A lightning strike in Departure Bay off Nanaimo, British Columbia.

The lightning strike that recently hit a boat from Seattle while its owners were cruising in Costa Rica wasn’t all that unusual, experts say.

Even worse: they say there’s still no consensus on whether it’s possible to effectively protect vessels from lightning.

Bella Star, a 33-foot Hans Christian sailboat, was struck by lightning in early June while anchored out in Playas del Coco, a popular tourist destination. Owners Aaron and Nicole Maraschky, who left Seattle in April 2011 to go cruising, were onshore at the time and not injured. But the strike destroyed almost all the electrical equipment on their boat, causing at least $20,000 worth of damage.

While lightning strikes are unusual in the Pacific Northwest, boaters cruising in other parts of the U.S. or in foreign countries have more reason to worry.

Steve D’Antonio, a marine systems expert and journalist based in Virginia, said during his 11 years of managing a boatyard on Chesapeake Bay, he repaired many vessels damaged by lightning strikes — including a sailboat that was hauled out and repaired, only to be put back in the water and struck again while waiting to be picked up.

“So lightning does strike twice in the same place,” he said.

According to BoatUS, the odds of your boat being struck by lightning in U.S. waters are only about 1.2 in 1,000. Florida has the highest number of claims for boats hit by lightning between 2000 and 2005, followed by the Chesapeake Bay area.

Not surprisingly, the majority of lightning strikes are to sailboats, at a rate of 4 per 1,000, and multihulls are hit more than twice as often (9.1 per 1,000) as monohulls, according to insurance claims data from Boat USPowerboats get struck at a rate of 5 per 1,000, with trawlers being hit the most often.

Lightning causes electrical current to flow through any conductor it passes over, and a strong enough strike can cause current to be induced or flow aboard vessels even without hitting them directly. Electrical gear, from batteries to radar and chart plotters, is most commonly affected, but occasionally lightning makes a beeline exit through a boat’s hull and blows holes through fiberglass.

In extreme cases, D’Antonio said, lightning can cause a transducer to blow out of the hull and sink a boat.

“I’ve had cases of boats being struck at the dock and sinking as a result of a damaged transducer” he said.

So what’s a prudent boat owner to do, besides avoiding all lightning-prone areas? It depends who you ask. (BoatUS offers some tips here for avoiding lightning strikes.)

Some, including well-known marine systems expert Nigel Calder, recommend creating a “zone of protection” by installing a copper or aluminum rod that reaches at least six inches above the highest point on the boat and grounding it to a copper plane situated underwater, preferably directly below the mast.

This diagram, courtesy of Nigel Calder, shows the elements of a zone of protection on a sailboat.

An aluminum mast can effectively serve as the conductor between the rod and the ground plane, Calder said, but a carbon mast is not sufficiently conductive, nor is a wood mast. A separate copper conductor is needed for both, he said.

And the conductor needs to provide as straight and direct a path as possible to the ground plane. Wires should not be run horizontally or make sharp turns (“gentle sweeps” are better, D’Antonio said), since electrical current from a strike will want to exit the wire at those points.

The hull on metal boats can act as the ground plane, Calder said, but boats with non-metal hulls need at least one square foot of immersed metal if they’re in saltwater, and considerably more in freshwater, ideally located directly beneath the mast.

If the protection zone works as intended, a lightning strike would pass through the boat without blowing holes in it. But Calder notes that the boat’s electronics may still get fried, since the forces in a major lightning strike are so powerful that nothing is guaranteed to protect the vessel.

D’Antonio is skeptical about the efficacy of zones of protection, as well as about the few products on the market aimed at protecting boats from lightning. The best protection, he said, is a good bonding system that follows American Boat and Yacht Council (ABYC) guidelines and a substantial underwater metal contact area.

He recommends placing a long, narrow strip (versus a square) of 1/4-inch copper on the exterior of the boat’s hull. The edges of the metal plate are what dissipate the energy of a lightning strike, he said, so the longer the edge surface it has, the better. The edges should be left sharp, he said, with the exception of the leading edge, which can be chamfered, or beveled.

“The lighting dissipation products that are out there are probably inadequate on their own,” D’Antonio said. “What you can be certain about is that without a bonding system, the likelihood of damage is great, in my experience.”

D’Antonio cautioned that while the ABYC guidelines can help mitigate the impact of a lightning strike, a boat’s grounding system must be regularly inspected. He recommends having an ABYC-certified marine electrician do an inspection at least once a year to look for corrosion and loose connections.

“It’s not an install-and-forget kind of system,” he said. “In my experience, the greatest challenging with a bonding system is maintaining it.”

If a boat is struck by lightning, D’Antonio said, it should be hauled out and thoroughly inspected. That means unstepping the mast to see if the wiring inside it or the base is damaged, inspecting the windlass, checking thru-hulls and inspecting running gear.

Since anchor chain is often a path of departure for lightning aboard anchored vessels, he said, the chain should be removed and the anchor locker and the surrounding hull area carefully inspected.

Ultimately, D’Antonio said, when it comes to lightning there are no guarantees or even reliable steps to avoid damage.

“I’m skeptical of anyone who says they’ve got it figured out,” he said. “I don’t think there are any solid answers about lightning. There are just theories.”

About Deborah Bach

Deborah Bach is the editor and co-founder of Three Sheets Northwest. She is an avid sailor and longtime professional journalist. You can find Deborah aboard her Passport 40, Meridian, with her husband Marty and their cat Lily.

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