lightning protection sailboat mast

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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.”

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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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MARINE LIGHTNING PROTECTION: Getting Z-Z-Z-Zapped on a Sailboat

I have to admit I don’t normally think about this too much. As is true of many sailors I suspect, I have subscribed to the philosophy that lightning and its effects are so random and poorly understood that you can get royally screwed no matter what you try to do about it. Which is a great predicate, of course, to going into denial and doing nothing at all. But the death in Florida last summer of Noah Cullen , a most promising young man who presumably was killed in a lightning strike while out singlehanding on his pocket cruiser, got me pondering this in a more deliberate manner. On doing some research, I found there are some hard facts out there that are well worth knowing.

Much of what we tend to learn about lightning is anecdotal, which mostly serves to make it seem more mysterious. I, for example, have never been struck by lightning, but I did once cut through some severe thunder squalls in the Gulf Stream in a grounded fiberglass boat and saw a bolt of lightning the size of a large tree trunk flash straight into the water just a few yards behind us. I can’t begin to tell you why it didn’t hit our nice 55-foot aluminum mast, and ever since then I’ve believed a strike is pretty much an act of God. It’s either going to get you, or not, and there’s nothing you can really do about it.

I have met a number of sailors who have been struck by lightning, mostly in grounded boats, and in every case they told me they lost all their electronics. So I have also always assumed there is nothing you can really do to protect installed electronics from a lightning strike.

But you should forget all the anecdotes you ever heard, at least temporarily, and think about the following:

Likelihood of a strike: It’s probably much higher than you like to think. One source states that a sailboat with a 50-foot mast will on average be struck once every 11.2 years. According to insurance data, the general average for all boats is about 1.2 strikes per 1,000 boats each year.  The average bill for damage is around $20,000. Most strikes are on sailboats (4 strikes per 1,000 sailboats each year). And these are likely lowball numbers, as it seems many lightning-strike victims are not insured or do not report the strikes to their insurers. According to one independent survey, unreported strikes could be as high as 50 percent of the total.

Location is also a big factor. Some areas, including very popular cruising grounds like Florida or Chesapeake Bay, are much more lightning-prone than others, and you are obviously much more likely to get struck when sailing within them. The overall average for reported lightning strikes on boats in Florida, for example, is 3.3 strikes per 1,000 boats each year, nearly three times the national average.

Map showing lightning strike probabilities around the world. The higher the number, the higher the probability

Interestingly, catamarans overall apparently are struck twice as often as monohulls. Could this be because they are effectively twice as much boat???

Preventing a strike: It really isn’t possible. There is no technology that can positively keep your boat from being hit. There’s seems to be little evidence, for example, that those silly little masthead bottle brushes some people put up are good for anything.

Spectacular image of a sailboat getting hit in Rushcutter’s Bay in Sydney Harbor, Australia, with inset images showing damage to the mast. Lots of other targets with masts around, so why did the bolt hit this one boat?

Limiting damage: This is where the action is. To paraphrase one writer: it is a fallacy to think in terms of “lightning protection.” What you want is “lightning control.” Which definitely means grounding your boat! An ungrounded boat is much more likely to suffer potentially disastrous damage when struck (i.e., holes in the hull, dead crew, etc.). A boat in fresh water is also much more vulnerable, because fresh water doesn’t conduct electricity as well as salt water. An ungrounded boat in fresh water is most vulnerable of all. If you’re on one of these during a strike, you may as well just forget about it and put a cap in your head.

Typical exit damage around an anchor well drain on a fiberglass boat. Hull damage just above the waterline is not at all unusual

Grounding your boat: The old school notion of leading a big copper strip from the base of your mast in a straight line to a single grounding plate on your hull is the process of being discarded in favor of a more sophisticated technique that connects the mast as primary conductor to a network of dissipating electrodes installed just above a boat’s waterline, the idea being in effect to make all of the boat’s hull something like a Faraday cage, so that the equipment and people within will be safer.

Example of a more modern grounding system

Note (I was particularly gratified to learn this): a metal hull is indeed a great ground, and the fact that it is painted, or coated in epoxy, or whatever, doesn’t change this. But you can still suffer significant damage on a metal boat!

Bonding: You and the gear on your boat are more likely to survive a strike without damage if the major bits of metal on your boat are bonded to the grounding system. This reduces the likelihood of dangerous side flashes. (It does, however, create complications with respect to the potential for galvanic corrosion on a boat.)

Saving electronics: First of all, stowing handheld electronics (or any disconnected electronics) in your oven will protect them during a strike. Just remember to take them out again before using the oven!

More importantly, you can protect installed electronics using various individual surge protectors, fancy spiral wiring, and other techniques I’m not going to pretend to understand, much less explain. See the sources below for more details.

Your personal safety: This should be most important, right? You want to stay off the helm if possible, stay below, stay dry, and don’t touch any big pieces of metal. All of which are easier said than done when you’re in the middle of a big squall! It would seem the most prudent tactic is severely reduce sail, or take it all down, pop the boat on autopilot, and get below well in advance of and after a thunderstorm.

