1) I don't think Starboard is an appropriate backing plate due to the mentioned adhesion issues. You don't say whether the hull
is glass or metal, however, which would affect my answer. If glass, I think the best course is to encapsulate plywood
, and then epoxy
all that into place making the "pad" area about four times the area of the seacock base. Then, after drilling the hole slightly oversized, epoxy the hole shut in a manner very similar to how you do a hole in a cored deck
properly. Then, drill through the epoxy. Now both pad and hull
are isolated from the ocean by a "donut" of epoxy. Also do the same for mounting screws or bolts.
2) Yes, there is an issue with galvanism here, at least potentially, pun intended. The answer to bonding is "it depends". I recommend this book:
in order to fully understand the issues.
For instance, I have bronze seacocks on steel
threaded pipes below the waterline that I will be swapping out for Marelon, not because I love Marelon, but because only being in non-electrified freshwater has kept me from having problems with corrosion on a steel hull