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Mark Venture wrote:
>
> I pass along the following comments from Telltales Magazine August 1999
> page 22. The article entitled Lightening was written by Larry Crouch who
> is currently the repair yard superintendent at Seabrook Shipyard.
>
> The American Boat and Yacht Council (ABYC) suggest that a "zone of
> protection" may be formed around a boat by providing a direct path to
> ground form a lightening rod attached to the vessel's highest point.
> ABYC defines a "zone of protection" as "an essentially cone-shaped space
> below a grounded air terminal, mast or overhead ground wire, wherein the
> risk of a direct lightening strike is substantially reduced."
The zone of protection is 60 degree cone. This is true on land or sea.
What it does is protect something beneath it from a direct hit. When
you take a hit current flows through every conductor and everything,
except a perfect vacuum is a conductor, aluminum, steel, fiberglass,
your body, etc. Granted most of it flows through the path of least
resistance, but some of it goes through everything. Kirchoff's law
applies. The trick is to provide the best possible conductor away from
those things you keep near and dear, like your bod and the electronics.
Ideally, the mast is made of copper or gold and goes straight through
the boat to the keel, which is made of copper or gold. Anything you can
do to approximate that is desirable. Least desirable is having a wooden
mast (unprotected) or an aluminum one that is mounted on the top of the
cabin. Grounding the mast directly through the cabin is by far the best
idea. A 90 degree bend to lightening amounts to the same thing as a 90
turn to a dragster. It won't be used. If a majority of the lightning
is shunted through your rigging, you've probably just used up the most
expensive fuse you have. 8) A few million amps through 1/8 " stainless
will most likely disintegrate it.
I'm a firm believer in those funny looking brushes that they use to
dissipate lightning. They really do help, IMHO.
Jim.
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