Corrosion - Stainless touching Aluminum spars

[hard-a-ground]

Hi all,

Figured folks here would have ideas to help me. I am refitting my Norseman 400 monohull (6 months owner now) - I noticed the stainless fittings on both boom and mast are causing corrosion in the aluminum.

Any ideas for how to work this problem?
Zinc anodes on both spars?
Rubber seal between the stainless and aluminum?

Looking for an approach to stop this process.

cheers,
Frank.

[noelex 77]

The most common techniques are applying products such as Duralac or Tefgel. The other alternative is to try and isolate the dissimilar metals as much as possible with plastic spacers.

These two methods can be used together.

Rubber is not ideal because of the carbon content. Often modern "rubber" products have little or no carbon but it difficult to be sure.

Anodes will not work on a mast.

[Cheechako]

I like Lanolin or Lan O Cote. It seemed to work very well on the spar /screws. Put it on thick, screw it in, remove the stuff that squeezes out. SS screws done with this will come right out after a couple years of salt spray soaking. That tells me they are isolated well.

[roverhi]

Have used vinyl dodger window material and electrical tape as insulators. Could also try using caulk behind the fittings, butyl comes to mind but any caulk with fasteners only loosely fastened till it has a chance to set up and then snugged up should also provide insolation. Think lanolin or such would eventually wash out and not do the job flat against the mast.

[atoll]

Originally Posted by hard-a-ground

Hi all,

Figured folks here would have ideas to help me. I am refitting my Norseman 400 monohull (6 months owner now) - I noticed the stainless fittings on both boom and mast are causing corrosion in the aluminum.

Any ideas for how to work this problem?
Zinc anodes on both spars?
Rubber seal between the stainless and aluminum?

Looking for an approach to stop this process.

cheers,
Frank.

any industrial nut and bolt supplier will have nylon washers,and nylon insert washers.
most also can supply nylon in sheet form.

insert washers are used by drilling an over- sized hole and pushing the insert washer into the hole then bolting on top with a conventional washer,this totally isolates the aluminium that is being bolted from the bolt.
the profile of an insert washer is _l l_

nylon washers should be placed in contact with alu surface,then a conventional washer on top before bolting through

equipment should be mounted on a full size nylon backing plate in contact with alu surface, nylon sheet material comes in many different thicknesses and is easily cut or drilled,can be routered as well.

failing that 2 liter polycarbonate softdrink bottle plastic makes effective isolation material and easily cut out to make a gasket

[markwesti]

Originally my mast and spars were isolated pretty well with PVC plumbers tape (like where a fitting or plate) was mounted . Those areas are still good even after almost 40 yrs' . Also 1+ on Tef Gel and stuff like it . One thing I did though was to replace non structural things like lights with brass screws and Tef Gel . Brass hates Alum. a lot less than SS .

[Cheechako]

Originally Posted by roverhi

Have used vinyl dodger window material and electrical tape as insulators. Could also try using caulk behind the fittings, butyl comes to mind but any caulk with fasteners only loosely fastened till it has a chance to set up and then snugged up should also provide insolation. Think lanolin or such would eventually wash out and not do the job flat against the mast.

Lanolin doesnt wash. It does get brittle over time though when exposed to sun. Put some on your hands and try to scrub it off... very difficult, even with detergent.

[roverhi]

Originally Posted by markwesti

Originally my mast and spars were isolated pretty well with PVC plumbers tape (like where a fitting or plate) was mounted . Those areas are still good even after almost 40 yrs' . Also 1+ on Tef Gel and stuff like it . One thing I did though was to replace non structural things like lights with brass screws and Tef Gel . Brass hates Alum. a lot less than SS .

Aluminum HATES brass/bronze. Actually saw a mast years ago that had a rather large hole the size of the bronze winch base that had corroded through the aluminum. SS fasteners with TefGel, lanolin, blue LocTite etc work just fine and won't eat holes in the aluminum like brass/bronze.

[Flyingriki]

I built a new boom and found everything corroded solid. Used all new fasteners dipped in the goop used on aluminum electrical heavy cable ends at connections. Gasketed all SS items with plastic for sale sign material, so no metsls touched, and caulked the top edges to prevent UV degradation.
Talked to the new owner that made some mods later and he said everything was like new. Lotta work, but worth it.

[stormalong]

I have rebuilt my mast and boom a twice in the 27 years I have owned the boat. Both Duralac and Tefgel work very well.

I give a slight edge to Duralac for one reason. Tefgel tends to act at a lubricant. I found some rather critical bolts backing out of the mast shortly after the last rebuild. The boom gooseneck and the boom vang attachment. This was during very long beats to weather sailing from New Zealand to the U.S.A. I had never seen that with Duralac - it hardens up a bit. I washed out the Tefgel from those two attachments and replaced with Duralac - problem solved.

I used plastic sheet to make gaskets under any fittings on the spars. It is also a good idea to use one of these products on pop rivets. My mainsail track is held on by hundreds of pop rivets and when removing the old rivets for the last repaint there were signs of corrosion.

[Deltasailor]

Originally Posted by roverhi

Have used vinyl dodger window material and electrical tape as insulators. Could also try using caulk behind the fittings, butyl comes to mind but any caulk with fasteners only loosely fastened till it has a chance to set up and then snugged up should also provide insolation. Think lanolin or such would eventually wash out and not do the job flat against the mast.

Lanolin will not wash out. It's the stuff that keep sheep dry in wet weather.

[qwert]

Another plastic film you can use is mylar film. Its that stiff white very thin, (down to a few thou),film which used to be used by sailmakers for templates and is widely used as an electrical insulator in various devices. It is actually polyester which has excellent ,for plastic, uv life and is so thin it fits perfectly between stainless fittings and alu mast . I use duralac where you make a hole in the plastic for the fastenings.

[belizesailor]

Originally Posted by noelex 77

The most common techniques are applying products such as Duralac or Tefgel. The other alternative is to try and isolate the dissimilar metals as much as possible with plastic spacers.

These two methods can be used together.

Rubber is not ideal because of the carbon content. Often modern "rubber" products have little or no carbon but it difficult to be sure.

Anodes will not work on a mast.

Same approach Ive used. I cut plastic spacers from packing material (that evil thermoformed platic you need to cut away to get at parts...plenty of that stuff around). It holds up quite well. That plus Tefgel on screws etc. Rerigging now...been doing this all day! 😩