Several years ago, while preparing an article on "Lightning Protection Systems"( Practical Sailor, December 1993), I interviewed one of the engineers responsible for preventing lightning damage to the U.S.'s largest power utility, the Tennessee Valley Authority, plus others at firms making lightning damage prevention systems for high-risk operations such as petroleum refineries and tank farms. The conclusions reached were fairly simple, and within a short time after the article was published, advertisements began to appear for devices called ion dissipators, like those previously offered only in high-tech industrial systems. These are stainless steel wire brushes, typically about two inches in diameter and about eight inches long. You can buy a similar brush for a few dollars from a supplier of dairy cleaning equipment; the ions probably can't tell the difference, but you will have to build your own mount.

In practical terms, it comes down to this: If I were a boater in Florida's "lightning alley", I'd make sure the boat was well grounded. One way to do this is make a grounding plate from 1-1/2" to 2" wide bare copper grounding strap, as long as can be fitted below the waterline, epoxied to the hull exterior. As an alternative, make a "buss bar" using 1-1/2" - 2" copper strip under the boat running from the base of the mast to the engine or, another alternative, several square feet of copper sheet epoxied to the hull, with a substantial grounding lug extending into the bilges directly below the main LPS cable (which, in turn, leads straight to the air terminal). If it were not feasible to run this cable - 4 AWG is a good conductor - straight down the masthead to the bilge, I'd make up a jumper cable long enough to reach from the overhead to the bilge, to be clipped in place when a storm threatened. This means that access must be provided to the cable, where it enters the cabin overhead, and to the ground lug with sturdy (bare!) connection points to which you can clamp the jumper. Do you think that this is too much trouble? Ask someone whose boat has been struck.

FACT: Lightning strikes are radio frequency (RF) events. It is true that the build-up of energy is a direct current (DC) phenomenon, and the current flowing during a strike is unidirectional, but as each spark starts and stops, a great deal of high

FACT: It is better to avoid being struck so you do not want to "attract" a strike to any part of your boat. The power of a direct strike is likely to heavily damage anything in its path and nearby electronics will suffer corollary damage from a side-effect of the strike, the magnetic pulse. Therefore, I suggest that the primary goal of an LPS must be to allow the accumulating "ground charge" (the buildup of energy in the earth or sea below a thunderstorm) to drain away at a low voltage level and to prevent the initiation of a strike. This is what the "ion discharge" or "dissipator" air terminals are designed to do. For these to be effective, however, they must be part of a well-designed system.

FACT: No LPS is any better than it worst component. Although the most obvious part of an LPS is the air terminal (or dissipator) mounted atop the rigging, it actually starts with the water beneath the boat. What is needed is the best possible ground so that the charge building up in the water can get to the air terminal. You can guarantee the best ground by having a bare metal hull.

Oh well, so much for the best. What's second best?

Second best is to have many square feet of metal wetted by the water. If this is still a problem, it is possible that connecting all underwater metal through-hull fittings to the LPS may be helpful, but you run the substantial risk of having a fitting blown apart in a strike, leaving a big hole in the hull of your boat.

To avoid becoming part of a side flash, you should understand the second purpose of the LPS; martyrdom (self-sacrifice).

When the LPS fails to prevent a strike, it must sacrifice itself in such a manner as to best prevent damage to the boat and its occupants. You encourage this vital role of the LPS by visualizing the path(s) that a lightning strike might take, then make the LPS conductor the one path that is as short, as straight and as low in resistance as possible. Then, during any lightning threat, you and your crew should stay as far away from this "favored" path as you can.

If you've done a good job on these basics, from ground plate to conductor to air terminal, and if you keep as far from the primary protection conductor as possible, then you've taken practical steps to guard against one of nature's mightiest forces.

Only one more suggestion: monitor weather reports and avoid being caught out in a thunderstorm!