best lightning protection for sailboat

Yachting Monthly

• Digital edition

Sailing in lightning: how to keep your yacht safe

• In partnership with Katy Stickland
• July 22, 2022

How much of a concern is a lightning strike to a yacht and what can we do about it? Nigel Calder looks at what makes a full ‘belt and braces’ lightning protection system

Storm clouds gather at Cowes, but what lightning protection system, if any, does your boat have for anchoring or sailing in lightning? Credit: Patrick Eden/Alamy Stock Photo

Most sailors worry about sailing in lightning to some extent, writes Nigel Calder .

After all, going around with a tall metal pole on a flat sea when storm clouds threaten doesn’t seem like the best idea to most of us.

In reality, thunder storms need plenty of energy, driven by the sun, and are much less frequent in northern Europe than in the tropics.

However, high currents passing through resistive conductors generate heat.

Small diameter conductors melt; wooden masts explode; and air gaps that are bridged by an arc start fires.

Sailing in lightning: Lightning is 10 times more likely over land than sea, as the land heats up more than water, providing the stronger convection currents needed to create a charge. Credit: BAE Inc/Alamy Stock Photo

On boats, radio antennas may be vaporised, and metal thru-hulls blown out of the hull, or the surrounding fiberglass melted, with areas of gelcoat blown off.

Wherever you sail, lightning needs to be taken seriously.

Understanding how lightning works, will help you evaluate the risks and make an informed decision about the level of protection you want on your boat and what precautions to take.

Most lightning is what’s called negative lightning, between the lower levels of clouds and the earth. Intermittent pre-discharges occur, ionising the air.

Whereas air is normally a poor electrical conductor, ionised air is an excellent conductor.

These pre-discharges (stepped leaders) are countered by a so-called attachment spark (streamer), which emanates from pointed objects (towers, masts, or lightning rods) that stand out from their surroundings due to their height.

Summer is the season for lightning storms in the UK. Here, one finds early at Instow, Devon. Credit: Terry Matthews/Alamy Stock Photo

This process continues until an attachment spark connects with a stepped leader, creating a lightning channel of ionised air molecules from the cloud to ground.

The main discharge, typically a series of discharges, now takes place through the lightning channel.

Negative lightning bolts are 1 to 2km (0.6 to 1.2 miles) long and have an average current of 20,000A.

Positive lightning bolts are much rarer and they can have currents of up to 300,000A.

Preventing damage when sailing in lightning

A lightning protection system (LPS) is designed to divert lightning energy to ground (in this case the sea), in such a way that no damage occurs to the boat or to people.

Ideally, this also includes protecting a boat’s electrical and electronic systems, but marine electronics are sensitive and this level of protection is hard to achieve.

Lightning protection systems have two key components: First, a mechanism to provide a path with as little resistance as possible that conducts a lightning strike to the water.

This is established with a substantial conductor from an air-terminal to the water.

Components of an external and internal lightning protection system. Credit: Maxine Heath

This part of the LPS is sometimes called external lightning protection.

Second, a mechanism to prevent the development of high voltages on, and voltage differences between, conductive objects on the boat.

This is achieved by connecting all major metal objects on and below deck to the water by an equipotential bonding system.

Without this bonding system high enough voltage differences can arise on a boat to develop dangerous side flashes.

The bonding system can be thought of as internal lightning protection.

Rolling ball concept

Lightning standards, which apply ashore and afloat, define five lightning protection ‘classes’, ranging from Class V (no protection) to Class I.

There are two core parameters: the maximum current the system must be able to withstand, which determines the sizing of various components in the system, and the arrangement and number of the air terminals, aka lightning rods.

Let’s look at the arrangement of the air terminals first. It is best explained by the rolling ball concept.

A lightning strike is initiated by the stepped leaders and attachment sparks connecting to form the lightning channel.

The distance between the stepped leader and the attachment sparks is known as the breakdown distance or striking distance.

If we imagine a ball with a radius equal to the striking distance, and we roll this ball around an object to be protected, the upper points of contact define the possible lightning impact points that need to be protected by air terminals.

Lightning protection theories and classifications rely on a ‘rolling ball’ concept to define requirements, areas of risk and protected areas. Credit: Maxine Heath

The air terminal will theoretically provide a zone of protection from the point at which the terminal connects with the circumference of the rolling ball down to the point at which that circumference touches the water.

The shorter the striking distance, the less the radius of the rolling ball and the smaller the area within the protection zone defined by the circumference of the rolling ball.

The smaller the protection zone, the more air terminals we need. So, we use the shortest striking distance to determine the minimum number and location of air terminals.

Class I protection assumes a rolling ball radius of 20m; Class II assumes a rolling ball radius of 30m.

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Boat building standards are based on a striking distance/rolling ball radius of 30m (Class II).

For masts up to 30m above the waterline, the circumference of the ball from the point at which it contacts the top of the mast down to the water will define the zone of protection.

For masts higher than 30m above the waterline, the ball will contact the mast at 30m and this will define the limit of the zone of protection.

If Class I protection is wanted, the radius of the ball is reduced to 20m, which significantly reduces the zone of protection and, on many larger recreational boats, may theoretically necessitate more than one air terminal.

Protection classes

With most single-masted monohull yachts, an air terminal at the top of the mast is sufficient to protect the entire boat to Class I standards.

The circumference of the rolling ball from the tip of the mast down to the surface of the water does not intercept any part of the hull or rig.

However, someone standing on the fore or aft deck might have the upper part of their body contact the rolling ball, which tells us this is no place to be in a lightning storm.

Some boats have relatively high equipment or platforms over and behind the cockpit.

Protection classes to protect your boat while anchored or sailing in lightning

These fittings and structures may or may not be outside the circumference of the rolling ball.

Once again, this tells us to avoid contact with these structures during a lightning storm.

Ketch, yawl, and schooner rigged boats generally require air terminals on all masts, except when the mizzen is significantly shorter than the main mast.

The external LPS

The external LPS consists of the air terminal, a down conductor, and an earthing system – a lightning grounding terminal.

The down conductor is also known as a primary lightning protection conductor.

All components must be sized to carry the highest lightning peak current corresponding to the protection class chosen.

In particular, the material and cross-sectional area of the air terminal and down conductor must be such that the lightning current does not cause excessive heating.

The air terminal needs to extend a minimum of 150mm above the mast to which it is attached.

A graph depicting NASA’s record of yearly global lightning events. The Congo once recorded more than 450 strikes per km2

It can be a minimum 10mm diameter copper rod, or 13mm diameter aluminum solid rod.

It should have a rounded, rather than a pointed, top end.

VHF antennas are commonly destroyed in a lightning strike.

If an antenna is hit and is not protected by a lightning arrestor at its base, the lightning may enter the boat via the antenna’s coax cable.

A lightning arrestor is inserted in the line between the coax cable and the base of the antenna.

It has a substantial connection to the boat’s grounding system, which, on an aluminum mast, is created by its connection to the mast.

In normal circumstances, the lightning arrestor is nonconductive to ground.

When hit by very high voltages it shorts to ground, in theory causing a lightning strike to bypass the coax – although the effectiveness of such devices is a matter of some dispute.

Down conductors

A down conductor is the electrically conductive connection between an air terminal and the grounding terminal.

For many years, this conductor was required to have a resistance no more than that of a 16mm² copper conductor, but following further research, the down conductor is now required to have a resistance not greater than that of a 20mm² copper conductor.

For Class I protection, 25mm² is needed. This is to minimise heating effects.

Let’s say instead we use a copper conductor with a cross-sectional area of 16mm² and it is hit by a lightning strike with a peak current corresponding to Protection Class IV.

Sailing in lightning: This catamaran relies upon cabling to ground from the shrouds but stainless steel wire is not a good enough conductor. Credit: Wietze van der Laan

The conductor will experience a temperature increase of 56°C. A 16mm² conductor made of stainless steel (for example, rigging ) will reach well over 1,000°C and melt or evaporate.

Shrouds and stays on sailboats should be connected into a LPS only to prevent side flashes.

The cross-sectional area of the metal in aluminum masts on even small sailboats is such that it provides a low enough resistance path to be the down conductor.

Whether deck- or keel-mounted, the mast will require a low resistance path, equivalent to a 25mm² copper conductor, from the base of the mast to the grounding terminal.

Grounding terminal

Metal hulled boats can use the hull as the grounding terminal. All other boats need an adequate mass of underwater metal.

In salt water this needs a minimum area of 0.1m². In fresh water, European standards call for the grounding terminal to be up to 0.25m².

A grounding terminal must be submerged under all operating conditions.

An external lead or iron keel on monohull sailing boats can serve as a grounding terminal.

This owner of this Florida-based yacht decided to keep the keel out of the equation when is came to a grounding plate. High electrical currents don’t like sharp corners, so a grounding plate directly beneath the mast makes for an easier route to ground. Credit: Malcolm Morgan

In the absence of a keel , the cumulative surface area of various underwater components – propellers, metal thru-hulls, rudders – is often more than sufficient to meet the area requirements for a grounding terminal.

However, these can only be considered adequate if they are situated below the air terminal and down conductor and individually have the requisite surface area.

Metal through-hulls do not meet this requirement.

If underwater hardware, such as a keel, is adequate to be used as the grounding terminal, the interconnecting conductor is part of the primary down conductor system and needs to be sized accordingly at 25mm².

Propellers and radio ground plates

Regardless of its size, a propeller is not suitable as a grounding terminal for two reasons.

First, it is very difficult to make the necessary low-resistance electrical connection to the propeller shaft, and second, the primary conductor now runs horizontally through the boat.

The risk of side flashes within the boat, and through the hull to the water is increased.

Sailing in lightning: GRP hull, fairing filler and iron keel will have carried different voltages during the strike – hence this damage

An engine should never be included in the main (primary) conducting path to a grounding terminal.

On modern engines, sensitive electronic controls will be destroyed in a lightning strike, and on all engines, oil in bearings and between gears will create resistance and therefore considerable heat which is likely to result in internal damage.

However, as it is a large conductive object, the engine should be connected to the internal lightning protection system.

Internal lightning protection

On its way to ground, lightning causes considerable voltage differences in adjacent objects – up to hundreds of thousands of volts.

This applies to boats with a functioning external lightning protection system but without internal protection.

Although the lightning has been given a path to ground along which it will cause as little damage as possible, dangerous voltages can be generated elsewhere, resulting in arcing and side flashes, threatening the boat and crew, and destroying electronic equipment.

We prevent these damaging voltage differences from arising by connecting all substantial metal objects on the boat to a common grounding point.

One of the holy grails of marine photography – a direct lightning strike on a yacht’s mast. Credit: Apex

The grounding terminal is also wired to the common grounding point.

By tying all these circuits and objects together we hold them at a common voltage, preventing the build-up of voltage differences between them.

All conductive surfaces that might be touched at the same time, such as a backstay and a steering wheel, need to be held to the same voltage.

If the voltages are the same, there will be no arcing and no side flashes.

The bonding conductors in this internal LPS need to be stranded copper with a minimum size of 16mm².

Note that there can be bonding of the same object for corrosion prevention, lightning protection, and sometimes DC grounding.

We do not need three separate conductors.

Electronic Device Protection

With lightning protection systems, we need to distinguish electric circuit and people protection from device protection.

Even with an internal LPS, high induced voltages may occur on ungrounded conductors (such as DC positive) which will destroy any attached electronics.

A mechanism is needed to short high transient voltages to ground.