Lightning and Sailboats : Academic paper published by Ewen M. Thomson, currently recognized as the most well-informed go-to guy on this subject.

Marine Lightning Protection : Website for a business run by Ewen Thomson (see above), who is a pioneer in modern cage-style boat-grounding techniques. Thomson will ground and bond your boat for you, if you like, but there’s also lots of useful raw info in here.

Lightning Survey Results : Discussion re results of a small independent online lightning-strike survey conducted by a cruiser who owns a power-cat named Domino . Very informative.

Considerations for Lightning Protection : Conclusions reached post-survey by the owner of Domino , referenced above.

Lessons in Lightning : Ocean Navigator article by a cruiser in an aluminum boat who was struck by lightning in the Baltic. Of particular interest to those (like myself) who own aluminum boats.

There are lots of other resources out there, but these four links are a very good place to start. You’ll find many other valuable sources just by reading through these articles and following the links within.

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STORM PORN: Casco Bay Thunder Squall

We were hit by lightning in a fast moving front off Newfoundland many years ago (before gps). All the electronics were fried! The binnacle must have been demagnetized as it hopelessly spun in circles, giving us only a hand sighting compass to steer by. The smell of burned wire insulation in boat was overpowering. Luckily this is a rare occurrence and for the most part just bad luck!

@Robert: Interesting. In Bermuda once I met a tall ship, steel hull, that had been struck by lightning, and as a result the whole ship was magnetized. Which also kept their compasses from working properly. They were on their way to Norfolk, Virginia, to get degaussed.

I feel obligated to take issue with a fair bit of what’s been said above. Without writing a textbook, the following is best seen as “almost correct”. If you consider that the sky has a positive electrical charge and the sea a negative charge, grounding the boat and the mast gives them a negative charge. Hence as far as the lightning is concerned, the bonded mast raised the local sea level to mast top height. Lightning will tend to bridge the narrowest gap with the greatest electrical charge difference – so by grounding boat and mast, you have made them MORE vulnerable to lightning strikes, not less. In other words, NOT grounding the boat and mast will REDUCE your chances of being struck.

Tying an earth system into the keel bolts is not likely to result in loss of the keel, but it sure does constitute trying your best to do so. If the bolts are electrically weak they may act as a fuse and “blow” during a strike.

Making a Faraday shield form shown above does help mitigate the effects of the strike compared to a simple bonding of the mast to the keel in many situations, but it’s over-rated. In a big strike, lightning will try to follow a straight path and the energy contained in such a strike is often too great for a simple system to be effective. And it needs to be understood that either method makes the strike a whole lot more likely to occur.

A grounded mast does offer a degree of protection to a non-bonded electrical system in the boat underneath. There is what’s termed a “cone of protection” extending downwards at 30 degrees from the top of the mast. This is the standard system used in telecommunications.

The best protection you can have is to park your ungrounded wooden boat with a wooden mast and an electrical system isolated from the sea, right next to a grounded metal boat with a big aluminium mast. In the photo above depicting the Sydney harbour yacht being struck, the question was posed “why did the bolt hit this one?” The answer is that it was best grounded boat in that area.

@Bryan Tuffnell while part of what you say is true that a grounded boat is more likely to be struck the catch is that it will do less damage if struck where as a boat not grounded is less likely to be struck if it ever is you will have significantly more damage

Maybe, but quite likely not. The only way to offer lightning protection is to place a grounded lightning target above the mast, but electrically isolated from the mast and every other part of the boat. The grounding is completely independent of the mast, rigging, interior, electrical system, and above waterline areas of the hull. The idea is that this attracts the lightning and provides a low impedance path to ground, without drawing the charge into any part of the boat or its contents. Using this strategy one does not ground the mast, hull, rigging, etc. This is the only strategy to apply if one insists on lightning protection.

the sky has a positive electrical charge and the sea a negative charge

Its the other way round. When polarity builds up the negative charge is at the cloud base, and the positive at the sea surface. [quote=Bryan TuffnellNOT grounding the boat and mast will REDUCE your chances of being struck[/quote] Wrong – the enormous voltage actually doesn’t care if you’re grounded or not. Given the fact that the boats surface will always be wet or moist in some way it is “grounding” enough to raise the sea level polarity up to the mast top. The only thing proper grounding does is trying to guide the current of a charge in a way that does the least harm.

Not necessarily in the first case, and generally not true in the second… the polarity of lightning is variable, and there are countless examples of nearby strikes to ungrounded boats. Obviously if lightning didn’t care of you were grounded or not, lightning conductors wouldn’t work.

As far as doing the least harm goes, grounding the mast is about the worst thing you can do, particularly if you have grounded electrical items onboard.

Our boat (20′ cruiser) has no grounding system. Is it foolish to think that the method where a set of jumper cables is attached to mast and other end dropped overboard, might be a good emergency strategy if caught in elec storm?

what a topic indeed. to protect or not to protect, that is the question. simply do you use a brush type or spike type diffuser on your mast, do you protect for side strikes, or stay central with mast bonding.. im trying to find an answer like us all and so far , the answers all differ..

