Bronze Winch on Aluminum Mast

[voxxmd]

Replacing a failed mast-mounted winch. Mast is aluminum (not painted, not anodized). The winch is a Barient 10 chrome-plated bronze unit, and the base w/mounting flange is bronze. Because of the dissimilar metals, should I coat the base with something or use some sort of gasket? Any suggestions?

TIA,
Michael

[djmarchand]

Butyl rubber sheet would be good. Tef-Gel would be OK.

David

[Jesse]

David has offered good advice, and there are other options like relocating the winch to the cabin roof where it can be accessed from the cockpit, eliminating a path for electrolysis.

[Blue Stocking]

The synthetic lids from Crisco, peanuts, and such ,make very good gaskets IMHO.

[Andrew Troup]

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.

The gasket 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 further compression, 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.

[David M]

No problem, as long as you bed it well where there is bronze to aluminum contact and that your mast is not submerged, where it would then become a battery with the ocean acting as the electrolyte.

I deal with disimilar metals on an aluminum boat all the time. If you stop the water and marine air from reaching where the disimilar metals make contact with bedding compound then you stop the electrolysis. There of course is the option of electrically isolating it with various types of electrical insulators.

I have had stainless steel thru-hull valves threaded onto threaded aluminum pipe nipples withut any corrosion for years. I did this by coating the insides where the aluminum makes contact with the stainless by epoxy coating the inside of the the nipples. No water contact at that point, no corrosion.

[Cheechako]

Been done many times, the good news is your mast is unpainted. I'd insulate as best as possible and call it good.

[SVAndante9]

We put a thin piece of marine grade starboard plastic between mast & winch. I think it'll last another 20 years!