This is done with surge protection devices (SPD), also known as transient voltage surge suppressors (TVSS) or lightning arrestors.

Marine-specific SPDs are few in number and domestic models are not suitable for boats

In normal circumstances these devices are non-conductive, but if a specified voltage – the clamping voltage – is exceeded they divert the spike to ground.

There are levels of protection defined in various standards depending on the voltages and currents that can be handled, the speed with which this occurs, and other factors.

This is a highly technical subject for which it is advisable to seek professional support.

Most SPDs are designed for AC circuits.

When it comes to DC circuits there are far fewer choices available to boat owners although there are an increasing number for solar installations that may be appropriate.

There is no such thing as a lightning-proof boat, only a lightning-protected boat, and for this there needs to be a properly installed LPS.

Nigel Calder is a lifelong sailor and author of Boatowner’s Mechanical and Electrical Manual. He is involved in setting standards for leisure boats in the USA

Even so, in a major strike the forces involved are so colossal that no practical measures can be guaranteed to protect sensitive electronic equipment.

For this, protection can be provided with specialised surge protection devices (SPDs).

The chances of a direct lightning strike on a yacht are very small, and the further we are north or south of the equator, the smaller this chance becomes.

It’s likely your chances of receiving a direct lightning strike are very much higher on a golf course than at sea.

‘Bottle brush’-type lightning dissipators are claimed by sellers to make a boat invisible to lightning by bleeding off static electrical charge as it builds up.

The theory rests upon the concept that charged electrons from the surface of the earth can be made to congregate on a metal point, where the physical constraints caused by the geometry of the point will result in electrons being pushed off into the surrounding atmosphere via a ‘lightning dissipator’ that has not just one point, but many points.

It is worth noting that the concept has met with a storm of derision from many leading academics who have argued that the magnitude of the charge that can be dissipated by such a device is insignificant compared to that of both a cloud and individual lightning strikes.

It seems that the viable choices for lightning protection remain the LPS detailed above, your boatbuilder’s chosen system (if any), or taking one’s chances with nothing and the (reasonable) confidence that it’s possible to sail many times round the world with no protection and suffer no direct strikes.

Whichever way you go, it pays to stay off the golf course!

Enjoyed reading Sailing in lightning: how to keep your yacht safe?

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Modern Lightning Protection On Recreational Watercraft

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While you can't prevent a strike, there's a lot you can do to mitigate — or even prevent — damage.

A thunderstorm passing over a marina has the potential to cause expensive damage.

The recent advances in electrical and electronic systems have revolutionized recreational boating. Vessel operations have been simplified and the boating experience enhanced due to the integration of electronics into almost every onboard system, from navigation and communications to propulsion and maneuvering. Complex engine electronics known by various names including Engine Control Unit (ECU) and Engine Control Module (ECM) have increased performance and reduced emissions on modern engines. However, these advances have come at a cost. Many 21st-century boaters depend on electronic systems to navigate and maneuver their boats, and many modern engines will not function if their electronics are compromised. That makes modern mariners and their boats vulnerable to a lightning strike that damages these now mission-critical systems, potentially leaving the boat dead in the water without navigation or communications equipment.

Unfortunately, sensitive electronics on boats have become increasingly vulnerable to lightning strikes, yet lightning-protection systems have not kept pace. It's not that there haven't been significant advances in lightning science since Benjamin Franklin developed his theories on how to protect barns and livestock. The National Fire Protection Association, Underwriters Laboratories, and industries which are significantly at risk from lightning, such as telecommunications, wind generation, aviation, and fuel, have achieved consensus on the science of lightning protection and have embraced new protocols and practices. But the recreational boating industry has been slow to adapt those changes to the marine environment. There are at least three reasons for that.

There is no evidence from independent laboratories that these fuzzy lightning dissipators prevent strikes.

First, corrosion and motion on board boats, as well as limitations with respect to weight, space, and geometry, make lightning protection more challenging than in shoreside installations. Second, the mandate of the standards body for the industry, the American Boat & Yacht Council (ABYC), focuses on protecting life; protecting equipment has been a lower priority. Third, there has been strong disagreement between professionals about the best way to mitigate damage in a lightning strike and precious little data to support one point of view over another. The sometimes-raucous debate surrounding certain unproven lightning- protection devices and such theories as "fuzzy" lightning dissipation terminals and early-streamer emission terminals, as well as unorthodox placement of grounding terminals (a.k.a. grounding plates), have sharply divided the recreational boating technical community, all of which makes consensus on lightning protection difficult, if not impossible.

This lack of guidance is frustrating for those with boats at risk. While a runabout in Portland, Oregon, or a daysailer in Portland, Maine, may have little risk of lightning damage (see " Striking Lightning Facts "), larger vessels (particularly sailboats) in such lightning-prone areas as the Chesapeake Bay or Florida absolutely should be protected using the best technology available. Any marine-insurance adjuster can attest that the potential for loss on these vessels can be great. The National Fire Protection Association made some fundamental changes to the watercraft chapter of NFPA 780: Standard for the Installation of Lightning Protection Systems in 2008 that incorporate the thinking that has become accepted in other industries. While the recommendations in NFPA 780 have yet to be embraced by the recreational boating industry as a whole, understanding what it says — and why — may assist you in developing a lightning-protection plan for your boat.

Lightning 101

The simplest way to think of a lightning strike would be as a short circuit between the cloud and the earth. The earth and an active thundercloud have either a positive or a negative polarity with respect to each other, just like battery connections that can arc if they are not separated by a long enough air gap. Whether the positive charge is in the cloud or on the water may have great importance to a physicist, but matters little to the cow in the barn or the VHF radio antenna on the mast.

The important point is that the earth (or in our case, the water) contains an unlimited supply of positive and negative charges; it is the thundercloud that induces the charge concentration in the water. For example, if a large concentration of negative charge coalesces in a storm cloud over the ocean, a large concentration of positive charge is drawn to the very top surface of the water directly beneath it. (Opposites attract.) Since air is a good insulator, no electricity will flow between the cloud and the water unless the airborne charge loses altitude, moves close enough to the surface of the water, and the lightning jumps the gap. If an electrically conductive material, such as an aluminum tuna tower or mast, stainless steel rigging, or a long vertical copper wire, comes between the cloud and the water, then the gap that must be jumped becomes shorter. The boat short circuits the voltage, much like a wrench across battery terminals.

Because boats are built from electrically conductive components installed between the water and the areas aloft (masts, rigging, antennas, towers, support structures, electrical wiring), a lightning strike is inevitable if an active thundercloud containing electrical charges passes overhead at a low enough altitude. How much damage the lightning strike does to the boat depends upon how easily the electrical energy from the strike can find its way through the boat to ground. There will be a lot less damage if the discharge is contained in a well-designed lightning-protection system than if it takes a detour through the ship's wiring and sensitive electronics on its way out of the boat.

This is a basic concept that surprises many boaters: A lightning-protection system is not designed to prevent a lightning strike, but rather to provide a safe discharge path for the lightning. This is the only viable solution for lightning protection (short of going back to wooden ships, kerosene lamps, and sextants). The technology to prevent lightning strikes does not yet exist.

Still, there are devices out there claiming to do just that. Lightning dissipaters (LDs) look like metal bottle brushes or frayed paint brushes and are installed on the top of the mast. The hypothesis is that the numerous conductive points on the LDs safely dissipate accumulated charges so the lightning strike will not occur. As far as I am aware, not a single independent testing laboratory has confirmed the effectiveness of lightning dissipaters as lightning preventers.

Early-streamer emission (ESE) terminals have also gained traction in some circles. Fancy lightning rods often shaped like a torpedo that usually come with electronic circuitry, these are supposed to attract lightning better than a standard lightning rod (also called an air terminal), to ensure that the lightning strikes the grounding path rather than what is being protected. Once again, I am not aware of any independent studies validating the effectiveness of these devices.

Lightning-protection systems actually function by acting as the "best" short circuit between the cloud and the water, one designed to lead the lightning harmlessly to ground. The system accomplishes this in two ways: by attracting lightning away from more destructive pathways between cloud and ground, and by sending the charge around, instead of through, what it is protecting.

The first concept has traditionally been known as the "cone of protection" or the area protected by an air terminal from a strike. Traditionally, the cone of protection has been thought to include a circle centered on the base of the air terminal whose radius equals the height of the terminal and to extend from the top of the air terminal to the ground at a 45 degree angle. In fact, the length of the final jump that lightning takes before striking the air terminal is about 30 meters. Recent research suggests that the actual area protected can be defined by an imaginary sphere with this radius that is "rolled" up to the air terminal. All objects inside the imaginary sphere will not be protected by the air terminal, which means the area protected often differs in size and shape from the cone of protection model. Modern lightning protection for airports and power plants use the rolling sphere method and place air terminals so that the areas of protection overlap and include any sensitive equipment that would be damaged by a strike.

The second concept will be familiar to many as the Faraday cage. As early as 1836, Michael Faraday discovered that objects surrounded by metal were protected from lightning (explaining why we are safe from lightning while in our cars). Many old-school sailors have used Faraday's discovery to good purpose when they placed sensitive electronics in the oven during a lightning storm (with the oven off, of course.) This practice can be significantly updated by placing sensitive electronics in the microwave oven!

21st Century Lightning Protection

Benjamin Franklin pioneered lightning protection in 1749 with the invention of the lightning rod, and, when it comes to recreational boats, until recently, little has changed. Under his model, the lightning is attracted to the lightning rod (air terminal), which then passes the lightning current harmlessly to a submerged metaevent secondary flashes from these metal structures.

Air Terminals are shown in green; grounding plates with down, side flash, and equalization conductors in yellow; loop conductors in red; and catenary conductors in blue.

NFPA 780 draws much from the old-school system while incorporating improvements based on the modern understanding of lighting protection. While solutions will vary depending on the boat, let's talk about the basics.

Air terminals (lightning rod or Franklin rod) should be installed at the highest points of masts, towers, etc. On a sailboat a single air terminal could be bolted to the mast; on a sportfish it could be bolted to the tower and made to look like an antenna. This should be higher than anything you are trying to protect from a lightning strike, such as a VHF antenna.

A heavy electrical conductor should be connected from each air terminal directly down to a grounding point on the hull. In the case of a sailboat's mast, aluminum is a good conductor, so no separate wiring run needs to be installed. (Note that the wiring inside of the mast will be protected due to the Faraday effect.) An aluminum tower will work the same way on a sportfish so long as the legs are connected to an adequate grounding plate. Where no aluminum structure exists to act as a down conductor, a 4 AWG wire or larger should be run from the air terminal to the grounding plate in as straight a run as possible and well separated from other wiring.

The grounding point should be a corrosion-resistant metal plate installed on the exterior of the hull below the waterline. The plate should be at least one square foot in size and at least 3/16 of an inch thick. Research shows that most of the electrical discharge occurs along the edges, so a long, narrow plate, especially one with grooves cut in it, will be most effective at dispersing the charge. A new major point of contention is where to install the grounding plate, or plates. Some research indicates that a location at or near the waterline is by far the most effective solution. On a sailboat, the lead keel can be used as the grounding plate if the keel is not fiberglass-encapsulated or covered in fairing. If the mast is solidly keel stepped, there would be no need for a separate conductor from the mast to the keel. Metal rudders or propeller struts are also acceptable as grounding plates.

