What you should know about lightning and your sailboat
By Marlin Bree

"It was one of the few times on Superior I've really been scared." I was aboard my sloop Persistence, bobbing peacefully in beautiful Prince Arthur Marina in Thunder Bay, Ontario, listening to a veteran Canadian sailor. He was sharing a memory with me, the way sailors do, of a sailboat cruise he took on Lake Superior to Isle Royale. "I was out on the open waters," he continued, "and all of a sudden, all around me were lightning flashes, zapping the water. I thought I was going to be next. I was clearly the tallest thing around - and my mast the biggest lightning rod." I could sympathize with him. No question: He was in danger.

* * *

Lightning storm in Waukesha, WI.

Lightning is a serious problem. I recall seeing the results of a lightning strike on a 27-foot sloop in the harbor at Cornucopia, Wisconsin. A few inches above the boat's waterline was a fist-sized hole. The lightning had struck the aluminum mast, followed the mast down into the boat, and, then jumped from the hull into the water. Naturally, all the electronics were fried. No one had been aboard, but if they had, the damage might have been worse than just a hole in the boat and shot electronics.

* * *

Basically, lightning is a tremendous electrical charge that occurs in the atmosphere and it is attracted to the tallest nearby object. Sometimes this is a sailboat. The thought of hundreds of thousands of volts running wildly through a lonely boat out on the water is more likely than many boaters realize. In Florida, for example, the Florida Sea Grant estimated that lightning can be expected to hit from four to twenty percent of moored sailboats per year and that cruising sailboats typically get hit at least one time during their lifetimes. Worse, there is no way to protect against a strike. In fact, there is no sure-fire lightning protection. As I built my own 20-foot wooden sloop, Persistence, I contacted lightning experts who told me the only thing that you can do is ease the path of lightning through your boat. You can't stop it from hitting your boat, or shooting through your boat. The best you can hope for is to conduct the lightning strike through your boat in the path of least resistance - one that you have set up. It's called a grounding system. I began by getting a heavy copper plate and through-bolting that to the bottom of Persistence's keelson. This would provide my "ground." Inside the cabin, I secured braided copper wire especially made for a ground to my ground. The wire is about a half-inch in diameter, and, it leads on both sides alongside my wooden mast support to the top of the cabin. Here I fastened the copper wire to the stainless steel bolts holding my stainless steel mast tabernacle. Atop the cabin, in the tabernacle, my aluminum mast soars heavenward -- or at least as high as a 22-foot mast will allow. At one time, I had a special lightning rod atop my mast, but I discarded that. It stuck up several inches higher than my VHF antenna, and that was a few inches taller than the tri-color running light I also had up there. Lightning, I figured, wasn't going to be that particular: it'd just pick the nearest tall object and shoot down it until it discharged. The lightning rod, I thought, probably wouldn't conduct the lightning any better than the antenna, or, for that matter, my metal mast, which in reality was the biggest lightning rod of all. I now had a basic path for a lightning strike's electrical discharge. If the antenna attracted it, it would zap down the mast, flip inside the cabin via the copper cable, and discharge harmlessly through the copper ground into the water. I also made the assumption that if I got hit that I'd lose all electronics. I figured it'd be a small price to pay to keep my boat afloat. And myself, unfried. As it turned out, I had reason to be concerned. The Florida Sea Grant study said that boats in fresh water suffer more damage by lightning than boats in salt water. Why? Because fresh water is a worse conductor of lightning's electrical charges. On Persistence, I needed some kind of zone of protection through a bonding system. This was because the tremendous voltage that came down the mast wouldn't just conveniently leave by my pre-arranged grounding system. Actually, in an electrical strike, large voltages can develop between metal parts in the boat - for example around the cockpit where the skipper and crew are - and this is very dangerous. I began tying in all metal parts of the boat into my ground. The way I did this was by crawling into all spaces under the cockpit, cabin and foredeck and adding an extra nut and washer to the through-bolted metal parts, such as the engine mount, stainless steel lifeline stanchions, winches, genoa track, through-bolted cleats and heavy chain plates and shrouds. In turn, these were wired to my grounding plate. Basically, this smaller wire became a horizontal ring of protection to bleed off electrical energy.

Now I was all set. If I couldn't totally "protect" my sailboat from a lightning strike, at least I had some grounding and bonding protection. This would divert most of the initial discharge and drain voltage away as much as possible. Besides, lightning never strikes twice. Or does it? An internet story came to my attention from a boater in the Tampa Bay, Florida area, who got hit three times by lightning. He figures a part of his problem was that his mast, at 63 feet including the VHF antenna, was the tallest in the marina. But he added that his boat had the tallest mast only by a couple of inches, and, maybe that wasn't the only factor. He filed three claims for the three lightning strikes, two of which were direct hits, for having to replace all electronics. A third claim was for a near miss by lightning, but still had enough voltage to burn up many of his electronics. The insurance paid out a total of $73,000 for lightning damage, and then failed to renew his insurance policy.

Lightning factoids for sail boaters:

Beware of cockpits: Basically, the cockpit is the most dangerous place in a sailboat that is not bonded because of its metal parts. For example, during a lightning strike, large voltages could zap a skipper big time if he or she had one hand on a metal steering wheel and, for example, the metal engine controls or the lifelines.

On a foggy day on Lake Superior, Marlin Bree tries out the custom-built wheel aboard the wooden sloop, Orenda. The 45-foot vessel owned by Mike Keyser was anchored outside CPR Harbor, off Ontario's shores. Photo: Cam Reid)

Head for safety: When storm clouds gather, head for shore. The worst place to be is on the open water where you and your boat are the tallest lightning rods around.

Try a little radio: An old sailboater's trick is to turn on an AM (not FM) radio to listen for static. This will tell you if there's an electrical charge building around you. Small, cheap portable radios are best.

Go below: If you do see lightning zaps too close for comfort, go below, if you can. That gets you away from all that metal in the cockpit.

Stay away: If you do go below, stay away from the mast-to-keel area. That's the primary route of the lightning seeking a place to exit.

Don't go near the water: Avoid any connection between yourself and the water. Your body is a better conductor than air, and lightning will like you better than air as a better route. You become a human lightning rod.

Worst-case scenario boat: The worst boat to be in during a lightning strike is a small sailboat in fresh water. Even if the boat has a well-built protection and bonding system, "it is still an exceedingly hazardous situation," says the Florida Sea Grant. If there is no lightning protection, the situation is "life threatening." In both protected and unprotected sailboats, advises the Florida Sea Grant, the places aboard to avoid are directly beneath the mast or the boom. Stay with the boat. If you think of going overboard, if you are in an unprotected boat, "electrocution is highly probable if lightning strikes nearby." In fact, says the Sea Grant, "there is no safe place on an unprotected small sailboat and in a protected boat only places of relative safety."

* * *

If the lightning factoids seem a little hard to take, take heart at Sea Grant's additional advice: "There is one place that is more hazardous than a small unprotected sailboat, it's a small, unprotected boat without a mast. Every year there are multiple deaths of boaters in open boats caused by lightning strikes, but there are very few reports of sailors in sailboats killed by lightning." Zap! One never knows, does one?

Marlin Bree is a frequent contributor to Northern Breezes and is the author of four books about boating, including his latest, Wake of the Green Storm. (see His sailing adventures during Superior's "Perfect Storm" are included in a new nonfiction anthology from International Marine publishing, Treacherous Waters: Stories of Sailors in the Clutch of the Sea, garnered the publisher says, from "the best writing about sailing and the sea from the past 40 years."