Posted by lance_ryley (lance_ryley@…>)
Here’s a response I got from Don Casey on the subject:
Dear Lance Ryley,
You recently submitted a question to BoatUS expert Don Casey: Do-It-
Yourself Guru. Our expert had a chance to review your question and has
provided an answer:
Your original question:
Hi Don,
I just finished your boat electrics book from cover to cover and am
about to start work, esp. on my shore system. I live on a Freedom 40
Cat Ketch with free-standing carbon masts, and wanted your take on
lightning and carbon fiber, and also the cone of protection as it
pertains to split-rig vessels.
Thanks,
Lance Ryley
Bright Star
Our expert’s answer:
Since carbon fiber is an indifferent conductor, some other conductor
is required to safely get a lightning strike to ground. The carbon
masts on Freedoms have a lightning rod at the truck connected to a #4
cable in the mast laminate. The lower end of the cable is connected to
a ground plate on the outside of the hull. If your Freedom is set up
this way, you and your crew should be protected from lightning strike.
If you do not have a conductor connected to ground, the mast will not
provide reliable protection.
The “cone of protection” scribes a circle at water level with a radius
approximately equal to the height above the water of the grounded
lightning rod. That means that cone associated with either mast should
include the entire boat. Having two masts does not lessen your
protection. Each functions individually—assuming both are grounded.
Lightning will prefer the shorter leap to the masthead.
If you do have the misfortune of a direct hit, your mast is likely to
suffer. You should have an ultrasonic and/or a bend test performed.
Repairing a lightning-damaged carbon spar is usually not cost-
effective. If the tests reveal damage, you will need a new spar.
— In freedomyachts2003@yahoogroups.com, “williedoylemom”
<williedoylemom@y…> wrote:
A friend told me that if lightening hits a carbon fiber mast it will
destroy the core. You won’t know if this has happened until some
stress is put on the mast and then it will just buckle. I’ve
researched this on Google and cannot confirm it. Does anyone know
if
something like this? Or is it just an urban myth. We are considering
buying a Freedom 35, looking at some here in Florida now. We’d like
to know if this is something we should watch out for. Thank you,
Faith