Protecting Electronics

Surge-protective devices (SPD) or transient voltage surge suppressors (TVSS) should be installed on all equipment that's mission critical, expensive, difficult to replace, and/or prone to lightning damage. Examples include the ECU/ECM, alarm systems, chartplotters, and instruments.

A bank of TVSSs protecting sensitive electronics.

TVSSs are the most exciting development in the field of lightning protection. These semiconductor devices provide protection by suppressing lightning-related voltage spikes. They are widely used in the telecommunications, wind generation, and avionics industries.

TVSSs are connected across the input terminals supplying voltage to a piece of equipment; they can be thought of as fuses that react to voltage instead of current. The TVSS is an open circuit as long as the supply voltage feeding the equipment is in the normal range. However, if a lightning strike causes a momentary voltage spike and puts, say 1,000 volts on a 120-volt device, the TVSS will "clamp" or short circuit 880 volts and convert it to heat. The excessive heat could, and probably would, damage the TVSS; but destroying a $250 surge arrestor to protect a $5,000 engine controller is good engineering.

Grounding plates should be long and narrow with groves cut into them to disperse the charge more efficiently.

Voltage surge protection would be prudent for engine controls, navigation systems, steering systems, and shorepower systems. TVSSs come in many voltage ratings, energy ratings, response times, and so on. Some are designed to protect whole distribution systems, while others are suitable for individual equipment protection only. A well-designed system includes cascaded protection, with extra protection on mission-critical and lightning-prone equipment, such as main engines and shorepower systems. The key to a reliable and cost-effective system is to ensure that appropriately rated devices are specified and properly installed. The best TVSS in the world will be ineffective if it is not connected properly.

Despite the best technology, there can still be challenges with an NFPA 780-based system, particularly when the system is improperly or only partially installed. For example, if the air terminal is installed lower than an adjacent antenna, it will not protect the antenna; in that case, the antenna cable carries the lightning current. Also, if the down conductor is connected to the bonding system rather than directly to a dedicated grounding terminal (ground plate), the lightning strike can energize the entire bonding system before discharging into the water. Another common mistake is to secure the lightning down conductor to other wiring. The high current from a strike through the down conductor can result in voltage surges in these adjacent wires, leading to additional damage in equipment that would otherwise be completely unaffected by the lightning strike.

In Conclusion

The recent revolution in marine electronics demands an evolution of our thinking on marine lightning-protection; equipment protection should be an important aspect of any modern lightning protection system. The knowledge and resources to safely transform this change in thinking into reality are readily available, both from the NFPA and industries also at risk from lightning. However, there are unique challenges on pleasure craft that are not addressed by others. These must be solved by sharing the experiences of lightning-protection systems and their effectiveness across the industry.

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James Coté

Contributor, BoatUS Magazine

James Coté is an electrical engineer, ABYC Master Technician, Fire Investigator and Marine Investigator. He operates a marine electric and corrosion control consulting firm located in Florida. For more information, go to: cotemarine.net

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How to Protect Your Boat From Lightning

Of all the dangers you can face at sea, lightning is one that almost no boater considers. Lightning is not a threat in the eyes of most people. It’s considered rare and unusual. You need to get that thought out of your head as a boat owner. Lightning strikes are far more common than you might think.

They key to staying safe from lightning at sea is preparation. You need to use a little help gleaned from 19th century scientist Michael Faraday. He can keep you safe from the total destruction of your electrical systems and a potential fire.

How Common Are Lightning Strikes on Boats?

According to the insurance provider BoatUS , the statistics are very unexpected. Around one in 1000 boats get hit by lightning every year. If there are about 12 million registered boats in America. Knowing that allows the numbers to become a little more clear. That’s 12,000 boats every year getting hit by lightning. One in 1,000 odds are not very high at all.

It should come as no surprise that taller boats are more at risk. This is for the same reason you see lightning rods on tall buildings. Lightning wants to get to the ground as fast as it can. It is attracted to conductive materials. The closer those materials are to the source of lightning, the more at risk they are. So anything tall and metal is at the greatest risk. The top of the mast on a sailboat is, in effect, a lightning rod at sea. If a sailboat and a jon boat are side by side on the water, the lightning will hit the sailboat every single time.

Likewise, the bigger the target, the more likely lightning is to hit it. Swap out the sailboat in our example with a yacht. The jon boat is still much safer. Bigger boats have more conductive materials on them. They have their own electrical equipment, which creates an electrical field. More metal parts will attract lightning. And simply having more area exposed makes it more attractive to a stray bolt from the sky.

It’s also worth noting that a multi-hulled boat is at greater risk as well. BoatUS stats show a multi-hulled boat is twice as likely to suffer lightning damage. On the upside, this doesn’t hold true for pontoon boats. In fact, they have statistically fewer instances of damage than other boats. So if you’re really worried about lightning, maybe give a pontoon boat a second glance.

• By the numbers, you want to have a bass boat, a pontoon boat , or a runabout. In 2012 and 13, insurance policy claims for lightning strikes on those boats were the lowest. They had a 0.1 chance in 1,000 of a direct lightning strike. That’s about as impressive as it can get.
• Averaged across all boats, the rate of lightning strikes was 0.9 in 1000. We’ve rounded that up to 1 in 1,000. Not trying to make things look worse than they are, but it’s just easier to say it that way. The point is mostly the same.
• A trawler or a motoryacht have a 1.5 in 1000 chance of being hit by lightning.
• A monohull sailboat will bump your odds of being struck significantly. At this point they are 3.8 out of 1000. More than double a trawler, nearly 4 times the average, and nearly 40 times what a bass boat is facing.
• A multihull sailboat has a 6.9 chance in 1,000 of being hit by lightning strikes. That’s about a 1 in 144 chance. You need a lighting protection system of some kind to avoid this. It won’t prevent lightning strikes, but it can prevent damage.

Why Are Multi-Hull Boats More at Risk?

Why is a multi-hull sailboat a danger when a pontoon boat is not? That’s a good question and there is not a good answer. As frustrating as that may be, not enough research has been done. So it’s not easy to explain why a multihull sailboat is so much more at risk than other boats. Since pontoon boats are actually below average, the reason is not immediately apparent. That doesn’t change the fact that statistics bear this out, however. If you have a multihull sailboat, it is at the greatest risk of lightning strikes. That means you’ll want to be a little more cautious than you otherwise would be.

How Does Boat Size Affect Lightning Strikes?

It’s not just the kind of boat you have that can attract lightning. As we said before, size is a factor. Smaller boats offer a smaller conductive path. They offer less chance for lightning to reach ground. Because of that, they are less likely to suffer a lightning strike.

If your boat is fifteen feet or less then you can rest a little easier. Statistically speaking, it’s not likely to be hit by lightning at all. It’s not impossible, but the numbers are not even charted, really. You have a 0 in 1,000 chance. That could mean you still have a 1 in 10,000 chance, so don’t think you’re fully immune.

At 16 feet to 25 feet your numbers increase. There’s a 0.2 in 1,000 chance of any boat at those sizes being struck.

There’s a significant increase above 26 feet. From there up to 39 feet your odds are 2.1 in 1,000. A boat of that size will have a lot more conductive material present. It’s also going to have more electronics on board and you need to worry about that. Lightning strikes and electronics do not mix at all.

Finally, a boat over 40 feet have a 6 in 1000 odds of being struck by lightning.

The mast of a sailboat is hands down the most attractive part of a boat for lightning. If your mast top goes from 35 feet to 45 feet, you just increased the odds of a strike threefold.

Where Is a Boat Most at Risk from Lightning?

Weather can be a very fickle thing. Depending on where you are in the country you may endure lightning storms all the time. Other spots almost never see electrical storms. So it stands to reason not every part of the country is as potentially dangerous as others.

The frequency of lightning flashes across the country follows a fairly reliable path. Nowhere is “safe” from lightning, but there are high concentrations and low concentrations. In fact, you can nearly bisect the country in a diagonal. The northwest United States suffers the least amount of lightning strikes. So up the Pacific Coast into Washington. This is where you will find the lowest frequency of lightning strikes.

You can draw an arrow from that point all the way down to the southeast tip of Florida. Southern Florida has the highest frequency of lightning strikes. Florida is the number one state for lightning damage to boats. Let’s take a look at the list for the top 7 claims locations.

• Mississippi
• South Carolina
• North Carolina

Only one state there isn’t down towards the south-east part of the state. Maryland comes in tied with Mississippi thanks to its high density of sailboats. Something to keep in mind. Even when something seems safe, it doesn’t necessarily mean that it is.

Claims for lightning damage along the Pacific Coast happen rarely. The frequency is around 1 in 10,000. Given how low that is, it should give you pause when you think of the Atlantic Coast. All of the numbers we’re presenting are averages. That means there are a lot of west coast boats that are never being struck. Therefore, there are more east coast boats getting struck by lightning to balance things out. Keep this in mind if you boat anywhere along the Atlantic.

The Pacific Ocean is colder. That means lightning occurs less frequently on that coast. The Atlantic Ocean is much more fertile ground for storms.

What Can a Lightning Strike Do to a Boat?

Now that you know the odds of a lightning strike, what next? How bad could a lightning strike be? Well, it can get pretty ugly. A mild lightning strike will render any fixed electronics useless. Radio , lighting, GPS , bilge pump , engines, you name it. Generators will likely be fried in most cases. It’s not unheard of for a DC solenoid to literally melt.

It’s possible your engine will still run after a lightning strike. But this is like a deer still running after it gets hit by a car. It can happen, but it’s not pretty. It also may not run for long. Expect frequent misfires if it’s still operational. Also, a lot of smoke. Your RPMs are going to drop significantly. Fire risk will greatly increase. The chances of it failing anytime thereafter are very high.

Other systems may continue to function but not in the intended way. We’ve heard of bow thrusters that will continue to run. The problem is you can’t turn them off and they may only run hard to port or starboard. Changing direction is no longer an option.

Suffice it to say lightning can utterly ruin your electronics. More than that, it can wreak havoc with your boat’s body. Most of the metal and writing in a boat is designed with a certain charge in mind. The average lightning bolt is 300,000 million volts and 30,000 amps. It has a negative charge and is DC current. Think of what kind of battery your boat runs on. Is it 12 volt? Maybe 24? No matter what it runs on, it’s not meant to handle lightning level power.

When lightning hits your boat, it’s going to follow the path of least resistance. Unfortunately, lightning can also make use of something called electromagnetic induction. That means if you have two wires near each other, the electrical charge can jump from one to another. Even if the second wire is not touching the first through which the current is flowing. Just being close enough to it allows the power to arc and continue on its path. Your boat is going to be small enough that the lightning is able to continue on a path. It will travel through wires and across metal fittings and fixtures.

Much of the wiring in your boat is likely to be melted completely by lightning. The power flow can actually blow a hole right through your hull. It’s also possible that it will burn the fiberglass around metal fittings. That can create holes and cracks and cause a boat to sink.

Boats on the water typically suffer less damage than those on trailers or stored out of water. On dry land, the electricity will follow a path down to whatever is holding the boat up. On some boats you can even see the scorched path and burn marks along the hull. In the water, the power dissipates more evenly. It will cause less destruction as it reaches ground. In this case, of course, ground is actually water. Lightning protection systems are therefore important in preventing this.

The Cost of Lightning Strikes

So what does all that damage do to a boat? More than 75% of all lightning strike claims are for less than 30% of the insured value. Of those damage claims, the vast majority of them are claiming electronics damage. That’s why, if you see a storm coming, it’s good to unplug those electronics that you can.

