Hi,
I'm a newbie, just going over the last month's threads and ran across this:
Jim Jarvis
Fri Mar 18 21:53:16 EST 2005
Got a peripheral question, which relates to the
lightning thread. Would be interested in the groups
thoughts.
Been considering two sailboats. One has a traditional guyed
aluminum mast, grounded in a typical fashion...inadequately.
THAT, I can fix.
The other has a freestanding carbon fiber mast. No way to
ground it. Conductivity unknown, but I assume somewhat resistive.
Which is safer? And if I put an antenna (or lightning rod) at the masthead,
does it get worse, or better?
n2ea
jimjarvis at ieee.org
There was an article on conductivity of carbon fiber, especially pertaining
to RF grounds, in QEX last year. The "take home point" is that without
specific information on how it's made, you can't say much about carbon
fiber. It is somewhat conductive, but to make a good ground plane, you
need to add something to the mix to make it more conductive.
If nothing has been done to the CF mast to make it more conductive, it will
explode when hit by lightning. I have seen pictures of homebuilt CF
aircraft that have been hit. Smoking holes in the airframe can ruin your
day.
On the positive side, surely anyone who knows about building CF for
sailboats must know that they need it to be conductive, right? You could
run a long cable ground down to a water contact point, cable that's about
the diameter of your thumb.
As for the last question, do lightning arrestors prevent strikes, I've seen
so many arguments both ways, I'm not convinced. The big power poles around
here (the lightning capital of the US) all have what look like 1 foot
diameter wirebrush balls on their ends, that are supposed to cause corona
to burn off charge and prevent a hit. I guess the power engineers believe
they reduce the number of strikes.
73,
Bob
W4ATM
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