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Wilderness Medical Society - snowmass 2005 (Page 153)

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Wilderness Medical Society - snowmass 2005
grounded, metal structure, in which all of parts are bonded together and carry the
same electrical potential. Such a "cage" attracts and carries any lightning strike to
ground much like lightning rods on buildings. In other words, you need to provide an
unobstructed way for the lightning to dissipate its energy to ground (the water
surrounding you). Faraday himself risked his own life to prove this theory. The
additional benefit of a lightning protection system is that it tends to bleed off any
charge build-up in the
general vicinity, possibly averting
a lightning strike in
the first place.
So how does a lightning protection system work? In a boat, the "cage" is formed by
bonding together, with heavy conductors, the vessel's mast and all other major
metal masses. A marine electrician must tie in the engines, stoves, air conditioning
compressors, railings, arches etc. with a low resistance wire which would ultimately
provide a conductive path to ground (the water) usually via the engine and propeller
shaft, keel bolts, or better yet, a separate external ground plate at least 1 square
foot in dimension. It is important that you ensure that your crew fall within the
protection of the "cage," something not always feasible when the vessel is not built
of steel or aluminum. On fiberglass or wooden boats it is advantageous to have a
mast or other conductive metal protrusion extending well above the vessel, creating
what is known as a "cone" or zone of protection.
(I listed the above to be complete as you see this commonly
written, but note NO GOOD data to support the "cone of
It is generally accepted that this cone of protection extends 45 degrees, all around,
from the tip of the metal protrusion. This means that if the aluminum mast of the
average sailing vessel is properly bonded to the vessel's other major metal masses
and is given a direct, low-resistance conductive path to ground, the entire boat
should fall within the protected zone. If the vessel has a wooden or composite mast,
a marine electrician can achieve the same effect by installing a 6 to 12 inch metal
spike at the top and running a heavy conductor down the mast and as directly as
possible to ground, usually through the engine and propeller shaft.
Again, refer to the ABYC standards and have a professional marine electrician install
your lightning protection.
This is not a do-it-yourself project.
While on the water, stay alert. . .
Check NOAA Weather Radio for latest warnings and forecasts.
Watch for signs of approaching storms:
dark, threatening clouds that may foretell a squall or thunderstorm
a steady increase in wind or sea

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