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Protect Your Boat from Lightning

If there is anything equally as scary to an ocean sailor as falling aboard, it is the highly unlikely yet still extant possibility of being struck by lightning at sea. Like a giant battery in the sky, the negative post on that wispy, amorphous blob of a cloud is always looking for the shortest path to ground, which in this case means the highly conductive saltwater on which you are sailing—or the highest conductive point on your boat.

So there you are sailing along, listening to Jimmy Buffet on the stereo, blissfully unaware of the big cloud’s intentions as it aims its spear of lightning at the highest electrically charged point on your vessel, which we hope is not you or a fellow crew member. Fortunately, the odds of your being struck by lightning are slim, particularly on the West Coast. The odds are significantly higher on the East Coast, particularly in Florida and on Chesapeake Bay, yet still minimal. A full 33 percent of all lightning insurance claims in the U.S. are from the Sunshine State, where the lighting strike rate is 3.3 vessels per thousand as opposed to an average 1:1,000 throughout the rest of the country.

As you may well imagine, the majority of boats hit by lightning are sailboats and for an obvious reason: aluminum masts offer a close point of contact from the cloud and a quick ground path through ocean water splashed on the deck and hull. If your deck shoes are soaked with saltwater while you are ambling along a side deck, you could become a human light bulb for a tiny fraction of a second. In most cases of boats hit by lightning, crew are not directly affected, and of those who are, roughly 90 percent survive.

Notwithstanding the low chance of being hit by lightning and the high survival rate of lightning attacks, it is imperative that we as offshore sailors do everything possible to prevent damage in the event of a lightning strike. Fortunately, a number of manufacturers offer devices to protect our valuable onboard electronics, if not ourselves, from the ravages of lightning.

The first step in protecting your boat from lightning is bonding all thru-hulls with copper wire. This includes all bronze mushroom fittings for engine raw water intake, deck drains, standing rigging, windlass, bow roller and so on. The more dissipation surface you expose to a lightning strike, the less likely your vessel and electrical system are to incur serious damage.

You will also need to install a grounding plate, or zinc anode, to the bottom of the hull and connect the grounding system to a bolt on the grounding plate inside the vessel. Regardless of whatever other device you install to dissipate or absorb lightning energy, the traditional thru-hull grounding plate is still a necessary yet inexpensive device to save protect your vessel. Every time you haul out your vessel for bottom painting, be sure to exchange the worn-out chunk of zinc for a new one. 

The traditional lightning protection device for boats is the old-fashioned lightning rod, which can still be found on the mastheads of many yachts. Forespar, L-Com and Rohn Products are some of the market leaders in this traditional form of lightning protection. Priced at under $100, even the humblest of sailors can enjoy some degree of protection from lightning strikes on their vessels.

A more recent variation of the masthead rod is a lightning static dissipater, which looks like a metallic dust broom mounted upside down on a sailboat mast. As comical as they may look, those frizzy lightning dissipaters could save your onboard electronics and conceivably your life if installed correctly.

Mounted next to the masthead light, a dissipater is, first of all, the highest point of contact for potential lightning. Because the thin wire strands are so thin and numerous, the surrounding air absorbs the electrical charge immediately, saving everything below that point from damage.

You can find the Forespar Lightning Master for under $200 online, and installation is fairly easy. First of all, since the device is self-contained, it is not connected to any cable leading down to a submerged lead or anywhere else. Installation involves little more than a small stainless steel bracket on the masthead. The Lightning Master may also be mounted on the bridge of a large motorboat.

A more sophisticated device used to protect a boat’s electrical system and sensitive electronics is a microprocessor-controlled shunt, which immediately shorts out excess amperage, drawing the energy into itself and out to a large load where the electrical impulse dissipates when lightning strikes. By absorbing the huge surge of electricity in a fraction of a second, the shunt prevents current from reaching sensitive electrical and electronic equipment.

EMP Shield, named for “electromagnetic pulse,” is an industry leader in lightning control technology, manufacturing shunts for business, home and vehicle/vessel. The shunts are designed for specific applications and anticipated amperage levels, whether they are engine and generator power cables, radio and navigation systems, solar panels or other sensitive fixtures.

EMP Shield’s line of vehicle and vessel shunts include 12V/24V shunts to protect the majority of large systems on your vessel, while their inline VHF antenna shunts are small enough to be mounted anywhere along the antenna cable and tucked away neatly inside the mast or below decks.

For a device capable of protecting larger systems, consider one of EMP’s three-phase models designed to protect starter motors, generators and large battery banks. Incredibly, most of EMP Shield’s shunts are priced under $500, well within the budget of the humblest of offshore and coastal cruisers.

Protecting vessel, crew and sensitive onboard systems from lightning strike will give you ease of mind while you are underway, particularly in tropical regions where lightning is common. Make sure your vessel’s thru-hulls and standing are bonded, and consider investing in a microprocessor-controlled shunt for added protection against lightning. Knowing your vessel is safe from lightning strikes will give you ease of mind while underway or at anchor in lightning-prone areas. n

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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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Boating- Lightning Protection

Those who enjoy Florida's waters certainly should understand the phenomena of thunderstorms--lightning and the precautions to take in order to keep these activities pleasurable--and how to prevent tragedy.

