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Old 27-02-2011, 18:37   #1
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Interaction of Different Metals on Mast and Boom

I am begining to look in earnest at 1980's era Tartans. The boat I looked at (and an S2 that was also there) both had what appeared to be corrosion where fittings (not winches) were mounted to the mast and boom.

My common sense assessment was that the offending non-aluminum fitting would need to be removed, then an assessment make to determine the amount of structural integrity the mast or boom had lost. Then grind, fill, hopefully not weld, and paint. While none of the spots looked that bad, I recognize that in the extreme- it could require new spars.

Is my common sense view right?

Also if shouldn't the fitting have a bedding or insulating material to prevent this type of interaction?

Thanks

Bill
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Old 27-02-2011, 18:45   #2
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Re: Interaction of Different Metals on Mast and Boom

Negative, Sir!

Should not the fittings be in a metal that does NOT interact with the mast alloy? Like alloy, if the mast is alloy.

What are the winch bases made of though?

In any case it is nicer to end up with a corroded fitting than with a corroded mast, isn't it.

;-)

b.
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Old 27-02-2011, 18:55   #3
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Re: Interaction of Different Metals on Mast and Boom

Snore,

Need pictures to really tell you how to handle your problem.

The standard method for bedding dissimilar metals to a mast it to use a thin plastic sheet as a gasket and put Tef-Gel on all the ss bolts to stop galvanic corrosion.
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Old 27-02-2011, 18:57   #4
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Re: Interaction of Different Metals on Mast and Boom

Here, this thread is a good read. Fine or Coarse Threads

But one has to consider what he gets when buying older boats. After 30 years new spars might be a good decision.
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Old 28-02-2011, 07:20   #5
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Re: Interaction of Different Metals on Mast and Boom

Quote:
Originally Posted by Snore View Post
I am begining to look in earnest at 1980's era Tartans. The boat I looked at (and an S2 that was also there) both had what appeared to be corrosion where fittings (not winches) were mounted to the mast and boom.

My common sense assessment was that the offending non-aluminum fitting would need to be removed, then an assessment make to determine the amount of structural integrity the mast or boom had lost. Then grind, fill, hopefully not weld, and paint. While none of the spots looked that bad, I recognize that in the extreme- it could require new spars.

Is my common sense view right?

Also if shouldn't the fitting have a bedding or insulating material to prevent this type of interaction?

Thanks

Bill
Yes, your common sense view seems right to me. My wife was on a delivery when the boom snapped right where an SS bail was through-bolted. Then the SS shaft snapped just aft of the coupler. On the boom, it was clear from the residue that it had been rotting for ages. It was a freshwater boat sailed in salt for 11 years and this probably accelerated something that might have happened so slowly in fresh water as to outlast the owners.

Survey and close eyeballing will reveal much. Dye-testing will show problems in critical fittings like tangs and terminal ends, etc. So will a lightly gloved hand run down a stay's wires...any little snags are warnings.
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