All of this being said, you need to keep things in perspective. You already know the odds on even getting hit by lightning in the first place. Suffering severe damage is still a rarity even when lightning strikes do occur. But the fact is it can happen, so you should be prepared. That’s where Michael Faraday and his Faraday Cage.

What is a Faraday Cage?

Michael Faraday created what is the basis for a modern lightning protection system. Lightning strikes can’t be prevented. They can be redirected, though. Faraday was convinced he could make a cage of conductive materials. The outside of the cage would redirect the electrical charge. This, in turn, would protect whatever was in the cage. You may have seen these before in YouTube videos.

The idea is to have this cage of conductive materials around a person or thing. All the metal is bonded together and carries the same electrical potential. Lightning follows the cage to the ground because it’s the path of least resistance. It’s like a bundle of lightning rods fused together. The electrical current can easily travel from the sky to the ground along it.

Obviously you’re not putting a literal cage around your boat to protect it from lightning. However, the same principles are used to protect your boat.

What’s the Best Lightning Protection System for a Boat?

In order to protect your boat from lightning strikes you need a way to redirect those strikes. Your cage is not a literal one but it does require certain conductive materials. You’ll need a marine electrician’s help here. They can put together the best protection system for your particular vessel.

In general, it works like this. Heavy conductors are used to create a cage by bonding all of your boat’s metal components. This starts at the top of the mast and must include all of the major components we have mentioned. Outriggers, railings, arches make a good framework. The AC compressor, engines, stove and other electronics need to be included as well.

A low resistance wire can connect all of these components and offer a path for the lightning to travel. The current will travel to ground, or in this case water, along the path. It can exit the boat through the propeller shaft or keel bolts. Ideally, though, you want a separate system in place. At least one square foot in diameter external ground plate is ideal. The electrical current can be routed to the ground plate and avoid damage to the rest of the boat.

Your engines should be bonded. This helps you avoid something called side flashes.

What is Thompson’s Lightning Protection System?

The National Fire Protection Association helped devise a system. Along with the American Boat and Yacht Council, they created this method. It was devised by Electrical engineer Ewan Thompson. He developed it as the best way to protect a boat from lightning.

• Start with lightning rods. A single rod protects in a cone of about 45-degrees. You want more than that, of course. Several lightning rods set up around a boat provide maximum lightning protection. Thompson found that the best lightning rod is a ½ inch in diameter with a rounded top. Located at the bow, the stern, and above the highest points can help create the basis of your cage.
• The rods need to be connected with heavy two-gauge wire. The wire needs to travel the easiest path to the water’s surface. If there are bends, they need to be long, sweeping ones. Remember, the current could potentially leap from one wire to another. This will happen if they are too close together. Run them outboard and keep them two feet away from any other wires. This is especially important if they are on parallel paths. Any closer and you risk electromagnetic induction. Then all your hard work will be for nothing.

If there is a point where your lighting wires cross normal wires, make it a right angle. Induction has the least chance of happening at right angles. It keeps the contact to the bare minimum.

• Rails and aluminum supports for a hardtop can become part of the cage. Bridge any gaps with wire, however. If the wire doesn’t connect gaps in rails, it can’t work.
• Create your Faraday Cage. You have the top of your cone of protection set up now. But to make it a cage you need one continuous band around the entire boat. This can be either one wire or a metal strap. It should be located below the level of the deck but above the waterline. Some manufacturers of boats include these bands right in the hull. Just above the waterline you’ll find a copper band around the entire boat. All the wires can be connected to it to dissipate any lightning strikes.
• Thompson’s method also includes the use of sparking electrodes. These small devices can be affixed around the boat above the waterline. They’re made from stainless steel or graphite and other fire-resistant materials. They allow the current to discharge into the water. When lightning does strike, it will typically blow them out so they will need to be replaced. It’s recommended they be placed most frequently near the bow. That’s where the majority of lightning strikes seem to occur.
• To avoid that side flash on your engine, you need to run more two gauge wire. Connect it to where the bonding system connects the engine. From there it can go to the electrodes. Also it can be connected to submerged grounding strips above and outboard of the prop. This is a better solution than letting the propeller take the electrical charge. You can also connect bow thrusters in this manner. When this is done properly, your thrusters and engines are all part of the cage as well.

Finally, use surge protectors. These are especially useful for your GPS and VHF radio . They can suppress voltage above 300 volts. As we’ve seen, that would be pretty important in a lightning strike. The result is knowing your expensive electronics can be protected.

How to Handle a Lightning Storm on a Boat

So, let’s say you have your boat all set up now. There’s a Faraday Cage, and you have your cone of protection. There’s a storm brewing and you can see lightning in the distance. Are you safe to wait it out? Maybe. But don’t risk it.

If you ever have the option, leave. Outrun a lightning storm whenever it is feasible to do so. Running for protection is always better than facing lightning in the open water. If that is not an option, then do your best to prepare. Make sure you pull in any fishing lines and bring in any swimmers if possible. Lightning can actually strike up to one mile ahead of a storm.

Turn off any electronics that you don’t need and stay low and centered in your boat.

What to Do If You Think Your Boat Was Hit?

Many lightning strikes are going to happen when you’re not there. Your boat will be in the marine while you’re at home. You’ll get to the boat and realize things aren’t working. The fridge is off, the radio is a no go, nothing that runs on power is turning on.

You have a few steps you should follow. These will allow you to give your vessel a thorough check after a suspected lighting strike.

• Turn off all of your battery switches
• Unplug shore power to prevent the possibility of a short circuit
• Check your bilge . If the bilge isn’t dry you may have an issue below the waterline and you’ll want to have the boat hauled out.
• You’ll need to call your insurance company once your boat is secure. If you know it’s not taking on water a haul out may not be necessary.
• Keep any damaged electronics or parts. The insurance company will want to assess them before they get tossed out.
• A marine surveyor can come and assess your boat. They’ll be able to determine what works and what has been destroyed. If the insurance company deems it necessary, they may pay for a haul out as well. That way everything below the waterline can be inspected.

The Bottom Line

Lightning damage is definitely a rare thing. But on the water it’s a lot more common than most boaters realize. It’s not the sort of thing you need to lose sleep over, but you should be prepared. Lightning protection systems are invaluable. You don’t want to be on the wrong end of a lightning strike one day. The saying “better safe than sorry” definitely applies here. If you have a sailboat, consider protection. Likewise if it’s a large boat, or one on the Atlantic coast anywhere. An ounce of prevention is worth a pound of cure.

My grandfather first took me fishing when I was too young to actually hold up a rod on my own. As an avid camper, hiker, and nature enthusiast I'm always looking for a new adventure.

Categories : Boats , nauticalknowhow

Paul on August 4, 2021

…”lightning hits your boat, it’s going to follow the path of least resistance. Unfortunately, lightning can also make use of something called electromagnetic induction. That means if you have two wires near each other, the electrical charge can jump from one to another. Even if the second wire is not touching the first through which the current is flowing. Just being close enough to it allows the power to arc and continue on its path.”…

The article is very informative but misses out some stuff & is possibly misleading in parts.

Arcing between wires is not electromagnetic induction. Electromagnetic induction is due to the fact that a lightning strike consists of repeated sharp rises & falls in large currents which produces an RF effect which creates rapidly changing magnetic fields which results in induced voltages in cables intersected by the changing magnetic fields.

One of the basic methods of protecting electrical & electronic equipment is to have twisted pair cables, mu metal cable shielding, arranging for most cable runs to be as horizontal as possible with all vertical runs in one place In heavy magnetic shielding conduits and ensuring that lightning current is always as vertical as possible. All mast cables should be connected by easy to reach & disconnect plug & sockets that can quickly be unplugged if needed.

Ben on August 23, 2021

What about galvanic considerations?

Chuck Dickey on September 2, 2021

So should you unplug shore power before a lightning storm?

Jeffrey M Streib on February 13, 2023

What effect might a lightning strike have on:

-The batteries and their capacity -Speakers

I suffered a lightning strike and lost almost all electronic components, engine components, gps, vhf steer by wire etc.

The insurance company has been good overall, but the surveyor doesn’t think the (3) batteries speakers, and bilges were related to the strike. (They all worked fine prior)

Any help would be appreciated.

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• Digital Edition

Yacht lightning strikes: Why they cause so much damage and how to protect against them

• August 27, 2020

A lightning strike may sound vanishingly unlikely, but their incidence is increasing, and a hit can cause severe damage costing thousands of pounds, as well as putting an end to a sailing season, writes Suzy Carmody

Lightning strikes of boats are still fairly rare – but are on the increase. Photo: Image Reality / Alamy

Pantaenius handles more than 200 cases of lightning damage every year. “Over the past 15 years, the total number of such loss events has tripled in our statistics. The relative share of lightning damage in the total amount of losses recorded by us each year is already 10% or more in some cruising areas such as the Med, parts of the Pacific or the Caribbean,” added Pantaenius’s Jonas Ball.

Both UK and US-based insurers also report that multihulls are two to three times more likely to be struck by lightning than monohulls, due to the increased surface area and the lack of a keel causing difficulties with adequate grounding. Besides increased likelihood of being hit, the cost of a strike has also risen enormously as yachts carry more networked electronic devices and systems.

The CAPE index measures atmospheric instability and can be overlaid on windy.com forecasts

Avoiding lightning strikes

The only really preventative measure to avoid lightning is to stay away from lightning prone areas. Global maps of lightning flash rates based on data provided by NASA are useful to indicate areas of more intense lightning activity. They show that lightning is much more common in the tropics and highlight hotspots such as Florida, Cuba and Colombia in the Caribbean, tropical West Africa, and Malaysia and Singapore in south-east Asia.

Unfortunately, many of the most popular cruising grounds are located in tropical waters. Carefully monitoring the weather and being flexible to changing plans is an essential part of daily passage planning during the lightning season in high-risk areas. CAPE (Convective Available Potential Energy) is a useful tool for indicating atmospheric instability: you can check the CAPE index on windy.com (see above) as part of your lightning protection plan.

Protection against lightning strikes

Yachts that had no protection when lightning struck often experience extensive damage. The skipper of S/V Sassafras , a 1964 carvel schooner, reports: “Most of the electronics were toast. Any shielded wiring or items capable of capacitance took the most damage: isolation transformer; SSB tuner; autopilot and N2K network Cat 5 cables.”

Article continues below…

What is a Spanish Plume? Thunderstorms, lightning and downdrafts explained

Earlier this summer we saw considerable thunderstorm activity over the UK and Europe, resulting in flooding and some serious injuries.…

Expert sailing advice: How to handle a lightning strike on board

Lightning is the thing that scares me the most at sea. Having never experienced a lightning strike I think this…

The owner of Matador of Hamble , a Rival 41, recalls the effects of their strike: “The extent of the damage was not immediately obvious. For days afterwards anything with a semi-conductor went bang when we turned it on.”

The crew of Madeleine , a Catana 42S catamaran, had a similar experience. “We were struck in Tobago but only discovered the electrical damage to the port engine when we reached St Lucia and it was in the Azores that we found out the rudder post was broken and we had lost half our rudder.”

It therefore seems prudent that in lightning prone areas a protection system should be implemented where possible to protect the boat, equipment and crew. As a first step analysing the boat and the relative position of all the main metallic fittings can often reveal a few safe places to hide and places to avoid. Areas such as the base of the mast, below the steering pedestal and near the engine have the highest risk of injury.

