Isolating stainless from aluminum

[HukilauMike]

I will be installing a new soft boom vang this spring on my Oday 23. My current plan is to mount stainless bails on the boom and mast. How can I isolate the stainless bolts and fittings from the (painted) aluminum boom and mast? Any other suggestions/alternatives to the above plan? Thanks.

 

[Warren M.]

Isolating Stainless

You can isolate the stainless bail from the aluminum boom by inserting a clear plastic spacer between the washers and the boom.These are available at West Marine or any decent marine store. Or do what I do: make your own small isolators out of discarded rubber bike, or similar, tubes. I use the stainless washer as a template. Works for me.

 

[Steve]

What happens with SS and Aluminum?

What happens when stainless and aluminum touch each other? I bought a 1992 H28 this fall and there are 7 stainless bolts holding the aluminum quadrant onto a stainless rudder shaft. There are also 2 stainless bolts holding an iron rudder stop bracket onto the aluminum quadrant. Can I expect trouble in this area? I also have numerous stainless fasteners holding things onto my aluminum mast and boom - am I in trouble there also?

 

[Tim C350 April IV]

Dissimilar metals

Steve asks what happens when stainless and aluminum touch each other? In general, the two are referred to as "dissimilar metals" and you can have corrosion begin in the less nobel (generally "softer") of the two metals - in this case, the aluminum.Another thing that happens is that the hard stainless fastner can sieze in the softer aluminum spar. It's good practice to use anti-sieze compound (see the link) on the threads of a stainless fastner before installing it into aluminum.Tim (not a metalurgist) BroganApril IV C350 #68Seattle

 

[Rich (also not a metallurgist!)]

Theory and practice

In theory you would want to isolate the metals, but in practice the aluminum spars are coated in such a way as to make this unnecessary. I don't know of anyone with an aluminum spar that doesn't have stainless screws holding things into it and when my rigger installed my new stainless steel boom vang last year they simply attached the works right to the aluminum spars. the paint on your spar should protect it, but putting a little vaseline on the screw before inserting it should be an adequate barrier.

 

[Stu Jackson]

Use Lanacote, too

nm

 

[Gord May]

Not vaseline

Tim & Rich are both on the money.I wouldn't use vaseline tho', as it liquifies & evaporates in hot weather. Use an anti-sieze compound. Don't scratch the paint (Alum).

 

[Steve Dion]

Tef-gel from W/M

The spacers will do a fine job of keeping the screw/bolt from coming into contact with the aluminum, but what about the threads. The threads are where the problems really lie.You should apply a product like Tef-gel to the threads to prevent them from gauling. When thin happens it can sometimes be impossible to remove the screw without drilling and retapping the hole.We just had this happen on one of the boats in the harbor. Probably going to work on it this weekend.

 

[Fred Ficarra]

Great stuff, but

when I went back to my local WM store last year for a refill, they no longer carried it. They had a house brand instead. It didn't stick as well and cost almost as much as the real thing. Typical West Marine. They do a lot of that since they went public. Money is all that counts. I had to order the good stuff on line. Here ya go,,,http://www.wolfwire.com/tefgel/Tef-Gel.htm

 

[Dan18277]

Curious

I redid an old aluminum mast. It had SS fasteners. There was no corrosion. Does the corrosion require salt air/water? Both aluminum and SS are relatively resistant to corrosion, although under the right conditions, salt is very hard on aluminum.

 

[Alan]

I just pulled the ...

..anchor roller/stem fitting off my boat to add the support for a retractable bow sprit. I was surpised(though I shouldn't have been) to find the amount of galvanic corosion under the SS stem head on the aluminum toe rails. When I reassemble there will be a rubber insulator between the two.

 

[Bob Camarena]

Wide Electrical Tape

I've used wide, black plastic electrical tape. It will adhere to the mast and can easily be trimmed after the fitting is mounted. As others do, I use and anti-seize compound on the screws and bolts. By the way, it's better to drill and tap for machine screws than to use sheet metal screws. Not only is it stronger, but as the sheet metal screws cut their way in, they're going to cut through the anti-seize compound and compromize your isolation.