Insulating the Mast from the Step

[Jim Fulton]

I had the mast on our 1975 Bristol 34 unstepped this year for some serious maintenance--rewiring, rebedding hardware, etc. The mast and step are in remarkably good condition. There is some minor corrosion on the bottom 1/4" of the mast, but not enough to worry about. The mast step is a stainless steel plate with four nearly-vertical tabs or ears that locate the mast. The tabs are about 1-1/2" high. My question is this: when I put it all back together, what is the best way to insulate the mast from the step to prevent further galvanic corrosion? I can't think of anything better than a heavy coat of Tef-Gel on all of the contact surfaces. There isn't room to put anything between them that is more than about 1/8" thick (and I can't think of anything that the weight of the rig wouldn't cut right through).

Jim Fulton

[Brion Toss]

Hello,
How about starting with a layer of UHMW tape, then slather Tef-Gel over that? It's true that the tape won't hold up in places, but then there's the Gel in reserve. Also make very sure that you have at least one generous weep hole, and of course that there's no stray current down there...
As for the minor corrosion now present, get that metal as smooth as practicable first thing, to provide less landing for corrosion.
Fair leads,
Brion Toss

[osteoderm]

Is this a keel-stepped mast? When we have these problems around here, they're usually in the form of an aluminium step "welded" into an aluminium mast heel, resting atop a corroded steel support under the cabin sole.
Before isolating, gelling, etc., we always seriously clean all the metal surfaces, even using a little muriatic acid to speed things along, finishing with a good round of punishment with a non-ferrous wire wheel; you really want to knock all the gunk out of the pits and see what you have to work with. Depending on the level of corrosion, by all means go ahead and get rough with the chipping hammer; better to expose a weakness now than later, during use!
After that, we use several coats of zinc-chromate primer on the aluminium, and Ospho followed by red oxide primer on steel. Stainless naturally benefits from close polishing and re-passivating. i think that solid surface prep prior to isolation attempts is key.

[Jim Fulton]

Thanks for the ideas. There's no difficulty stepping and unstepping the mast; as I said, there is realy very little corrosion compared to some of the horror stories I have heard. I have some .010" UHMW tape; I'll put some of that on the step. I have cleaned the corroded areas on the mast; I'll smooth them out and look into zinc chromate. I'll also polish and try to passivate the step.

Jim Fulton

[osteoderm]

"Zinc Chromate" isn't always sold under that name as such, but it's commonly used and available as primer for aluminium outboard/outdrive legs. Usually in a spray-can, it goes on as a lurid green-yellow wash that may require some well-applied overcoating to hide.