[TowerTalk] Carbon fiber & lightning

[dennis o'connor]

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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