Stays on a steel boat are attached directly to the steel hull. Photo: Wietze van der Laan / Janneke Kuysters

In terms of minimising the effect of a strike, one temporary method to limit the damage is to direct the current outside the boat using heavy electrical cables attached to the stainless steel rigging. With the other end of the cable immersed in the ocean, this provides a conductive path from the masthead to the ground.

The main flaw in this plan is that an aluminium mast has much greater electrical conductivity than stainless steel and is a more likely pathway to the ground. This system also requires adequate copper to be in contact with the seawater to discharge the current.

Other temporary measures include disconnecting radar and radio aerial cables, putting portable electronic items in the oven or microwave as a Faraday cage, turning off all the batteries or nonessential electronic equipment if at sea, or in a marina unplugging the shore power cord. All these procedures rely on someone being on board with several minutes warning before a strike to drop the cables over the side and turn off/disconnect and unplug.

Cable used as a down conductor from the shrouds on a catamaran. Photo: Wietze van der Laan / Janneke Kuysters

Posting an ‘Emergency Lightning Procedures’ card in a central location of the boat showing where to stand and what quick preparations to take is a simple first step.

Permanent lightning strike protection

In a thunderstorm, molecular movement causes a massive build up of potential energy. Once the voltage difference overcomes the resistance of the airspace in between, invisible ‘channels’ form between the base of the clouds and tall objects like masts, providing a path for a lightning strike to discharge some of the accumulated electrical energy. There will be less damage to a vessel if the discharge is contained in a well-designed lightning-protection system.

Lightning rods or air terminals installed at the top of the mast connected to an external grounding plate on the hull, via an aluminium mast, provide a permanent low impedance path for the current to enter the water. On boats with timber or carbon masts a heavy electrical cable can be used as a down conductor.

If not installed during production, a grounding plate can be retrofitted during a haul out. On monohulls a single plate near the base of the mast is adequate. A ketch, yawl or schooner requires a vertical path for each mast and a long strip under the hull between the masts, whereas catamarans usually require two grounding plates to complete the path to the water.

The current from a lightning strike is dissipated primarily from the edges of the plate, so the longer the outline the better. Warwick Tompkins installed a lightning protection system designed by Malcolm Morgan Marine in California on his Wylie 38 Flashgirl :  “Two heavy copper cables run from the foot of the mast to the aluminium mast step, which was connected to a copper grounding plate on the outside of the hull via ½in diameter bronze bolts.”

The grounding plate was an eight pointed star shape. “Some liken it to a spider.” Warwick says, “And the very minimal electrical damage we experienced when struck was directly attributable to this spider setup.”

A copper ‘X’ grounding plate, used on boats that have a fin keel some distance aft of the mast. Photo: Malcolm Morgan Marine

Morgan adds: “Any cables associated with lightning protection should be routed away from other ship’s wiring wherever possible. For example, if the navstation electronics and main switchboards are on one side of the vessel, the lightning protection cables should be routed on the opposite side.”

An internal bonding circuit connects the major metal objects on a boat to the grounding plate via bonding cables. This can help prevent internal side strikes where the current jumps between objects in order to reach ground.

Morgan explains: “As modern boats are becoming increasingly complex careful consideration is required to ensure the bonding system is designed correctly. There are five possible grounding systems on a vessel (lightning protection, SSB radio ground plate, bonding for corrosion, AC safety ground, and DC negative) and all need to be joined at one common point and connected to the external grounding plate.”

This strike exited through the keel, blowing off the fairing and bottom paint. Photo: GEICO / BoatUS Marine Insurance

Surge protection

Yachts anchored close to shore or on shore power in a marina are susceptible to voltage surges during a thunderstorm. If lightning strikes a utility pole the current travels down the electricity cable looking for ground. It can enter a vessel through the shore power line or can pass through the water and flashover to a yacht at anchor.

Surge-protective devices (SPD) are self-sacrificial devices that ‘shunt’ the voltage to ground. They reduce the voltage spikes eg a 20,000V surge can be diminished to 6,000V but the additional current can still be enough to damage sensitive electronics. Therefore fitting ‘cascaded’ surge protection with several SPDs in line on critical equipment is a good idea.

High-tech solutions

Theoretically, if a lightning dissipator bleeds off an electrical charge on the rigging at the same rate as it builds up it can reduce or prevent a lightning strike. Lightning dissipators such as ‘bottle brushes’ are occasionally seen on cruising boats, though these are relatively old technology. Modern dissipators feature a 3⁄8in radius ball tip at the end of a tapered section of a copper or aluminium rod. The jury is out on their effectiveness.

A more high-tech solution is Sertec’s CMCE system, which claims to reduce the probability of a lightning strike by 99% within the protected area. The system has been widely installed on airports, stadiums, hospitals and similar, but has now been adapted for small marine use (and may reduce your insurance excess).

Arne Gründel of Sertec explains: “The CMCE system prevents a lightning strike by attracting and grounding excess negative charges from the atmosphere within the cover radius of the device. This prevents the formation of ‘streamers’, and without streamers there is no lightning strike.”

A Sertec CMCE marine unit, designed to dissipate lightning

• 1. Avoiding lightning strikes
• 2. ‘A lightning strike caused £95,000 of damage to my yacht’

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Getting the Charge Out of Lightning

No matter how well protected the boat may be, few manage to escape unscathed..

Miraculously, relatively few people are injured in lightning strikes. Frequently, of course, no one is aboard the boat when it is struck, and it is only by after-the-fact detective work that the extent of damage is discovered.

There are, however, two attendant bits of unpleasantness water, and contaminates like dirt, dust, rust, scale, bugs, and bones.

Most boat owners have only the vaguest idea of what is involved in protecting their boats from lightning damage. Many believe that their boats are already protected by the boat’s grounding system. Most are wrong.

Just because your boat may be bonded with heavy cop-per conductors connecting the masses of metal in the boat doesn’t mean that it is protected against lightning. A bon-ding system may be a part of a lightning protection system, but bonding itself offers no protection to the boat unless a good, direct path to ground is part of the system.

The purpose of bonding is to tie underwater metal masses in the boat together to reduce the possibility of galvanic corrosion caused by dissimilar metals immersed in an electrolyte. The purpose of lightning grounding is to get the massive electrical charge of a lightning strikethrough the boat to ground with the least possible amount of resistance.

Most lightning never reaches the earth: it is dispersed between clouds of different electrical potential. The lightning that concerns sailors is the discharge of electricity between a cloud and the surface of the earth, or an object on the surface of the earth, namely, your boat. The amount of electricity involved in lightning can be, well, astronomical. We’re talking about millions of volts.

Granted, the duration of a lightning strike is extremely short. But in the fraction of a second it takes for lightning to pass through your boat to ground, a great deal of damage can be done. And here’s the kicker. No matter how elaborate your lightning protection system, there is no guarantee that a lightning strike will not damage your boat.

Certainly you can reduce the potential damage from a lightning strike. That’s what protection is all about. But to think you can eliminate the possibility of damage is folly. There are too many recorded instances of so-called properly lightning-protected boats suffering damage to believe in the infallibility of lightning protection systems.

The goal of lightning protection is to offer a low resistance path to ground, in this case, the water. On a sailboat equipped with an aluminum mast and stainless steel standing rigging, the basic components of the lightning protection system are in place.

While neither aluminum nor stainless steel is an outstanding electrical conductor, the large cross-sectional area of both the mast and the rigging provide adequate conductivity for lightning protection. The trick, however, is get-ting the electricity from the mast and rigging to the water.

The straighter the path is from conductor (mast and rigging) to ground, the less likely are potentially dangerous side flashes. Put simply, side flashes are miniature lightning bolts which leap from the surface of the conductor to adjacent metal masses due to the difference in electrical potential between the charged conductor and the near by mass of metal. Ideally, therefore, the path from the bottom of the mast and rigging to ground would be absolutely vertical. In practice, this is rarely achieved.

If the boat has an external metal keel, the mast and standing rigging is frequently grounded to a keelbolt. There are pitfalls to this method. First, the connection between the bottom of the mast and rigging to the keelbolt must be highly conductive. ABYC (American Boat and Yacht Council) standards say that each primary conductor for lightning protection systems should have a resistance equal to or less than a #4 AWG copper conductor. (Secondary conductors should have resistance not greater than a #6 AWG copper conductor.)There is no drawback to using an even larger conductor.

Connecting the short conductor to the mast and keelbolt presents some problems. A crimp eye can be used on the end that is to be attached to the mast, but you may have to fabricate a larger eye for attachment to the keelbolt. This can be made from sheet copper. Soldering the connections is not recommended, since the heat generated in a lightning strike could melt the solder.

Then you have to face up to a basic problem. Your mast is aluminum, yet you’re connecting it to ground with a copper cable. Everyone knows that aluminum and copper are not galvanically compatible, so what’s the solution? While it will not eliminate corrosion, a stainless steel washer placed between the copper cable’s end fitting and the aluminum mast will at least retard it. But this connection is going to require yearly examination to make sure that a hole isn’t being eaten through the mast. In addition, of course, the process of corrosion creates wonderful aluminum oxide byproducts, which have very low conductivity. The aluminum oxide may reduce conductivity to the point where your theoretical attachment to ground is in fact non-existent. Once again, disassembling the connection and cleaning it yearly are essential to maintain conductivity. Constant attention to all the conductor connections is essential in any grounding system, whether it’s for lightning protection or grounding of the electrical system.

Even if all the connections in the system are flawless, you’re faced with getting the electrical charge out of the boat and into the water. Keels are always coated with bottom paint. Depending on the type of bottom paint used, the keel itself may be a fairly poor ground. An iron keel properly primed with epoxy mastic before bottom paint is applied is fairly well isolated from the water. If it weren’t, it would rust. The same goes for lead keels prepared in the same way. In practice, the electrical charge will probably be powerful enough to get to ground through the protection system on the keel. The same problem exists, of course, on painted metal boats with their systems of barrier coats. The barrier coats reduce conductivity, but do not eliminate it.

Do not under any circumstances ground the rigging or mast to ballast located inside a fiberglass hull shell. The electrical charge tends to travel on the surface of the conductor. Finding no path to ground from the isolated inside ballast, you may literally blow a line of holes through the hull along the top of the ballast line. Surveyors have reported occurrences of this type of damage to us, as strange as it may sound.

For boats with inside ballasting, or for powerboats, some type of external grounding plate is required. These are usually made from sintered bronze: tiny particles of bronze fused into a porous block. The effect is to give a much larger surface area than defined by the dimensions of the block itself. It is very important to use as large aground plate as necessary, and to position it as close to vertically in line with the primary lightning conductor (the mast) as possible.

Racing boats are not going to be willing to do this, since a ground plate creates a fair amount of drag in light air. Cruisers would be advised to trade off the drag for the protection offered.

A grounding plate installation is not a nail-it-in-place-and-forget-it installation. As with any bare metal underwater, oxides build up in the grounding plate, reducing its efficiency. The manufacturer of the plate can tell you the proper remedies, which may include removing the plate yearly and treating it in an acid bath to restore proper conductivity.

It is probably a poor practice to use the same grounding plate for lightning grounding and grounding of electronics such as Loran. If the lightning charge is too great for the plate to instantaneously transmit to ground, the charge may travel back through the ground wire to your electronics, with disastrous results.

