Lead ballast bolts
I'm building an all wood schooner in southern Thailand. Shes about 22 meters on deck and will have a 3 ton cast lead ballast hung beneath a largish solid wood fin keel (all a very traditional "grand banks" schooner design). I hadn't expected this to be a problem, but silicon bronze (my first choice) bolts or rod stock are not to be found in this part of the world (or are they, anyone?). So, the external lead ballast under the deadwood still needs bolting on, and I'm torn between two options. The first one is to insulate stainless steel keel through bolts using machined plastic bushings (glass filled nylon or another non-compressive plastic). The second is where my question lies. What about copper? Electrolytic erosion being the obvious concern, is copper reasonably compatible, in this sense, with lead? Given, of course, adequate tensile strength for the copper bolts and enough of them, is this a good option (e.g. is the likelihood of electrolysis as great as with a pairing of ferrous and lead)?
Any help or fwd. ing is appreciated.
Kind Regards -
Couldn't you use galvanized steel bolts instead.
They have been used on a fair number of production boats with a fairly decent record. They are considerably stronger and cheaper than the copper bolts would be, if you could even find copper bolts.
If you're using stainless steel bolts, you'd be best off using 316 rather than 304 stainless as 304 stainless has some issues in a low-oxygen high-chloride ion situation that can cause premature failure.
Copper would be a dubious option. It might tend to elongate or bend under the load unless the bolts were absolutely huge. (Talk to a metallurgist, but this may be why you don't see many big copper bolts.) I'd also be concerned about the reaction copper might have with salty bilge water. Stainless has its issues, but would probably be better than copper. Another solution, à la Fatty Goodlander of CruisingWorld, would be to look online for some silicon bronze bolts of the right size from a reputable manufacturer and have them air shipped to you. Though it might be expensive, it would certainly be less than having the keel fall off somewhere near Sumatra, and a lot less exciting.
Think on this:
Copper and lead are used in batteries because of their effiency of conducting electricity. I would consult a metallurgist. I think 316 stainless would be a better choice.
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