While this phenomenon is occurring in the clouds, a similar phenomenon is occurring on the surface.

Negative charges repel negative charges and attract positive charges. So, as a thunder cloud passes overhead, a concentration of positive charges accumulates in and on all objects below the cloud. Since these positive charges are attempting to reach the negative charge of the cloud, they tend to accumulate at the top of the highest object around. On a boat that may be the radio antenna, the mast, a fishing rod, or even you! The better the contact an object has with the water, the more easily these positive charges can enter the object and race upward toward the negative charge in the bottom of the cloud.

Lightning occurs when the difference between the positive and negative charges, the electrical potential, becomes great enough to overcome the resistance of the insulating air and to overcome the resistance of the insulating air and to force a conductive path between the positive and negative charges. This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch!

Lightning strikes represent a flow of current from negative to positive, in most cases, and may move from the bottom to the top of a cloud, from cloud to cloud, or most-feared, from cloud to ground (see Figure 3). And when the lightning does strike, it will most often strike the highest object in the immediate area. On a body of water, that highest object is a boat. Once it strikes the boat, the electrical charge is going to take the most direct route to the water where the electrical charge will dissipate in all directions.

A second example is a sailboat. Lightning strikes the mast. The electrical current follows the mast or wire rope to your hands, through your body to the wet surface, and then through the hull to the water.

Or, while operating a motor boat, the lightning strikes you, passes through your body to the motor, and then to the water.

Or, sitting in your aluminum or fiberglass rowboat, you are holding a graphite (a good electrical conductor) fishing rod. The rod is struck by lightning. The electrical charge passes through the rod, your body, then to the boat to the water.

In all four examples you could be seriously injured. You could be dead.

Watch for the development of large well-defined rising cumulus clouds. Once they reach 30,000 feet the thunderstorm is generally developing. Now is the time to head for shore. As the clouds become darker and more anvil-shaped, the thunderstorm is already in progress.

Watch for distant lighting. Listen for distant thunder. You may hear the thunder before you can see the lightning on a bright day. Seldom will you hear thunder more than five miles from its source. That thunder was caused by lightning 25 seconds earlier. The sound of thunder travels at one mile per five seconds (see Figure 4).

But small boats are seldom made of metal. Their wood and fiberglass construction do not provide the automatic grounding protection offered by metal-hulled craft. Therefore, when lightning strikes a small boat, the electrical current is searching any route to ground and the human body is an excellent conductor of electricity!

Today's fiberglass-constructed small boats, especially sailboats, are particularly vulnerable to lightning strikes since any projection above the flat surface of the water acts as a potential lightning rod. In many cases, the small boat operator or casual weekend sailor is not aware of this vulnerability to the hazards of lightning. These boats can be protected from lightning strikes by properly designed and connected systems of lightning protection. However, the majority of these boats are not so equipped.

If you are considering the purchase of a new or used boat, determine if it is equipped with a properly designed and installed lightning protection system. Such a system is generally more effective and less costly than a system installed on a boat after it has been constructed.

The mast, if constructed of conductive material, a conductor securely fastened to the mast and extending six inches above the mast and terminating in a receiving point, or a radio antenna can serve as the air terminal.

The main conductor carries the electrical current to the ground. Flexible, insulated compact-stranded, concentric-lay-stranded or solid copper ribbon (20- gauge minimum) should be used as the main conductor.

The ground plate, and that portion of the conductor in contact with the water, should be copper, monel or navel bronze. Other metals are too corrosive. The secondary conductors ground major metal components of the boat to the main conductor. However, the engine should be grounded directly to the ground plate.

Lightning arrestors and lightning protective gaps are used to protect radios and other electronic equipment which are subject to electrical surges.

The connectors must be able to carry as much electrical current as other components of the system. Further, the connections must be secure and noncorrosive.

On a large power boat or sailboat, a properly designed and grounded antenna could provide a cone of protection. Presently, however, the vast majority of the radio antenna is totally unsuitable for lightning protection. This is also true of the wires feeding the antenna. If the antenna is not properly grounded, it may result in injury or death and cause considerable property damage.

Ideally, an effective ground plate should be installed on the outside of all boats when the hulls are constructed. Unfortunately, this is not often done. Such a ground plate would help manufacturers design safer lightning protection systems for the boats.

