Thunder Struck: Protecting your Boat from Lightning Strikes

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 The best way to prevent lightning damage is not getting hit in the first place

The best way to prevent lightning damage is not getting hit in the first place

Few things strike an uneasy feeling into a sailor’s heart like the sight of darkening storm clouds looming on the horizon, the rumble of thunder and the flash of lightning. Whether you’re watching a storm roll in from the cockpit, revving the engine to head for cover or waiting for the inevitable on the open ocean, the danger of your vessel being struck by lightning is real, and every sailor should take steps to protect their boat against serious damage should a strike take place.

 The chance you have of being struck by lightning depends greatly on where you do your sailing

The chance you have of being struck by lightning depends greatly on where you do your sailing

The rarity of lightning strikes seems to make the idea of “it’s not going to happen to me” fairly pervasive in certain parts of the boating world. When I asked Ewen Thompson, president of Marine Lightning Protection Inc., a company at the forefront of developing ways to protect boats and onboard electronics from lightning damage, what the most common mistake sailors make in regard to lightning protection, his answer was quite simple. “Oh, that’s easy,” he said. “The most common mistake is to do nothing.” Also, protecting against lightning damage is hard, and dealing with the electricity from lightning is very complex. “People are generally unprepared. The physics of the situation and the concepts applied are extremely difficult. Add to that the fact that the typical boat on the water is jam-packed with electronics, and it further complicates the situation.”

The chance you have of being struck by lightning depends greatly on where you do your sailing. According to meteorological measurement company Vaisala’s National Lightning Detection Network, if you sail on the West Coast the odds of getting struck by lightning are pretty low. However if you’re sailing on the Gulf Coast or along the East Coast (Florida is the worst) the odds go up significantly. In addition, the outcome will vary according to whether you are in fresh or salt water. “We found that if a boat was struck in fresh water the damage to the hull was much greater than if it was struck in salt water,” Thompson said. “Its possible that in salt water an immersed grounding plate beneath the waterline might be effective, however when it is in fresh water it is clearly not.”

This diagram shows how Thompson’s system might be used to run electricity from the mast to the waterline via internal wires and through-hull electrodes

This diagram shows how Thompson’s system might be used to run electricity from the mast to the waterline via internal wires and through-hull electrodes

So how do you go about protecting your boat? The goal, put very simply, is to guide the electricity from the lightning bolt down the mast, along the deck, and down to the water as quickly and simply as possible. “The first thing you look at is the mast,” says Thompson. “We start off by inserting a lightning rod right in the middle of the masthead and run a cable down the mast. We want to get the lightning cable out way before it hits the keel, because we need to connect the conductor to the outside of the boat down to the grounding conductors that are on the waterline.” It is important to get the lightning out to the water because the charges that neutralize the lightning sit on the water’s surface. By running a lightning rod from the top of the mast down to the deck and out to the ground charges, you guide the electricity as it flows from the sky to the water and help protect the boat and those onboard from being injured. “The grounding system is designed to protect the hull of the boat and the occupants of the boat,” Thompson said.
However, the biggest problem isn’t protecting the boat and those onboard, it is protecting the electronics. Now more than ever boats are turning into floating Radio Shacks, with electronic chartplotters, VHF radios, depthsounders and all sorts of other electrical equipment onboard. “The problem is that if you put a grounding system on a boat that is the best we can provide, you still can’t expect that it will protect the electronics,” says Thompson. “In order to protect electronics, there could be an over-voltage anywhere that could fry the electronics. And now with network bus systems each pathway is a pathway for an over-voltage to form and blow up every piece of electronics.”
One thing that Thompson and his team have been working on to prevent this is working with surge protection. “Anything on the mast should be considered a high-voltage generator, and the voltage should be intercepted right at the base of the mast” Thompson says. “The idea is to cut off the voltage before it reaches the electronics themselves—at the base of the mast I have a single point ground, if we can reference everything to the same local ground and eliminate potential differences then that’s the way to protect electronics.”

So while there is certainly a chance that it will never happen to you, if you sail in an area where lightning storms are commonplace, setting up your boat to help prevent damage to those onboard and your electronic system is something you should definitely consider. The odds of it happening may be slim, but the damage to your boat might be anything but. Sure, lightning might never strike the same place twice, but if that place happens to be your boat, then once might just be enough.

Caution: High Voltage

While protecting your boat against lightning strikes is advisable to cruisers, especially those that sail in areas that are prone to lightning strikes, the best way to avoid damage from lightning is to avoid lightning altogether. One tool that can help coastal sailors combat a run-in with lightning is Sirius XM Satellite Weather ( No matter what package you choose—Marine Inland ($12.99/month), Marine Coastal ($29.99/month) or Marine Offshore ($54.99/month)—all of them offer near real-time tracking of cloud-to-cloud and cloud-to-ground lightning strikes, giving you the information you need to (hopefully) get out of the way before the strikes begin.



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