[TowerTalk] Carbon fiber & lightning
dennis o'connor
k8do at mailblocks.com
Sat Mar 19 07:28:42 EST 2005
Jim,
Carbon fiber structures are conductive at lightning voltage
potentials... Unfortunately, due to their inherently being a large
carbon resistor they do not do well trying pass large amounts of
current, heat up catastrophically, and basically explode - the old,
quarter watt resistor across the output of your 2KW amp, routine...
This has been a concern in the 'glass airplane' arena... To become a
certified airframe by the FAA a carbon fiber / fliberglass airframe has
to have a conductive metal mesh on the exterior, just under the gel
coat... Now, lots of experimental aircraft are flying without the
conductive skin, but they are not certified production airframes...
Now, having taken the long route to your question, I would prefer the
metal mast over the carbon for that reason... A PROPERLY grounded metal
mast (99% are not properly grounded, especially the wire from the mast
to the ground plate on the keel, and the ground plate itself) will take
a major strike without damage... The carbon mast is unlikely to
survive... Yes, running two strips of wide, copper tape up the mast,
one on each side, may permit it to survive - may - OTOH, if you
consider the mast expendable and if you like the unguyed (Is this a
Freedom?) mast, then go with the carbon mast and assume the boat will
be lucky...
The more likely scenario with the carbon mast, is that the current will
jump from the mast to the hull plumbing, blow off a thru-hull fitting
getting out to the sea, and the boat will sink...
denny
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