For this article in its entirety please click the below link…

Getting the Charge Out of Lightning   

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An approach to a modern sailboat lightning protection system

We were lucky when we were struck by lightning on our small 35’ GRP cruising sailing boat in Turkey in 2013, but without an LPS. All the plastic and some of the metal gear at the top of the mast exploded (see photo below) and simultaneously the headlining in the saloon exploded downwards with a loud bang. So much smoke that we initially thought we were on fire; but my wife and I survived unscathed to tell the tale.

The most likely discharge exit was through the propeller shaft, but practically all electronics were violently destroyed and, as an electrical and electronic engineer, my assessment for our insurance claim afterwards showed that most devices had experienced severe arcing with small electronic components having exploded internally (see photo below).

An lightning protection system is a bonding, grounding and shielding arrangement made of four distinct parts: Air terminals, down conductors, a low-impedance ground system and sideflash protection.

The best lightning protection system cannot guarantee personal protection, or protection from damage to sensitive electronic equipment. Also it is not a lightning prevention system. I knew the private owner of one large blue water catamaran which has been struck three times in its life and it is not an old boat. Fortunately no one was hurt on any occasion, but many electronic systems on that complex boat were effected and had to be replaced on each occasion. Unfortunately catamarans are many times more likely to be struck than mono-hulls and records in the USA, where certain locations are particularly prone to electrical storms (e.g. Florida where boat ownership is high), show that mono-hull sailing boats are about 25 times more likely to be struck than motoryachts.

Lightning is very hard to study and to accurately predict its behaviour is almost impossible, but it is driven by the simple fact that a massive potential difference (voltage) exists between the highly charged clouds of a brewing thunderstorm and the surface of the Mother Earth. Eventually, a path is found through the atmosphere down to ground for some of the accumulated charge to discharge and the creation of a discharge path first requires the creation of so called ‘streamers’ [1],[2]. Bear in mind that air breaks down at 3 million Volts per metre, and you get some inkling of the enormous voltage differences involved.

In the middle of a large body of water, with your sailing yacht in it, the top of the mast, being the highest point around, looks like a handy point to discharge through. So the LPS is designed to control the first point of discharge and then make the onward path to ‘ground’ – in this case the sea – as direct as possible and capable of conducting very high currents for a very short time during the discharge.

In 2006, the American Boat and Yacht Council (ABYC) technical information report TE-4 [3], [4] recommended the following:-

• lightning protection system conductors must be straight and direct and capable of handling high currents. The main ‘down’ conductor is recommended to be 4AWG, or 25mm2 in European sizing; see diagram.

• A large enough area ground must be provided between the vessel and the water to offer an adequately low resistance path (ABYC recommends 1sq.ft. {0.1m2} in salt water; much larger in fresh water. NB this is not adequate for acting as the SSB counterpoise). Metal-hulled vessels naturally offer a large ground contact area with the sea, but the connection between the hull and all other electrical systems needs careful consideration.

• Heavy metal objects such as fuel tanks and engines must be bonded to the ground bonding arrangement to reduce the risk of ‘side flashing’ where the lightning literally can jump from one conductor to another, seemingly better path. Similarly, it can jump out of corners in cabling, so if bends must be made, then they should not be more than 90° and with as large a bend radius as possible.

The basic arrangement is as depicted in the diagram, where the ‘air terminal’ is a rounded end (circled in photo) metal wand mounted at the top of the mast to ‘attract’ lightning to it and, most importantly, to stand at least 6” (15cm) higher than anything else e.g. above the VHF or other antenna. Providing the air terminal is securely electrically bonded, presenting a high surface contact area, low resistance path to an aluminium mast, the mast itself can be used as the down conductor at least to the deck or keel, depending on where the mast is stepped. In the case of wooden, or carbon composite masts they present too high electrical resistance and a 4AWG cable must be run straight down the mast as the main down conductor. From the bottom of the aluminium mast or down conductor, the 4AWG onward path needs to be as direct and short as possible to the ground plate, or the metal hull.

It is actually better to leave through-hull metal fittings electrically isolated if they are already insulated from the rest of the boat by dint of their attached rubber or plastic hoses and their insulating mounting plates – decent quality bronze alloy seacocks and engine intake strainers will not unduly corrode if left submerged for extended periods of time without needing connecting to the vessel’s earth bonding. However, in the US it is more normal to bond everything metal below the waterline, use a tinned copper bus bar running the necessary length of the vessel, above any bilge water level, to connect each through-hull fitting to, which is then connected at one point only to the main grounding route out of the boat. This bonding arrangement is gaining in popularity outside the US with consideration of a lightning protection system.

Note in the diagram that all tie-ins, including fore- and back-stay (unless insulated) must use at least 6AWG (16mm2 European) cable. All large metal objects within 6ft (2m) of the lightning down path also need tying in with 6AWG (16mm2) cable. Examples are metal fuel tanks, main engines (despite them usually already being connected to the water via their prop shaft) and generators; this is to minimize the risk of ‘side flashing’ where lighting can literally jump from conductor to metal object, looking for a better path to ground, even if one does not exist.

In considering of the creation of a ground plate of sufficient size, a metal hulled vessel is ideal, but nevertheless only one electrical connection point to the hull should be made from the main 4AWG down conductor. This same point should have all the other earth bonding made to it alone. The DC main negative bus in turn should be connected to the earth bonding in only one place, though European boats generally have their DC system isolated from any bonding system to discourage DC earth faults, the US differs in this respect, preferring direct bonding. One solution to this dilemma is to use a suitably rated surge capacitor between the DC negative busbars and the bonding system for the LPS. In the case of a non-metal hulled sailing vessel, the attraction of using the keel as a discharge point should be resisted as it is in contact with the water some distance below the surface where already a lot is going on with respect to charge balancing, so an alternative point is likely to be sought out by the discharge, nearer the surface. It seemed clear to our very experienced (and ancient) marine insurance surveyor that, during our own strike in Turkey, the discharge was out through the propeller shaft.

So far, so good, but recent thinking and good practice [5],[6] has modified the above ideas to take into consideration the danger of side flashing much more. A side flash is an uncontrolled spark that carries current to the water and can do extensive damage to hulls and equipment. The good practice and standards for a lightning protection system relating to marine situations, such as they exist (see NFPA 780, latest version, especially chapter 8, ‘Protection for Watercraft’, [7]) are tending to treat a boat more and more like a building to exploit those well tried and tested techniques used in a land based situation. Rather than a ‘cone’ below the air terminal, the ‘zone of protection’ is now more reliably envisaged to be formed from a ‘rolling sphere’ of 30m radius, as shown below for a larger yacht [7],[8]:-

Diagram of Boat with Masts in Excess of 15 m (50 ft) Above the Water; Protection Based on Lightning Strike Distance of 30 m (100 ft).

With a large building, the down conductors from the various air terminals run down the outside of the building to a number of grounding stakes; not so with a yacht where, as we have described, we’ve now concentrated the discharge right in the middle of the boat, where the danger of side flashing into other metal parts is very real; if these parts are not bonded and protected by a properly designed, low impedance path there’s are very real further danger of the side flash finding its way onwards and out through the side of the boat to the surrounding water surface. This has indeed been experienced by an American friend of mine on a high-tech, all carbon racing sailing boat on its way back to Newport, which after being unavoidably struck several times in a violent storm, put in to New York and immediately hauled to find literally a thousand or more tiny holes around the waterline when the discharge had exited! Apparently lightning does not always take the straightest path to the water, but rather has an affinity for the waterline.

The latest version of this NFPA 780 standard recognises this danger and, in a departure from the older versions, provides for multiple grounding terminals to provide the shortest path to the surrounding water surface. These ‘supplemental grounding electrodes’ conduct lightning current into the water in addition to that conducted by a main ground plate. The new standard provides for a continuous conducting loop outboard of crewed areas, wiring and electronics. Placing the loop conductor well above the waterline, outboard, and with grounding terminals below it retains the advantages of an equalization bus, whilst correcting for its weakness with side flashes having nowhere else otherwise to go.

Protection of electronic equipment by a hermetic system on larger yachts

So much electronic equipment on board a yacht struck by lightning is very susceptible to permanent damage. The only safe way to fully protect electronic equipment is to have it completely disconnected from all other circuits when thunder and lightning are nearby, and I still to this day do that as much as possible, but how practical is complete protection really?

A recent idea I had whilst discussing the problem with a 30m ketch owner may have some merit, and I call it a ‘hermetic system’, so suggesting that it is sealed from the outside world: If the most critical and/or sensitive electronic equipment can be enclosed within its own quite separate power and cabling set, separate from the rest of the boat’s electrical and electronic wiring, then it is possible that it could be saved in the event of a lightning strike. One way to do this would be to run all those systems required to be protected effectively off an Uninterruptable Power Supply (UPS), powered from the AC bus (via the generator), then down converted to the necessary 24/12VDC electronics supply. In the event of a lightning storm, all AC connections to the UPS and any signals, power or ground returns outside the hermetic system must be open circuited by large clearance contactors. The electronics contained within the hermetic system can still continue to operate, for a limited time (depending on the capacity of the UPS batteries) and further choices can be made about what to shut down within the hermetic system to extend the battery life, leaving for example just the absolute minimum electronics to continue to safely navigate e.g. Depth, GPS, Chartplotter. Very careful consideration must be given to cable runs.

The VHF antenna on the main mast may be protected by a surge arrestor from one of several suppliers e.g. www.nexteklightning.com. No guarantee is likely to the effectiveness of this as a protection device in all cases of lightning strike and the manufacturers should be consulted for further information.

I certainly now resort to the marvel of a GPS chart plotter on my mobile phone when there’s a nasty electrical storm about and I’m out at sea! References: –

1. Top 10 best lightning strikes (USA) by Pecos Hank, with rare photo of an upward streamer. 2. http://marinelightning.com/index_files/SFMechanism.gif for a graphic showing the formation of negative streamers 3. ABYC (US) technical report TP-4 “Lightning Protection”. 4. Nigel Calder – “Boatowner’s Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat’s Essential Systems” 5. “Complexities of Marine Lightning Protection”, By Ron Brewer, EMC/ESD Consultant, April 2011 6. “A New Concept for Lightning Protection of Boats – Protect a Boat like a Building” Ewen M. Thomson, Ph.D.; published in the October 2007 edition of Exchange 7. National Fire Protection Association (US) document NFPA 780-2014 “Standard for the Installation of Lightning Protection Systems” – see especially chapter 8 ‘Protection for Water craft’. 8. “Evaluation of Rolling Sphere Method Using Leader Potential Concept – A Case Study” P.Y. Okyere, Ph.D & *George Eduful – Proceedings of The 2006 IJME – INTERTECH Conference

Feature article written by Andy Ridyard. Andy Ridyard has been a professional electrical and electronics engineer for more than 35 years and started SeaSystems in 2008. His business is dedicated to providing troubleshooting, repair and installation services to superyachts internationally, specialising in controls and instrumentation. He lives with his wife in Falmouth, UK, but works mostly in the Mediterranean. SeaSystems has fixed countless intractable problems with marine control systems, marine electronics, Programmable Logic Controllers (PLCs) and marine electrical systems. For more information visit SeaSystems.biz .

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What to do in a Lightning Storm on a Boat

• By Mike Telleria
• Updated: February 10, 2020

Powerful, dangerous, highly unpredictable — all are common descriptions of lightning storms. A direct strike that results only in ringing ears and a few roasted electronics would be considered lucky. Unlucky would be through-hulls blown out, a sunk boat or worse — possibly serious injury or death.

