Cruiser?

Sailboat? The 'standard' mast is a lightning rod. No arguements,
if you are gonna get hit, that's where it will be, or the
shrouds, which should conduct at the masthead, and not at the
chain plates. One should not encourage lightning to traverse thin
wires holding up the mast.

A bipod mast system is probably best for this purpose, but may
not be so good for sailing. A heavy flat copper conductor,
outboard, from gunnel bipod mast tabernacles to the keel or sea
may be a good idea.

Fixed keel? My cast iron keels are the grounded elements
underwater. I expect lightning would boil off some antifouling
paint. Paint is an insulator, thin, easily arced across by
lightning. That would be the best place to take heat damage.

Heavy conducting king post? Or very heavy wire straight run
connecting mast base to keel bolt. If the wire is smaller than
the keel bolt, the wire will explode before the keel bolt does,
according to ohm's law. The bedding compound at the keel / bolt
interface seems to have been where the bolt found ground. I have
external keel bolts holding the keel flanges to the hull. I have
a bilge keeler, two shallow keels side by side. Actually, I
expected the crimped wire terminal ends to be the victims at
failure. Survivors will still be afloat.

Oversized keel bolts? The bigger the better, for resistive /
conductive purposes.

Just my thoughts, backed by my experience and observations. I
have an old mast hanging in the trees in my back yard with 25
holes eaten into it by one multi strike wowser of a lightning
strike while moored unattended at the dock. We suffered no other
damage. The VHF masthead AE and the radio were untouched. The 4
bolts securing the tabernacle to the top of the king post pierce
the overhead in the cabin, and were not damaged or overheated by
the strike. Most of the heat damage occurred at the places where
the arc contacted the aluminium mast, all 25 holes in a neat
dotted line down one side from the masthead to the spreaders
about 8" apart, all along a line of similar curvature on the
surface of the mast, not the most severely curved part. I think
the geometery of the curvature must have somehow been attractive
to the lightning. The bigger holes were nearer the top. The
bedding compound in the keel bolt hole in the hull used to ground
the mast appeared to have suffered some heat damage, possibly
boiled trapped contaminated moisture, and suffered a very slow
drip leak until resealed ashore by the insurance paid repair guy.

Knowing what I know now, and desiring to minimize damage, I would
use the same system I have now, and accept that 1/2" holes in the
mast where the arc chewed it up is better than a cabin full of
people with boiled copper vapour burns and possibly eye injuries,
which might happen with a ground wire of just the wrong
undersize.

Keep all electrical system wiring away from lightning ground
systems. The electrical system aboard does not need a ground to
the sea, including radio antennae, in my opinion. Galvanic
corrosion is enabled mainly by grounding systems not well thought
out. Insulated drive shaft couplings are a good idea, IMHO. A
small zink on the prop shaft would protect the shaft and prop, if
of dis-similar metals. Through hulls should be insulated from the
sea with paint or wax if neccessary. Dynaplates are not of any
use whatsoever. You can't paint them, they oxidize quickly
underwater, insulating themselves, they accomplish nothing, and
soon acquire hitch hikers. I admit, there is one on my boat, and
it's been antifouled, and not removed because it is the common
D.C. ground aboard almost under the engine, which I am presently
loath to rewire and patch the hole, as it doesn't need it, yet.
My ohm meter indicated it is an open circuit (no connection) to
the sea.

The distribution of heat generated by a lightning strike can be
controlled by proper distribution of resistive components in the
protection system, provided that God is not steering the
lightning bolt manually, right between the shrouds and into your
neck hole. The thinnest metal (in the mast) is what took the
brunt. As it should be.

A system of ropes on the tiller enables one to steer from below
even in a hailstorm. Have you ever sailed in a hailstorm? I
have. Not fun.

An insulated (wooden) mast would need a lightning ground
conductor attached to it. Unprotected trees hit by lightning
explode. Don't want that to happen to my mast.

Terry K

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I havent' been following this thread so the following may already have
been posted, but I was reading an old copy of "Royce's" which says on a
rig with aluminum mast and stainless steel rigging the ground must be
connected to the mast not the rigging (eg chainplate) because stainless
steel is a very poor conductor of electicity compared to aluminum. If hit
the charge will travel down the mast, not the shrouds. The book recommends
a copper ground from the mast to a copper plate attached to the exterior of
the hull below the waterline.
--
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