Boat lightning strike damage: what to check after a strike and how surveyors write it up

Lightning is rare on a boat and expensive when it happens. BoatUS found about one boat in a thousand has a lightning claim each year, and the damage that matters most, at the waterline, is the damage nobody sees from the dock.

Who gets struck

From ten years of BoatUS claims:

By size, boats of 40 to 64 feet had 6 chances per 1,000 and boats of 26 to 39 feet 2.1. An earlier BoatUS analysis found Florida had 33 percent of all lightning claims, with 3.3 boats per thousand struck there. Along the Pacific coast it's about one in 10,000.

How a surveyor checks it

The hull first. BoatUS's claims department advises a short haul as soon as possible after a strike. The current can leave through a through-hull, or through the hull itself, and a gradual leak can go unnoticed until the boat sinks. Look at every through-hull and transducer for crazing, scorching and weeping. Boats on the hard often fare worse, BoatUS notes: the strike finds its way to the jackstands and can leave a visible track across the hull. In one claim, a properly bonded seacock sat on a plastic through-hull; the strike jumped across it, destroyed it and partly sank the boat.

The masthead. A damaged or missing VHF antenna is usually the first sign an unattended boat was struck.

Fuses and panels. Surveyor Dewey Ives, quoted by BoatUS, says more than a couple of blown fuses points to lightning.

Electronics. Test everything. BoatUS lists instruments, chargers, autopilots, refrigeration controls, battery selector switches, breakers, meters, alternators and lights among damaged gear.

GFCIs. Surveyors told BoatUS that shore power GFCIs are nearly always destroyed and easily overlooked: they may still pass power with the protection dead. Press the test button.

The compass. On a boat next to a struck one, BoatUS recorded a compass 50 degrees off that slowly returned over a few weeks.

What decides the grade

Water. Anything at or below the waterline is an A until it's repaired. Electronics and protective devices are B. A past strike with nothing found is a C, with a note to look at the through-hulls next time she's hauled.

What it costs

BoatUS: lightning claims are a small share of all claims, but in a decade of its files more than 75 percent were for less than 30 percent of the boat's insured value, and nearly all of those were for damaged electronics. Fire after a strike is rare.

Photos to take

Every through-hull from outside and inside, the masthead, any scorch or track marks on the hull, the panels and blown fuses. With Axsail, say which systems failed as you test them and they go on the finding.

Writing it up

Give the date of the strike if known, what was found at the waterline, then each system tested and its result. Keep damaged equipment for the insurer. BoatUS tells owners not to throw anything away until the insurer agrees.