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The Big Hit Page 2

The Big Hit — Maintenance April 2001
The Big Hit
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Another bit of erroneous folklore is the notion that the presence of a lightning-protection system onboard a vessel actually increases the chance of a lightning strike. Nonsense, says Dr. Ewen Thomson, lightning expert and associate professor of electrical engineering at the University of Florida. Reports from lightning-strike survivors and marine surveyors who specialize in lightning-related marine damage indicate that a proper lightning-protection system with surge suppressors for electronics has only one effect: the prevention or at least reduction of all kinds of electrical damage, from exploded through-hull fittings to holes blasted through a hull. “A lightning-protection system is designed to safely conduct lightning current to ground, not attract it in any way,” emphasizes Thomson. “A proper system simply does not increase the probability of a strike at all.”

But what should such a system consist of? Organizations like the American Boat and Yacht Council (ABYC) and the National Fire Protection Association offer fairly similar recommendations. The basic system starts with a vertical conductor or “air terminal” mounted as high above the deck as possible. Ideally the tip of this terminal creates a virtual “cone of protection” with a 90-degree apex and sides that extend down around the entire boat. I say virtual because the cone simply delineates an area in which a strike is statistically less likely to occur, thanks mostly to the properties and elevation of the air terminal. While a single air terminal works best for single-mast sailboats, a catenary strung from one apex to another works better for those with multiple masts and for powerboats and motoryachts. The three other components of a basic system are a ground plate, usually a foot-square hunk of copper, monel, or naval bronze affixed to the outside of the hull bottom directly below the air terminal; a main conductor, typically of copper wire, that runs as directly as possible between the air terminal and the ground plate; and a bonding system that ties together all major metal components onboard and, depending on size and other characteristics, connects them either to the main conductor or directly to the ground plate itself.

Although this simple system is fairly complete, there are addendums specific to particular kinds of boats, which are too numerous to list here. But since some reflect a slightly different take on lightning protection than is commonly met with these days, here are two especially engaging ones, both excerpted from the ABYC’s E-4 Lightning Protection standard, available in its entirety from the ABYC for $35. The first involves the grounding plate. ABYC suggests that a longer grounding strip, approximately one inch wide and 12 feet long, may do a better job of dissipating electrical charges than one with more equal sides, primarily because it offers nearly three times the exposed edge area, and large edge areas seem to dissipate electricity more efficiently. Limited testing and data collected to date seem to support the conclusion, says ABYC vice president and technical director Tom Hale. The second detail of the E-4 standard, and one that’s fairly new, is a change in recommended wire size for the main conductor. Where #8 copper was previously recommended, heavier #4 is now preferred, the rationale being that #8 could overheat and vaporize like a welding rod.

Undeniably, the promulgation of standards is a good thing, although one hang-up continues to be bothersome: Because lightning protection standards are voluntary, systems are not nearly as common on boats as some safety-at-sea literature would indicate. The experts are divided on the reason for this. Some, like ABYC’s Hale, contend that the litigious nature of American society scares off builders. Since damage from most strikes is possible even onboard properly protected boats, they worry about being held liable. Other experts, like the University of Florida’s Thomson, maintain that cost is the problem, although Hatteras Yachts, one of the few builders currently offering lightning-protection systems as standard equipment on production powerboats, says the man-hours and materials entailed amount to less than $500. Thomson’s take on legalities, incidentally, is totally opposite of Hale’s. He contends that the failure of a manufacturer to address lightning safety where clear, though voluntary, standards exist is likely to generate, not prevent, lawsuits.

In any case, it’s a hard fact: Generally speaking, if you want a protection system on your boat, you’re probably going to bone up on the standard and install it yourself. Or else hire an ABYC-certified marine electrician.

American Boat & Yacht Council Phone: (410) 956-1050. Fax: (410) 956-2737. www.abycinc.org.
National Fire Protection Association Phone: (617) 770-3000. Fax: (617) 770-0700.


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This article originally appeared in the May 2003 issue of Power & Motoryacht magazine.

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