Roger Long wrote:

Thanks, this is very helpful. I'd planned on the flanges being
arranged so that the nut of the through bolt is sort of in the end of a
box. By extending the flange against the hull and making the top and
bottom edge flanges triangular, I could get in two or more bolts.
OK, Keep the box section but widen it vertically against the hull to
allow for two bolts. Add a rib down to the flange between the bolts.
After a trial fit has been done and all fixing bolts tightened to
conform it to the hull, take it out and braze or silver solder any joints.


My problem is that this all has to be done from one side so I can't put
bolts forward of the mast strut or main vertical plate.

Difficult. I presume there is a bulkhead in the way.
Can you get a strap round the front of the mast bolted to the copper
bracket either side sufficiently far out that it doesn't have sharp
bends in it? It wont have as good contact to the support post but should
help prevent flashover at the angle from the post to the bracket for
relatively little cost and difficulty of installation.

If I keep extending the bolt flange along the hull back to add
additional bolts, do I run into a situation of diminishing returns?
Yes. Two bolts a side is practical, three would be possible, more would
be of little benefit. Also the bolts should be as close as possible to
the main body of the flange and the same distance from it or the closest
will hog the current and the others be less effective.


It would be nice to simply duplicate the arrangement on the other side
but I have wires and plumbing running through that side of the bilge.
There is no reason why the other copper bracket cant have some big holes
in it for plumbing and other services, Just bolt braze or rivet a strap
of cross sectional area equivalent to the thickness times hole diameter
to both the top and bottom edges of the bracket.


I know I'll still have a lot of damage in event of a major strike but
I'd like to be figuring out my next move sitting aboard the boat than
swimming or sitting in a dinghy waiting for the next bolt. Most boats
that I have heard of being struck in this part of the world had only
electronics damage. even without good protection, so something like this
should heavily weight the odds in my favor.

Is there any advantage or downside to making this conductor out of
multiple laminations of 1/16" copper sheet?

Corrosion and getting even current sharing between the layers are
against you. Better to go thicker rather than thinner.

Dont loose sight of the fact that you *KNOW* you dont want any current
flowing down through the blocks of ballast in the keel and exploding the
possibly somewhat damp resin between them and blowing chunks of the skin
off. It also seems advisable to review your chain stowage. If its too
close to the foot of the support post, you will get side flashes out
through the hull via the chain.

I've looked over http://www.marinelightning.com/ and they dont seem to
say anything aboout the problem of a keel stepped mast (or a metal mast
support post) and the monohull installation link leads to a single
roughly annotated photo - not encouraging. Some good ideas and info
though especially for those of us with deck stepped masts without a
metal support post.