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On Sun, 09 Nov 2008 00:37:38 GMT, (Richard
Casady) wrote:

On Sat, 08 Nov 2008 16:33:21 -0500, Marty wrote:

Roger Long wrote:
This winter's major project is to add some serious lightning protection
to "Strider". What I have now is probably sufficient to increase the
odds of being alive to climb into the dinghy and watch the boat sink but
I'd prefer to sail home. It's not a subject that comes up often for a
designer of metal vessels so I've been look around the web and learned:

Do it like is done for tall buildings, strap a copper ribbon, 8" x 1/4"
up the length of your mast, one on each side. bond these at the base of
the mast to copper bus, 8" x 1/2", this bus is then bonded to a braided
copper cable approximately 6" in diameter and led to copper grid.
The grid should consist of an array of 1/2" diameter rod laid out to
form a square of no less 100' on each side, or any configuration giving
you an area of 10,000 sq. ft. The rods should be configured to form
squares of about one foot on each side, each junction should be bonded.
The main cable should be laid across at least 3/4 of the grid, or the
braid unraveled and broken into many smaller strands, each strand to be
bonded to the grid at intervals of two to five feet.

This will probably, but is not guaranteed to, protect your boat,
remember a lighting strike may exceed a million amperes, for a brief
time, but it does have a tendency of vaporizing anything smaller than I
have described.

Sounds like BS. My house barn and corn crib all had half inch or so
braided copper cable connecting 1/2 inch pointed rods. The ground rods
are presumed to be the standard ones the electrical places all sell.
They were struck hundreds of times, they were on top of a hill.

I heard it was 20 000 amps, at a million volts.

Casady

Does your barn have a 60 foot metal mast sticking up, supported by
multiple metal cables running down to various attachment points? Is it
floating on water, with no other tall objects around? How bi, and what
is the mass of the "earth" to which it is bonded?

The two situations are really not comparable.

Protecting a sailboat from lightning strikes is pretty much a fools
errand. Unless you have witnessed lightning strikes up close and
personal, you have no idea of the forces involved. It beats any
"fantasy explosions" or other special effects mayhem you have ever
seen in the movies.

A 1/2 inch copper wire would vaporize before it could carry the strike
anywhere. You aren't going to steer a lightning bolt, either. It has
no brains and will often jump a long distance, even if already
following what seems to be a path.

The best thing you can do for lightning protection on a sailboat is
anchor near other boats with taller masts than yours, and THAT is also
foolishness and completely useless. It's only benefit is a little
humor.

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