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Protect yourself, and your boat, in a thunderstorm

By Capt. GEORGE TUNISON - | Aug 20, 2021

Capt. George Tunison

When should a boat owner think about tossing a 1-foot-square of copper sheet material over the side?

What’s a “cone of protection,” an “air terminal” or “Franklin Rod”?

During a lightning storm, are you safer in an aluminum or fiberglass boat?

It takes less than 200 volts to fire a spark plug in your car’s engine. A lightning strike is capable of 100 million volt,s which is more than enough to turn you into what the 7-year-old neighbor boy calls, “a crispy critter”

After previously mentioning Florida’s summer afternoon lightning and the danger it poses to folks enjoying the outdoors, I received several emails concerning lightning protection for small boats, if is there is such a thing, and how does it work?

Large metal ships are struck quite frequently with little damage because the huge charge is quickly dissipated due to the large metal surface area of the hull in the water, grounding it.

An open boat like a runabout is the most dangerous to human life during lightning storms, since you are the highest point and most likely to get hit if the boat is struck. Odds are one in a thousand. Lightning also likes tall masted sailboats.

In a typical ungrounded fiberglass bay boat, there’s no metal hull or large ground to dissipate the charge or strike, or no way to efficiently direct the strike, so radio antennas, graphite lightning rods (fishing rods), towers, outboard engines, helm controls and you are all fair game for a hit in the lightning’s search for a path to ground.

So what’s the best way to NOT become a lightning victim while on the water during a bad storm?

The best way is to not be there in the first place. Before you plan your trip, consult a few trusted weather sites for an accurate forecast and always remember a forecast is an educated guess. Most already understand that living in the sub-tropics of Southwest Florida that the summer afternoons are often accompanied by violent storms, so getting out early and then returning early should be the plan.

If you’re already at sea and hear thunder or see lightning, remember that the sound of thunder travels roughly 1 mile per 5 seconds. Don’t wait around because you’re on a hot bite.

If you get caught in an open boat, anchor up, remove jewelry and get as low as possible in the hull.

Protect yourself, your boat, engine and sensitive electronics by installing a lightning protection system. It’s important to understand that lightning protection systems do not prevent lightning strikes. They may, in fact, increase the possibilities of the boat being struck. The purpose of lightning protection is to reduce the damage to the boat and the possibility of injuries or death to the passengers from a lightning strike by providing a cone of protection over the hull and by directing the strike safely to a ground source.

A boat protection system consists of three parts: an air terminal or Franklin Rod at the highest point on the boat to take the strike, and then a wire or conductor attached to it to provide a path for the charge down to the third component, the grounding plate which is permanently attached to the hull below the waterline. On small boats, a telescopic portable mast of the proper height would be erected, connected to the conductor wire, and then to a copper plate thrown in the water.

The air terminal or protective mast will generally divert a direct lightning strike within a cone-shaped radius two times the height of the mast, so the mast must be of sufficient height to place all parts of the boat within this cone-shaped zone of protection. Measure carefully to protect the whole boat.

Secondary items in your protection system would include surge protectors or isolators to protect radio, radars, engines and other sensitive equipment.

Capt. George Tunison is a Cape Coral resident fishing guide. You can contact him at 239-282-9434 or captgeorget3@aol.com.