Many powerboaters like to think that they’ve got the speed to simply outrun or get out of the way of lightning storms , or they figure they’re safe if they go boating only when it’s clear and sunny. That’s an attitude aided by the low odds of a boat being struck by lightning, which BoatU.S. pegs at about one out of 1,000 boats in any given year.

No worries, right, mate? Wrong.

Engines can malfunction ; big lightning storms can leave no room to escape; sunny mornings can turn into dark, threatening afternoons. If yours is the only boat in the area during a lightning storm, the odds of being struck go way up, leaving you and your crew vulnerable to millions of volts raining down from the skies. Lightning and boats do not mix. While manufacturers can build in a degree of protection, lightning protection begins with boaters being informed and prepared to act in the event of a thunderstorm or actual strike. You should know the following techniques and strategies.

Boating in a Thunderstorm is Bound to Happen at Some Point

A strategy of boating only on sunny, cloudless days may work well in places like Idaho and California, but that would mean almost never using the boat in places such as Florida, Louisiana and much of the Midwest. For example, most of Florida — the Sunshine State — has at least 70 to 80 thunderstorm days per year, with some parts having more than 100 thunderstorm days per year (with increased activity during the summer months).

Absolutely, boaters should track VHF , Internet and television weather reports and make responsible decisions about whether to go boating depending on the likelihood of lightning storms. Short-term forecasts can actually be fairly good at predicting bigger storms, but small, localized storms might not be reported. This is when knowing how to read the weather yourself can come in handy. (The U.S. Power Squadrons offers great weather courses for boaters, and there are many books that cover the basics.)

Lightning strikes typically occur in the afternoon. (Florida estimates 70 percent occur between noon and 6 p.m.) A towering buildup of puffy, cotton-white clouds that rise to the customary flat “anvil” top is a good indication to clear the water and seek shelter — or move out of the storm’s path if possible. That’s if the storm is at least somewhat off in the distance (most storms are about 15 miles in diameter and can build to dangerous levels in fewer than 30 minutes). If lightning and thunder are present, just count the seconds between the lightning and corresponding thunder and then divide by 5 — this will provide a rough estimate of how many miles away the storm is.

A storm that builds directly overhead might be less obvious until those pretty white clouds that were providing some nice shade moments ago turn a threatening hue of gray as rain dumps on you and the wind starts to howl or, worse yet, boom with thunder and lightning that are right on top of each other. Now is the time for a mad dash to the dock and shelter if close by. Like the National Weather Service says: “When thunder roars, go indoors!” You really don’t want to be on a boat struck by lightning. If out on open water or too far from shore and shelter, it’s time to hunker down and ride it out.

Caught in Thunderstorm on a Boat

Boaters who have been struck by lightning often begin their stories with “I was caught in this storm … ” before they share their miraculous or harrowing tales of survival and destruction (BoatU.S. has a number of first-person storm stories archived online: boatus.com/seaworthy/swthunder). Even though getting caught in a storm is not always avoidable, there’s still plenty that boaters can do to minimize the chance of a strike and lessen injury and damage if there is a strike.

How to Stay Safest in a Thunderstorm

We all learn in grade school that it is not safe to be outside during a lightning storm. We also learned that lightning seeks the highest point, and on the water that’s the top of the boat — typically a mast, antenna, Bimini top, fishing rod in a vertical rod holder or even the tallest person in an open boat. If possible, find a protected area out of the wind and drop anchor . If the boat has an enclosed cabin, people should be directed to go inside and stay well away from metal objects, electrical outlets and appliances (it’s a good idea to don life jackets too). Side flashes can jump from metal objects to other objects — even bodies — as they seek a path to water.

A Microwave Oven is a Faraday Cage

Lowering antennas, towers, fishing rods and outriggers is also advised, unless they’re part of a designated lightning-protection system. Some boaters also like to disconnect the connections and power leads to their antennas and other electronics, which are often damaged or destroyed during a strike or near strike.

Under no circumstances should the VHF radio be used during an electrical storm unless it’s an emergency (handhelds are OK). Also, be careful not to grab two metal objects, like a metal steering wheel and metal railing — that can be a deadly spot to be if there’s a strike. Some boaters opt to steer with a wooden spoon and keep their other hand in a pocket if forced to man the helm during a storm, while others like to wear rubber gloves for insulation.

Surviving Lightning Strikes While Boating

An open boat like a runabout is the most dangerous to human life during lightning storms, since you are the highest point and most likely to get hit if the boat is struck. If shore is out of reach, the advice is to drop anchor, remove all metal jewelry, put on life jackets and get low in the center of the boat. Definitely stay out of the water and stow the fishing rods.

If all goes well, the storm will blow past or rain itself out in 20 to 30 minutes. It’s best to wait at least 30 minutes until after the last clap of thunder to resume activities.

There’s a Zap For That

What to do when your boat is struck by lightning.

Knowing what to do in a storm and having the best lightning-protection system installed on the boat is by no means a guarantee that lightning won’t strike. The immediate checklist for a direct hit is very short:

1. Check for unconscious or injured persons first. If they’re moving and breathing, they’ll likely be OK. Immediately begin CPR on unconscious victims if a pulse and/or breathing is absent — there’s no danger of being shocked by someone just struck by lightning.

2. In the meantime, have someone check the bilges for water. It’s rare, but lightning can blow out a transducer or through-hull — or even just blow a hole in the boat. Plug the hole, get the bilge pumps running, work the bail bucket — whatever it takes to stay afloat. An emergency call on the VHF is warranted if the situation is dire. If the radio is toast, break out the flare kit.

If there are no injuries and no holes or major leaks below, just continue to wait it out. Once the danger has passed, check the operation of the engine and all electronics. Even a near strike can fry electronics and an engine’s electronic control unit, cutting off navigation, communication and even propulsion. Some boaters stash charged handheld VHF and GPS units and a spare engine ECU in the microwave or a tin box for this very reason. These makeshift Faraday cages have saved equipment.

One in 1,000 Boats Are Hit by Lightning Per Year

Obvious damage will need to be assessed and set right. Even those lucky enough to come away completely unscathed after lighting storms, with no apparent damage should have a professional survey done just to be sure. Minor damage to through-hulls can result in slow leaks, and all manner of electrical wackiness can emerge — sometimes much later. It’s best to catch these issues right away and get that information to the insurance folks for coverage.

Is Just a Ground Plate Enough?

On many levels, robust insurance coverage plays a huge role in your lightning-protection plan. Knowing how to avoid lighting storms and read the weather are certainly important, being ready for action in the event of a storm or strike is crucial, and an upfront investment in lightning protection can lessen destruction. When it comes to dealing with the aftermath of a damaging strike, however, extensive lightning strike coverage can’t be beat.

Take it from a luxury trawler owner who sustained more than $1 million in damage from a strike: “Boat insurance turns out to be the best investment we have made in the past 10 years!” he said. “We will never again grumble about writing a check for an insurance premium.”

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Lightning Protection

• Thread starter captcoho
• Start date Apr 9, 2022
• Forums for All Owners
• Ask All Sailors

After reading older and not so old threads, how many sailors favor grounding their mast and rigging ?  

Captain Larry-DH

I grounded my mast and rigging on my last boat. It was struck twice in 11 years. No hull damage, but a few rigging fittings showed scorch marks and were replaced as a precaution. Extensive electrical damage throughout the boat, both times. Melted VHF antenna both times. Does it attract lightning if you ground? Maybe. I can’t find anything conclusive on that question. I’ve heard of ungrounded boats that were struck too. I think a clear path to ground helps limit extent of damage if you’re struck, so I favor it for that reason. My new boat will be more challenging to ground, due to wire runs (catamaran) but I’ve already installed the Dynaplates. Connection on port side doesn’t have a path that can be totally hidden in unfinished areas, so I’m still thinking that one through. PS - Dynaplates do not explode from a direct strike. I’ve proven that by experience, twice. (I’ve read it on the web based on the theory that the porous metal can explode from internal steam pressure build up. Hogwash.)  

I don't. The fact that lightning is so powerful and unpredictable that it is deemed to strike where it may defies any attempts to control it. There are unproven theories about factors that may prevent or attract lightning strikes and increase or diminish the damage but the data does not support any. I have opted to observe the data regarding lightning strikes on boats and use this data to try to try and minimize the occurrence of a strike. A good and well stablished statistical fact is that the occurrence of loss of life due to a lightning strike on a sailboat is nearly nil year after year. (the same cannot be said for Golf Courses) That alone has removed any fear from sailing near lightning. Another statistical fact is that the majority of lightning strikes occur near land as opposed to open waters. I only really care about the boat getting hit by lightning if I am aboard; as when it is docked and unattended it will be protected by insurance. When sailing I will steer the boat away from land. It is also prudent to get away from a lee shore in the accompanying storm conditions. There are a few theories about "cone of protection", grounding the mast, installing diffusers but they are all at best unproven. Seems to me that the cone of protection and grounding of the mast are mutually exclusive as grounding may seem to attract lightning instead of repelling it. Both theories remain unproven so it would be a personal matter of choice as to which to follow by faith. Very fortunately, remember the odds against getting hurt are very favorably on our side.  

I do. My thinking is that a lightning strike is going to find the most direct way through the boat to the water. Either through a planned ground connection or possibly right through the hull, which could sink the boat. Either way, the electrical system and electronics would be fried, and fire is still a possibility from that, but providing a direct path to the water seems logical to me to minimize damage. As an architect, every tall building I designed was grounded with lightning rods, a proven invention we owe to Benjamin Franklin. An aluminum mast is effectively a lightning rod and the upper portion of Franklin’s system. It needs to be grounded as directly as possible to the water.  

We are fabricating a new 1/8" x 1.5" stainless steel grounding connector now to attach to one of our keelbolts.  

PaulK said: We are fabricating a new 1/8" x 1.5" stainless steel grounding connector now to attach to one of our keelbolts. Click to expand

Dalliance said: Mine may be a similar, less robust, approach. I have a copper ground wire from the aluminum mast base, down the compression post, to a stainless steel keel bolt almost directly below. External lead keel. Liberal application of Lanocote at the dissimilar metal connections. Click to expand

captcoho said: how many sailors favor grounding their mast and rigging ? Click to expand

I favor having the rigging grounded. A number of years ago a physicist friend of mine said a grounded boat is more likely to get hit, but less likely to suffer catastrophic damage. I don't know how reliable that info is, but I still go by it. My understanding is that lightning does not seek out a target. When it is ready to discharge it does so immediately through the least resistant path. So if that discharge moment occurs a hundred feet from your boat, chances are your 60 foot mast is not the most direct path. Additionally, the rigging provides the crew protection as, I think, it forms a Faraday cage. This is often referred to as the "cone of protection" referred to in Power Squadron materials. If you cruise or distance race you are going to get caught out in lightning at some point.  

Dalliance said: I do. My thinking is that a lightning strike is going to find the most direct way through the boat to the water. Either through a planned ground connection or possibly right through the hull, which could sink the boat. Either way, the electrical system and electronics would be fried, and fire is still a possibility from that, but providing a direct path to the water seems logical to me to minimize damage. As an architect, every tall building I designed was grounded with lightning rods, a proven invention we owe to Benjamin Franklin. An aluminum mast is effectively a lightning rod and the upper portion of Franklin’s system. It needs to be grounded as directly as possible to the water. [/QUO Click to expand

RoyS said: I have grounded my mast to my lead fin keel. Once while sailing a lightning bolt struck the water about a hundred feet from my boat. This led me to believe that my grounded mast did not attract lightning or that lightning bolt would have chosen my grounded mast instead of the water surface 100 feet away. Click to expand

To further add to the confusion, the oft repeated statement that electricity takes the path of least resistance is simply not true. Electricity takes all available paths. Proof of the latter statement is in any parallel circuit.  

