesia, with the coast guard still searching for two more.

South Korean officials have held a meeting to discuss the incident as vice foreign minister Kang Insun asked officials to mobilise all available resources to support rescue works.

He’s also asked officials to assist the relatives of South Korean crew members, according to the foreign ministry.

The ship was en route from the Japanese port of Himeji to Ulsan in South Korea, the coast guard said.

Its captain was South Korean, and its crew included another South Korean national, a Chinese national and eight Indonesians, according to the coast guard.

In November last year, a cargo ship split in half during a violent storm in the Black Sea, killing nine.

The Turkish-flagged Kafkametler sank off the coast of Eregli, northern Turkey after smashing into a breakwater several times, officials said.

Get in touch with our news team by emailing us at [email protected] .

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