• A lightning protective mast will generally divert a direct lightning strike within a cone-shaped radius two times the height of the mast. Therefore, the mast must be of sufficient height to place all parts of the boat within this cone-shaped zone of protection (see Figure 6).
• The path from the top of the mast to the "water" ground should be essentially straight. Any bends in the conductor should have a minimum radius of eight inches (see Figure 7).
• Major metal components aboard the boat, within six feet of the lightning conductor, should be interconnected with the lightning protective system with a conductor at least equal to No. 8 AWG copper. It is preferable to ground the engine directly to the ground plate rather than to an intermediate point in the lightning protection system.
• If the boat's mast is not of a lightning protective design, the associated lightning or grounding connector should be essentially straight, securely fastened to the mast, extended at least 6 inches above the mast and terminate in a sharp receiving point.
• The radio antenna may serve as a lightning protective mast, provided it and all the grounding conductors have a conductivity equivalent to No. 8 AWG copper and is equipped with lightning arrestors, lightning protective gaps, or means for grounding during electrical storms. Most antennas do not meet these requirements. The height of the antenna must be sufficient to provide the cone-shaped zone of protection.
• Antennas with loading coils are considered to end at a point immediately below the loading coil unless this coil is provided with a protective device for by-passing the lightning current. Nonconducting antenna masts with spirally wrapped conductors are not suitable for lightning protection purposes. Never tie down a whip-type antenna during a storm if it is a part of the lightning protection system. However, antennas and other protruding devices, not part of the lightning protection system, should be tied down or removed during a storm.
• All materials used in a lightning protective system should be corrosion-resistant. Copper, either compact-stranded, concentric-lay-stranded or ribbon, is resistant to corrosion.
• The "water" ground connection may be any submerged metal surface with an area of at least one square foot. Metallic propellers, rudders or hull will be adequate.
• On sailboats, all masts, shrouds, stays, preventors, sail tracks and continuous metallic tracks on the mast or boom should be interconnected (bonded) and grounded.
• Small boats can be protected with a portable lightning protection system. This would consist of a mast of sufficient height to provide the cone of protection connected by a flexible copper cable to a submerged ground plate of at least one square foot. When lightning conditions are observed in the distance, the mast is mounted near the bow and the ground plate dropped overboard. The connecting copper cable should be fully extended and as straight as possible. The boaters should stay low in the middle or aft portion of the boat.
• Stay in the center of the cabin if the boat is so designed. If no enclosure (cabin) is available, stay low in the boat. Don't be a "stand-up human" lightning mast!
• Keep arms and legs in the boat. Do not dangle them in the water.
• Discontinue fishing, water skiing, scuba diving, swimming or other water activities when there is lightning or even when weather conditions look threatening. The first lightning strike can be a mile or more in front of an approaching thunderstorm cloud.
• Disconnect and do not use or touch the major electronic equipment, including the radio, throughout the duration of the storm.
• Lower, remove or tie down the radio antenna and other protruding devices if they are not part of the lightning protection system.
• To the degree possible, avoid making contact with any portion of the boat connected to the lightning protection system. Never be in contact with two components connected to the system at the same time. Example: The gear levers and spotlight handle are both connected to the system. Should you have a hand on both when lightning strikes, the possibility of electrical current passing through your body from hand to hand is great. The path of the electrical current would be directly through your heart--a very deadly path!
• It would be desirable to have individuals aboard who are competent in cardiopulmonary resuscitation (CPR) and first aid. Many individuals struck by lightning or exposed to excessive electrical current can be saved with prompt and proper artificial respiration and/or CPR. There is no danger in touching persons after they have been struck by lightning.
• If a boat has been, or is suspected of having been, struck by lightning, check out the electrical system and the compasses to insure that no damage has occurred.
• Boating in Florida's waters is an enjoyable activity for many people. Keep it that way!
• Listen to the weather reports! Learn to read the weather conditions. Heed these reports and the conditions. Stay off or get off the water when weather conditions are threatening.
• Install and/or maintain an adequate lightning protection system. Have it inspected regularly. Follow all safety precautions should you ever be caught in a thunderstorm. By using good judgment, it is less likely that first aid or CPR will be needed while boating.
• National Fire Codes. Lightning Protection Code--NFPA 78; Fire Protection Standard for Motor Craft--NFPA 302, 14. National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.
• Standards and Recommended Practices for Small Craft. Standard E-4, Lightning Protection. American Boat and Yacht Council, P.O. Box 806, Amityville, NY 11701.
• Sitarz, Walter A. Boating Safety--Thunderstorms (MAP-5), Florida Sea Grant College Program, University of Florida, Gainesville, FL 32605.

William J. Becker, Professor and Extension Safety Specialist, Agricultural Engineering Department, Cooperative Extension Service, Institute of Food

Publication #: SGEB-7 October 1992

Disclaimer and Reproduction Information: Information in NASD does not represent NIOSH policy. Information included in NASD appears by permission of the author and/or copyright holder. More

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Lightning Protection - Wood mast

Discussion in ' Boatbuilding ' started by M&M Ovenden , Jul 31, 2016 .

M&M Ovenden Senior Member

Hi, Any experience running lightning conductors in a wood mast ? We will have a gaff rig, so no sail track. We will probably laminate a mast up, so it would be possible to run a conductor in the center, but I'm somewhat worried about heating and having the mast "explode" if hit. I'm considering having a conductor laminated in above the hounds, and connect it to one of the shrouds, but most standards say a "continuous" conductor. Thoughts ? Comments ? Suggestions ? Cheers, Mark  

PAR Yacht Designer/Builder

The mast will not explode. Areas of concern are; connections and hard angle changes in direction and where it passes through things, like decks, bulkheads, etc. This are places the arc can jump, which will act much like an explosion. The idea is a continuous, as straight as practical run from masthead to ground plate. This directs the path straight to earth, which is what you want. FWIW, a gaffer without a track isn't very likely to get struck, but if you must, you can cut a rabbet (most common) and bury the conductor or put it inside the mast.  

