[TowerTalk] Carbon fiber & lightning

[Bob Lombardi]

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