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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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