CDK retired engineer

M&M Ovenden said: ↑ Hi, Any experience running lightning conductors in a wood mast ? We will have a gaff rig, so no sail track. We will probably laminate a mast up, so it would be possible to run a conductor in the center, but I'm somewhat worried about heating and having the mast "explode" if hit. I'm considering having a conductor laminated in above the hounds, and connect it to one of the shrouds, but most standards say a "continuous" conductor. Thoughts ? Comments ? Suggestions ? Cheers, Mark Click to expand...

mydauphin Senior Member

True but I have many a bust wood mast from lighting, may be it is all stuff people put on them like antennas, stays, lights. I would either put nothing at all on mast which defeats it's purpose, or a big welders cable from top to the ground on hull. But lighting though rare can be devastating. I saw a boat on the hard with a hole on its side, some one painted over the ground and voltage decide to remove it.  

Hi, I'd like to bump this thread again and see if there are any opinions considering the use of synthetic shroud material. This would mean no real conductive material overhead for protection. Thoughts, comments ? Cheers, Mark  

tom28571 Senior Member

It appears that lightning does pretty much what it wants to based on physics of the particular situation, which is seldom understood well enough for humans to predict. Wood masts can certainly be struck by lightning just as trees are commonly hit. If the mast is reasonable dry an interior or exterior conductor will likely reduce the damage of a strike. Paul is right about avoiding sharp or even small radius turns in the conductor but it might help to understand why. A turn or bend in a conductor acts like an inductance which acts like resistance to high frequency current. While a lightning strike may seem to be a DC current, it will have an extremely sharp leading edge followed by a slower decay which contains all frequencies. That is why a strike is always picked up by radio receivers. A poorly made splice or connector will be a point of resistance and may heat up and explode if subjected to a large current. If the bend or arc in the conductor occurs near anything that is grounded the resistance of the bend and the capacitance between the conductor and ground will allow an arc to ground through the low resistance of the capacitance. Consequently, running the conductor along the inside of a hull below the waterline is a common invitation to holes in the hull from a strike. As an engineer often working with systems exposed to lightning, I found that it was a difficult taskmaster and predicting accurately the result of protective efforts was sometimes a sobering realization of our imperfect knowledge.  

SamSam Senior Member

I've read in a number of places to only use braided wire, but this is the only explanation I've seen for why it's braided. Also, it's never covered in an insulator like welding cable is, and it's not recommended to even paint it. I think the braiding also helps keep the wires all together, since they aren't covered and held together with anything. Lightening protection seems a bit like black art or voodoo, so it might be a good thing to google 'lightening protection for boats' . Also, scroll down to the bottom of this page for 'similar threads', there have been a number of discussions. (23) Technical facts: Lightning Travels on the surface of the Lightning Rods and cable. The many strands in the specially designed braided cable adds greatly to it’s surface area. The BRAIDING in the Lightning Cable is very important as it has the effect of cancelling the Electro Magnetic Pulse (EMP). As current travels down each braided strand of wire and since the strands “cris-cross” each other, and “like charges repel”, The braided cable has the effect of cancelling the EMP. Compared to regular electrical wire, the EMP around regular wire can couple with other wires under roof and behind walls and can transfer very high voltages into the electrical wiring. EXCEPTION: On structural steel buildings and below ground, un-stranded cable of sufficient size is ok since the EMP will be absorbed by the steel in the structure and in the earth. http://www.lightningrodsupply.com/index_files/page0008.htm  

Braided wire does may have some advantages at higher frequencies but I'd need to see some objective testing to know whether the overall effect is positive or negative for lightning protection. Higher frequencies do tend to run on the surface of a wire but all those loops do represent a lot of inductive resistance to high frequencies. I've not heard of using braided wire in lightning protection. I would personally prefer flat straps as probably having the most effective surface area per unit of conductor and the least inductance when run straight. Lightning is dark magic so I may be wrong. The reason paired communication wire is twisted is that each twist represents a "loop" that generates a field in opposite direction to its neighbor and the induced currents tend to cancel each other. The effect is the same whether transmitting or receiving.  

Hi, Any thoughts on running a large lightning conductor inside a wood mast? I'm wondering if anybody else has done this. thanks ! Mark  

Inside the mast is just asking for a significant fire potential.  

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yea, fire is my worry. In theory we have an ok idea of the lightning waveform, and could size accordingly, but the unknowns of terminals/connections means anything could happen. I'm considering running a 2/0 cable (much bigger than the 4awg normally spec'd) to solid copper bar to exit the mast at the top/bottom for other connects (drill/tap it for taking a lug). This would produce a couple sharp bends. It seems that if a wood mast is hit, it's not a good situation, so maybe doing this offers better protection at least for the crew on deck. I'm going to be laminating the mast in about a month, so I have time to stress about this a bit. Moving from wire rope to synthetic standing rigging changes the game. Cheers, Mark  

I want to build a class lightning

dyneema and lightning...

