It was hot and noisy in the cabin of Clearwater, a big reproduction Hudson River Sloop. We were tied to a pier on Iona Island, just downstream of the Hudson River Highlands, with a thunderstorm raging and everyone huddling below. I decided it would be more peaceful on deck, so I put on my foulies and went outside. I was standing next to the tiller when I heard a loud bang. My eyes shot to the top of the mast where I saw a small brown cloud and bits and pieces of antenna flying into the marsh. We had just been hit by lightning. And it was amazing. Not only was I still alive, but the deck was soaking wet and I hadn't felt the slightest tingle.

One might say that I was lucky, but the truth is that luck had nothing to do with it. Clearwater has a grounding system to protect it against lightning. Lightning systems can be simple or complex, depending on the boat, and are a safety feature many boaters can install themselves. The system on Clearwater was simple, but effective. The odds of being hit by lightning are pretty slim, but it's not a bet you want to lose.

THE BEST DEFENSETall objects present a target for lightning. On land, that may be a building. On water, it may be a mast.

Thunderstorms produce lightning when water within the storm cloud– liquid or solid–is set in motion by turbulence of the storm. The friction creates huge quantities of static electricity–as much as 30 million volts–and tall structures such as buildings and towers are the most vulnerable.

That means any boat--and particularly sailboats, with their tall masts–also present a raised object to target. Most boats don't get hit, but it does happen, as it did that night aboard Clearwater.

Your best defense is to find yourself inside a Faraday Cage, an enclosure formed by conductive material named for physicist Michael Faraday. If you're safely tucked inside such a cage, the electrical charge will follow the metal and avoid you. An automobile is one example of a Faraday cage, as is an all-steel boat.

A lightning rod connected to a ground will provide a "cone of protection" that carries downward at a 60-degree angle. Shown here are various configurations, and the lesson is obvious: the higher, the better.

Because most recreational boats are made of fiberglass, additional protections are required. You can simulate a Faraday Cage on any vessel by installing a raised, pointed conductor–a lightening rod–that touches a ground and creates a cone of protection around you.

MAKING IT WORK

Start by evaluating the system in place, if you have one, with a top-to-bottom inspection, and get a professional opinion if necessary. Do not assume that your boat is adequately protected.

I once bought a boat that the builder claimed had lightning protection. This "protection" consisted of thin wire loosely connecting a chain plate to a bronze thru-hull–not exactly an overbuilt system. I'm convinced that if the wire actually survived a lightning strike, it would have blown the thru-hull right out of the boat.

If your boat needs upgrades, you can again turn to a professional or make modifications yourself. So how do you safeguard your boat? First, find to the highest point. On a sailboat that's easy: it's the mast, or tallest mast in a divided rig. Mount a lightning rod–a pointed metal rod that extends up at least six inches–on the top.

This rod must then be connected to a ground. If you have an aluminum mast that is stepped to the keel, and your keel is made of iron or lead, the solution is simple: You will connect the bottom of the mast to the nearest keel bolt using a heavy-duty wire. If the mast is stepped on deck, you can run a wire via the most direct route to the bottom of the boat. If you don't have a metal keel, connect the wire to a metal plate measuring one square foot or larger attached to the bottom of the boat. A metal centerboard or large metal rudder would work, or you can use a copper plate. A ground plate used for a radio, though smaller, sometimes has ample surface area for this purpose. If your boat has a wooden mast, you can connect the lightning rod to one of the wire shrouds, then connect the shroud to a ground (that's the system aboard Clearwater and it obviously worked well). All wiring used for lightning grounds should be No. 8 gauge copper wire or the equivalent.GENE BJERKEHeavy duty wiring and lugs make a strong system.

On a powerboat, the highest point may well be the radio antenna. The American Boat and Yacht Council standards state: "A radio antenna may serve as a lightening protective mast provided it is equipped with transmitting type lightning arresters or means for grounding during electrical storms." If you cannot or do not want to use the antenna for lightning protection, you can install a lightning rod, properly connected to a ground, on the highest point of the boat. A line carried downward from this rod at a 60-degree angle will indicate which portion of the boat is protected. If the entire boat is not shielded, you may need to install additional rods.

With 30 million volts of electricity shooting down the system during a storm, large metal objects that rest within about six feet of the conductor may draw side flashes or currents. Such objects should be bonded into the system with heavy wire that is run along the shortest, most direct path. Make sure that all connections are mechanically strong, meaning lugs and other fasteners are made of heavy-duty, marine-grade material.

Before undertaking a project, you may want to read up. There are several books and web sites that proffer advice, but one solid source is Nigel Calder's Boatowner's Mechanical & Electrical Manual.