There is no confusion on the SCIENCE involved on Lightning Avoidance [Protection is implies a Shield] You use SCIENCE to minimize your chances of being lightning's path to a Ground. This is True on Land or Water [Marina, On the Hard, or Open Sea for boats]. My best comparison of Land and Sailboats... "Water Towers and Sailboat Masts". The Science works for both examples. Be well Grounded. _____ This link has best info on Lightning and humor too. newbie lightning protection? But I will copy part of my post#5 here. _____ You never need a consensus on a SCIENCE ! However several types of sciences involved, thus the confusion. List in order of your ability to control them... 1) Electrical (flow of electrons) 2) Math (statistics) 3) Religion If you combine all 3 you can reduce your chances of being a target. In a nutshell... 1) Ground your boat and Isolate yourself 2) Buy Insurance 3) Pray it doesn't hit you ________ I will repost 2 pages from this book by Nigel Calder. Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems: Calder, Nigel: 9780071432382: Books - Amazon.ca Good Avoidance for your Boats... Jim...  

Attachments

• NIgel Calder Lightning-2.pdf 2.1 MB Views: 58

Found out some interesting things when working at a weapons disposal facility doing safety assessments, Lightening doesn't like to make "tight turns" and is highly unpredictable in the paths it takes, even with proper grounding. There is an NFP standard on lightning protection that is specific to buildings but has applications for us. First, although not stated explicity, the jist is that lightning takes the path it wants to take. For instance, with grounding straps and and these are big flat woven copper, not just small wires (and 10 gauge is small in terms of lightening) are run from the lightning rod to the ground along metal beams, the attachment point must be grounded to the beam. That is because even the robust straps cannot carry the current easliy and it will arch to the beam if not grounded. There is a specification for how sharp the bend can be in the ground strap since if you try to "turn" the lightning around too sharp a bend it will simply go off course and arc to the nest best available path. Think of a race car out of control around a 90 degree turn. Of course this is in common language rather than the techincal jargon of the standard. They also discuss in detail the concept of a "cone of protection" that effective lightning protection can provide. Take aways - I will ground my mast to the keel bolt of my lead keel to do what I can and trust in @JamesG161 solution list: BUT 1. I really doubt the little 10 gauge wire would conduct a lot of the current with a direct hit to the mast but it may do enough good to keep from blowing a hole in the boat. 2. The wire is insulated, but probably only good to about 600V and may very well arc right through that along the way. 3. There are probably several near sharp bends in that wire in its path from the mast to the keel bolt. 4. Insulate yourself as best you can, don't be hanging on the shrouds, backstay or hugging the mast during a lightning storm. Take advantage what cone of protection you do have. With any reasonable mast height the cone covers the whole boat. Probably why more lighning injuries on power boats - no cone of protection. 5. Make sure you are insured. Replacing electronics, a near certainty with a lightning strike may be expensive depending on your boat's equipment 6. Have a good relationship with your "Maker" - never hurts to be in good graces there. I had a lightning strike on my boat, BUT I wasn't even in the water. I was sitting in a travel lift awaiting launch the next morning and not "well grounded" to the water or the ground as far as I can determine. There were the nylon slings holding the boat, the huge rubber tires of the travel lift and the keel was resting on wooden blocks (not very good conductance). Go figure. My mast was about 75-80 feet in the air in the lift but there were other trees taller around. Don't know what that tells you about the advantages of being grounded to the water or not but it is what it is.  

smokey73 said: 1. I really doubt the little 10 gauge wire would conduct a lot of the current with a direct hit to the mast but it may do enough good to keep from blowing a hole in the boat . Click to expand

@JamesG161 Excellent point and something I didn't consider. As you stated, its not so much about "protection" as it is about "avoidance" in making sure the mast is at the same potential as the water. Also make sense now about the strike in the slings.  

smokey73 said: Also make sense now about the strike in the slings. Click to expand

I think I actually had what is sometimes called a "side strike". It hit somewhere else nearby and some portion "jumped" to my boat at the mast and it exited through the keel and the wet wooden blocks to the ground. The VHF antenna was "gone", the connection charred, the stuff at the top of the mast was laying in the cockpit, and all my electronics were damaged but there was no evident "exit wound" and no indication that wiring was damaged. Progessive was my insurance company and the were great! They required the mast be stepped and inspected to confirm it was a lightning strike and make sure everything was repaired. When they saw the black burn marks on the VHF antenna it was "lets get this fixed".  

I like the idea of chains from the boat to the ground. Are they connected to ground rods into the ground or just laying on the concrete or gravel?  

I believe ABYC recommends 6 gauge minimum (4 gauge is better) ground wire from mast base to keel bolt and 8 gauge minimum from chainplates, etc. to keel bolt. Of course connection to the keel bolt is only for external mounted keels, not encapsulated.  

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Lightning protection on sailboats is an un-researched area of knowledge.  Most of the information is based on the theoretical physics of lightning coupled with experiential and anecdotal evidence.  This doesn't mean we know nothing about the matter. The articles and links below pretty much cover the ground and I suggest you read them over before deciding the level and complexity of any lightning protection system for you boat.  Two things seem clear:

• You CANNOT make a boat lightning proof, nor even much reduce the chances of a strike.
• You CAN significantly improve the chance you and your equipment will survive a strike.

Recommendations for Lightning Protection provided by the American Boat & Yacht Council, Standard E4.  (KP44 website page)

Grounding Your Vessel . Technical articles and links on grounding: on the kp44.org website

Air Terminals (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant. 

Lightning & Sailboats . (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant Publication. 1992. Very good publication.

Articles and Letters on Lightning and Boats by Ewen M. Thomson.  Terrific resource for lightning info.

World Wide Opposition to ESE Lightning Rods   from National Lighting Safety Institute, May 13, 2003.  (Article dated 1999, by Abdul Mousa).

Considerations for Lightning Protection. A very excellent analysis of the problem.  Presented in the blog of Domino – a 65' power catamaran.

Forespar "Lightning Master" Static Dissipater .  Supposedly "leaks off lightning causing ground potential".  Mousa, Thomson  (above) and others disagree, saying the ground potential on structures below 300 meters is meaningless in terms of lightning strikes.  

Lightning Master Corporation .  Surge protectors and Dissipaters.  DIssipaters are pretty much shown to be ineffective, but surge protection for onboard electronics is important.

Marine Lightning Protection, Inc. Founded by Ewen M Thomson. Best information on the web. Provider of air terminals and lightning protection systems . In particular look at his page on Grounding and Sidearc™ electrodes which is currently state-of-the art.

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Is It Safe To Be On A Sailboat During A Lightning Storm?

Are you considering sailing during the nighttime during lightning storm season?

And you want to know how safe it could be if one experiences a lightning storm while on a sailboat.

Lightning storms can occur all year round but they are common during spring or summer seasons.

While storms are not entirely safe, it safer to be in the boat in this case a sailboat especially one with lightning protection on its mast when any type of lightning strikes.

Additionally, it is safer not to be or jump inside the water during a lightning storm as you can get electrocuted and you may not survive it.

In this guide, you will learn how safe it is to be in a sailboat during a lightning storm, what to do during a lightning storm while at sea, and the best lightning protection for boat masts.

How safe is it to be in a sailboat during a lightning storm?

It is quite safe however It is not as dangerous as you are imagining but only if you take necessary precautions beforehand.

Being in a sailboat during a lightning storm is almost safer than being on top of a very tall building or in your car during a storm.

It would be a good thing if you already have lightning protection also known as lightning conductors that extends from your masthead to the water.

Read: How Fast Do Sailboats Go?

This is because lightning storm strikes usually go straight down the mast, and then take the fastest route to the water.

So if the lightning protection doesn't extend to the water, the strike might go through the bottom of the boat and you would certainly get struck too.

Strikes from lightning storms are somewhat dangerous, statistically, 9 people out of every 10 people usually survive it.

However, the survival rate depends on the immediate medical attention administered as soon as the strike occurs.

What to do during a lightning storm while at sea

There isn't much one can do during a lightning storm, however, some precautions have to be taken to stay safe.

One of the few precautions to take during a lightning storm is to remain in the boat , never jump into the water.

The second one is to try not to get struck directly, this is rare but it can happen.

Thirdly, try not to panic so much as fear can make you jump overboard.

The fourth, avoid touching any kind of metal and electricals during a lightning storm.

It is also important to travel with a partner in case of any need for immediate medical attention like CPR before calling for medics.

A fire extinguisher is also necessary as fires are not uncommon during a lightning storm.

Finally, try to cover your ears as lightning storms could be detrimental to your hearing.

As I mentioned, there isn't much anyone can do during a lightning storm as it is a natural occurrence however you can take the aforementioned precaution to minimize damages.

The best lightning protection for boat masts

Lightning protection is also known as conductors is very important for minimizing damages caused by lightning storms.

Although it majorly protects the boat, it could protect you too from getting injured form the strike too.

One thing to keep in mind is the length of the conductor, a tall one is always recommended.

And EvoDis make the best lightning conductors at affordable rates and also with a 100% protection rate.

On a normal, sailboat masts look like they are most likely to get hit all the time during a lightning storm.

It depends on the size of the sailboat as the larger the sailboat, the less likely it will get zapped.

However, acting quickly will save you A LOT of trouble even though you do not have to do much during a lightning storm, just follow a few precautions that you can follow which I have listed above.

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Lightning Protection for Boats, Sailboats and Yachts – No More Lightning Strikes on Boats

No more lightning strikes,

No more damage on boats,, no more equipment loss.

Boats are extremely prone to lightning because the mast of the boat is highly conductive and it is usually the highest structure around. Even if the mast is made of a non-conductive material, salty sea water makes it extremely conductive.

During a storm, all positive charges on water climb up on the boat mast and emit towards the storm cloud. This process develops the lightning channel between the cloud and the mast, and lightning current flows down to the water through the mast, and damage all equipment on the mast and on the boat.

Lightning rod on boat mast

Lightning rods are invented more than 300 years ago to protect non-conductive buildings from lightning strikes. Conductive structures such as boat masts cannot be protected by lightning rods because the lightning rod attracts lightning strikes on itself and naturally to the mast.

Lightning current prefers to flow down through mast surface instead of a tiny conductor cable, and this results with damage on the boat and equipment on the mast.

Once again, lightning rods are invented to protect ordinary buildings, not conductive structures such as boats .

Lightning must be kept away from boats.

EvoDis® Lightning Prevention System

EvoDis® System Marine Series is the only lightning protection solution which dissipates the charges on the mast and makes the boats, sailboats and yachts “ invisible ” to lightning. This process keeps the surrounding electric field lower than the threshold level and avoids the development of the lightning channel between the cloud and mast.

Lightning acts as if the boat does not exist there and all equipment remain safe.

EvoDis® Lightning Prevention System protects more than 1300 sites all over the world with 100% success for the past 11+ years.

Contact Us today to protect boats from lightning strikes forever.

Best way of lightning protection is to stay away from lightning.

EvoDis® keeps lightning away from your boat.