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Lightning + Mast = ????

• Thread starter Slow Mo^cean
• Start date Jul 15, 2012
• Forums for All Owners
• Ask All Sailors

Slow Mo^cean

Has anyone had experience with lightning hitting their mast? We got caught out in a surprise super cell storm today with some heavy rain and lots of lightning. Luckily we weren't hit, just soaked. When it got really bad, I abandoned all hope of trying to motor back to the ramp, dropped anchor and went below. We had lightning all around us and my wife and I couldn't help think what would happen if we were hit by lightning. My biggest fear was it travelling down the side stays and into the cabin. Just wondering what the best thing to do is if we happen to be caught in the same storm again.  

Ive been hit several times. If the boat is well bonded (all metal objects electrically connected by heavy wiring, etc.) and there is an 'easy' pathway overboard for the lightening strike then there typically wont be much structural damage, other than 'fried' electronics. There has been a continual 'shift' in the current thinking of how to keep lightening out of the inside of a boat. Here's the probable latest thinking on the subject: http://www.marinelightning.com/ The person who runs this corporate entity was the famous 'lightning guru' at the University of Florida and his recommendations for marine protection then were probably the most sought after in the entire country. Apparently his thinking has evolved since his retirement to start a commercial marine lightning protection company - multiple 'sideflash' electrodes installed along the boats waterline, etc. etc. to help get the strike 'out' of the boat.  

not long after I sold my Spirit 23 to a friend, he was hit .. Wife was inside the cabin .. the light bulbs inside and in the navigation lights popped .. She was not hurt.. He was at the tiller and also was not hurt.. The lightning did jump from the chainplates and out the hull.. It vaporized the resin in a couple of spots below the waterline leaving a gauze of fiberglass cloth that wept water .. He was able to manually pump and got the boat back to the boatyard and on the hard so she would not sink. It was repaired and no other problems were noted.. engine had a non-electronic ignition system, and there were no electronics on board when they were struck..  

i often think the path the lightening will take is from the mast to the bottom of the mast then bursting sideways through me on the way to the outboard as im on the tiller .. regardless i am going to connect the mast to my drop keel with #4 wire and my shrouds and forestay with #6 to my keel or a seperate large conductor that i can put in the water. i am going to try for wiring that can be non permanent but quick to "hook up" i want to be able to pull the sails,throw anchors,hook up ,lift outboard and get in the cabin...lol..  

Back when we were doing a lot of J-24 racing. Sometimes we would get caught out in some pretty nasty lightening storms. We would connect the spinnaker pole and drop the other end into the water and then hunker down pray and wait it out.  

You take some of your mooring chain, wrap it round your mast, drop the other end into the water. Then unhook your VHF, and MF radio if you have one. You stick any electronics such as walkie talkie or epirb, in the oven (which is a faraday cage) Then you hope you dont get hit. If you have a carbon fiber mast, then good luck, those things explode when hit. I have sailed right through a lightening storm, and not been hit, i think its a tiny chance you ever will be hit. What i thought in the first storm, was my boat is the highest thing around, but if you think of it, if the lightning comes from right above you, then your boats mast is the closest thing to the earth, but unless it right above you, your thirty foot mast is not the closest thing, if its off to your side, lightening takes the shortest path, if its a hundred yards to your side, then the shortest path is still into the sea. To hit your mast, means it has to travel, a longer distance.  

Douglast said: ...I am going to connect the mast to my drop keel with #4 wire and my shrouds and forestay with #6 to my keel or a seperate large conductor that i can put in the water. Click to expand

I like the jumper cable idea. I think from now on, I'll carry a set or two and connect one to the mast and one to one of the stays.  

Slow Mo^cean said: I like the jumper cable idea. I think from now on, I'll carry a set or two and connect one to the mast and one to one of the stays. Click to expand

Were I you guys, I would really research the idea of chains and jumper cables....they are way too "iffy" a connection to provide ANY safety..read high resistance path, link gap, connectivity, current capacity of chain link and jumper cables, add wet to the above...etc else Darwin will have his way.... You can actually make the chances of a hit better, or worse disturb the "natural" shedding provided by the design of the boat... All that being said, it is your boat and your butt...but don't be surprised if you get a hit and the insurer does not pay....anything....for your efforts. YMMV  

