wrote:
Additional photos of the rebuild and refit project are now at:

http://www.pbase.com/gould/extreme_makeover

Things are beginning to go back together rapidly. Bow thruster
scheduled to go in next week.
With any luck will be launching in two weekends.

WOW awesome job Chuck. I am deliberately NOT going to show
my wife your pictures, hope you understand


There will be a new aluminum mast and boom installed. I suppose the
yard has this all figured out, but just in case,........

1) The painted aluminum mast will be stepped into a bronze fitting.
With dissimilar metals in contact there is a potential for
electrolysis. Being a stinkpotter and therefore relatively
inexperienced with masts, what precautions, if any, should one take?


A sheet of rubber gasket should be just fine, shape to fit
between mast butt & step. Another option is to paint the
mast butt with that liquid plastic tool handle coating (one
brand is named "Dip-It" commonly sold in hardware stores).


2) The old wooden mast wasn't much of a lightning hazard, but the new
mast would serve as an excellent conductor in the event of a lightning
strike. Ideas for grounding? Is it important to ground it?


Personally, I wouldn't worry about it. It may be more
effective to put a static dissipator brush on the tip and
leave it ungrounded. A lightning ground would be difficult
to install since it not only has to be thich cable, but also
relatively straight and on your boat it would have to come
down right thru the aft cabin. A minimum lighting ground
(think in terms of millions of volts) would be a 4" wide
braided cable with no turn of less than 8" radius.


RCE wrote:

This is a good question and I've heard a couple of theories. The first is
that a metal mast should be bonded to the boat's bonding plate to discharge
a lightning hit. The problem, according to some people, is that a direct
hit could carry so much current that it literally can blow the bonding plate
apart, resulting in a pretty big hole in the hull.


That's not a good idea IMHO. The bonding system will not
handle anywhere near the current of a lightning strike and
will only result in scattering the damage all thru the boat.
It will also result in more stray charges in the bonding
system which may cause other long-term problems even if
lightning never strikes.


The alternative is to not bond the mast. In these cases, mucho electronics
that may be mounted on it may be blow, and I've witnessed this on a couple
of sailboats that were hit.

My guess .... and it's only a guess ... is that the metal mast should not be
bonded so well that it can carry large amounts of current. A small diameter
wire that keeps the mast at ground, but would melt quickly in a direct
lightning hit would be my choice.
Again ... just my guess and opinion.


Sort of like a fuse? Not to be argumentative but the problem
with this idea is that the energy *will* go somewhere. It's
like you've invited this billion volt beast on your boat and
then tried to shut a flimsy hatch in his face. A mast should
either be ungrounded (and with a short mast like a
trawler's, this is not that big a risk) or well enough
grounded to take a hit. Either way the electronics connected
to it will be fried, that's a given. But a well grounded
mast will not damage other parts of the boat.

Lightning can do all kinds of funny stuff, from burning
holes thru the hull to melting ropes to setting wood
paneling on fire. I've know it to burn up alternators via
the boat's ground system. Some friends of ours just had
their sailboat hit by lightning and it fried all their
electronics and put what looked like cigarette burn holes in
their sails.

Fair Skies
Doug King