Remember that you also have to insulate the fasteners, preferably from the mast
, but failing that, from the bronze winch base. Better still, from both.
If electrical current
can flow by any metallic path between dissimilar metals, where those metal might at times be linked by an electrolyte (eg a trail of damp salt
residue) there is the potential (inadvertent pun !) for the less noble one to be attacked by the more noble one.
for a winch needs to be quite low in resilience. I'm not sure butyl rubber is ideal from this standpoint, although if it's thin it could well be OK.
The problem is that a winch experiences major tilting loads, and consequently the bolts holding it down must be done up tight.
It's not possible to get bolts properly tight on items which are bedded on something excessively resilient; over time and with flucuating loads, the resilient material will permit
, which will leave the bolt less than fully tight.
There are no absolutes here: of course all materials are resilient (wood is a great example, being considerably more resilient than metals), and winches can be bolted to wooden decks without the bolts necessarily
coming loose ... but each case has to be taken on its own merits. A more rigid gasket material avoids the problem entirely.
Another durable option (some plastics used for containers eventually become brittle) is mylar in a heavy grade. It's easy to mark out hole positions on it, because it's transparent.