KD3PC said: Were I you guys, I would really research the idea of chains and jumper cables....they are way too "iffy" a connection to provide ANY safety..read high resistance path, link gap, connectivity, current capacity of chain link and jumper cables, add wet to the above...etc You can actually make the chances of a hit better, or worse disturb the "natural" shedding provided by the design of the boat... Click to expand

kenn said: Um, what? Do you speak from experience, or are you thinking out loud, like the rest of us are? What is this "natural" shedding that is part of the boat design? Click to expand

kenn said: I do have an electrical background, and I've tried to stay current with the issue of lightning hitting boats, and the possibilities for protection. The common denominator of most solutions is that you try to offer an easy path from the masthead to the water, that will minimize injury to occupants and damage to the boat. Click to expand

kenn said: Referring specifically to our small trailer-sailor, real no-sh1t 100% effective lightning protection is prohibitively expensive and not justifiable. The preferred solution is to not be in the boat during lightning. But IF we are caught out in lightning, all we can do is to make it easier for lightning to get where it wants to go via the outside of the boat, while we remain a bit safer inside the boat. Click to expand

kenn said: If the choice is between nothing (which means any lightning hit will have to arc the last few inches to the water, and is therefore unpredictable; could burn someone or hole the hull) , and doing the chain or jumper-cable thing (which offers it a much lower-impedance, outside connection to the water), yoiu can guess what I'll do. Click to expand

kenn said: If you have a better solution, please let's have it. Click to expand

KD3PC said: ...I posit that the easiest way for the current to dissipate is to follow that more robust path of masthead, shroud, chainplate and jump to ground...multiple poorer paths will do nothing except explode when the current attempts to take that weak path and jumps to a more appropriate path. Click to expand

a chain with marginal continuity, questionable conductivity and a casual attachment, will offer nothing as far as conductivity of high current. Those links merely touching do nothing. Similarly a jumper cable with a large alligator clip is not a connection, it is merely a high resistance short, as will be the marginal connection of a couple of wraps of chain around the mast. Click to expand

There is NO full time, safe solution to a direct lightning strike. The current is going to ground as quickly as possible, and there is NO predictable path. You may comfort yourself with these actions, as well as those of the U FL expert...at greater cost, but they will do nothing to guarantee the path and how it exits the boat. Click to expand

Something like this http://zenpole.com/Zenpole_tech_picture_brochure_rev6.pdf (project got stalled because of the cost of liability insurance required for licensing the patent from Dr. Thomson/ U of F)  

kenn said: ....Taking all your points into consideration, what would you then think of an arrangement similar to the jumper cables, using say #2AWG welding cable, where the connection to the mast is a high current quick-disconnect of some type, and the in-water end is a suitable sized copper bar or plate?... Click to expand

Sumner said: One possible alternative for the trailer sailor is the ZenPole system (just noticed Walt posted as I was writing this)... http://zenpole.com/ ...if it comes to market. It is based on the technology mentioned in Rich's post on taking the lightning charge to the water's surface where lightning strikes in nature and not trying to dissipate the charge down in the water (which is real hard to do in fresh water). It uses electrodes that are designed with the trailer sailor in mind. Ruth and I had a prototype on our boat but luckily never got to test it. We have been in... ..... some really bad lightning on a couple trips though before having the ZenPole on the boat. Here are some pictures and why we believe in it enough to use it ... http://purplesagetradingpost.com/sumner/macgregor2/outside-43.html ... and like MS said these systems aren't designed to stop a strike and the statistics don't show that they attract a strike. They are there to hopefully lessen the damage, especially to occupants and to prevent holes from being blown in the vessel. I was going to go the chain or jumper cable route a year or two ago, but after reading felt that it would not do much, especially in fresh water where we are most of the time when on the Mac, Sum [FONT=Arial, sans-serif] ============================ [/FONT] Our Endeavour 37 Our MacGregor 26-S Pages Our Trips to Utah, Idaho, Canada, Florida Mac-Venture Links Click to expand

It seems like a lot of the debate here is the worry about losing a chain or set of jumper cables to amperage overload. To me, I could care less if a $20 pair of jumped cables or chain gets smoked, as long as the lightning travelled through it instead of me or a family member on board. My biggest fear is the lightning travelling through a stay and into a chainplate, which is inches from somebody's head in the cabin..  

Slow Mo^cean said: It seems like a lot of the debate here is the worry about losing a chain or set of jumper cables to amperage overload. To me, I could care less if a $20 pair of jumped cables or chain gets smoked, as long as the lightning travelled through it instead of me or a family member on board. My biggest fear is the lightning travelling through a stay and into a chainplate, which is inches from somebody's head in the cabin.. Click to expand

Mark Maulden

A severe lightning strike is considered in the aircraft industry as 200,000v AT 200,000 amps. A 747 does pretty well at taking this kind of strike as there is a lot metal to go through. Even then, sometimes there are holes in the fuselage from direct hits. All electronics are well shielded which you're not going to do on a fiberglass boat. When lightning strikes, there is an initial attachment point to an "object" and there is an exit point on that "object". If you look at pix of aircraft strikes, it appears that it is being struck twice. Once up front and once in the rear ( or multiple). The aircraft (or boat) is simply part of the path. There is a video of a 747 getting hit out of Narita Japan. You can google it. The problem with using cables/wires to the water is that they will be blown off. It is not the magnitude of the current rather the magnetic forces (due to high current) that try to straighten the conductors out that blow them off. You can have the best connections, but if the conductors are a cirquitous path, they're not going to survive and current goes elsewhere.  

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