Really dumb electrolysis question. Really, it's like a sign saying "low season"...

CreakyDecks said:
I'm not sure electrolysis would be a problem. When I recently rebuilt my old push bike, the aluminium wheel rims were perfect but the (presumably once chromed) mild steel spokes had rusted to almost nothing.
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It's not electrolysis anyway, it's galvanic corrosion; electrolysis is when a chemical change is forced by applied volts. The OP got the wrong term.

Bike wheels usually don't go to sea as often as boats. Galvanic corrosion of aluminum is a real problem in a marine environment. There have been many reports on this forum of hardly any mast metal left behind a stainless fitting, and how many times do people complain that their outboard engine bolts are seized in place? With copper, it would be far worse. It's not worth the risk.
 
Angus, evidently you know your stuff, but you're alarming me now...if I go through SWMBO's jar of pennies and find a couple of the 'eighties coins which won't rust, will they themselves degrade relative to the stainless steel bar they'll sit on, or will they cause galvanic corrosion of the bar?

Not sure where the aluminium question came from... :rolleyes:
 
dancrane said:
Angus, evidently you know your stuff, but you're alarming me now...if I go through SWMBO's jar of pennies and find a couple of the 'eighties coins which won't rust, will they themselves degrade relative to the stainless steel bar they'll sit on, or will they cause galvanic corrosion of the bar?

Not sure where the aluminium question came from... :rolleyes:
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If you look at a galvanic series you will see that there is about 0.2 volts between 316 stainless steel and bronze, bronze being the more anodic of the two. Not a great difference but perhaps significant if they were continuously immersed in seawater.

However your top swivel is not continuously immersed in seawater so there will be no problems.
 
Thanks Vic.

Out of interest, if it's necessary for whatever reason to have two contrasting metals close together, is it possible to protect the inferior of the two, by adding yet another, even more base than the inferior? (Umm...is that the whole point of sacrificial anodes? :o)
 
dancrane said:
Angus, evidently you know your stuff, but you're alarming me now...if I go through SWMBO's jar of pennies and find a couple of the 'eighties coins which won't rust, will they themselves degrade relative to the stainless steel bar they'll sit on, or will they cause galvanic corrosion of the bar?

Not sure where the aluminium question came from... :rolleyes:
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Stainless will protect the coins. I didn't know whether they were touching aluminum or not, but if they were, it would cause serious problems. My swivel is aluminum.
 
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dancrane said:
Thanks Vic.

Out of interest, if it's necessary for whatever reason to have two contrasting metals close together, is it possible to protect the inferior of the two, by adding yet another, even more base than the inferior? (Umm...is that the whole point of sacrificial anodes? :o)
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It's not being close together than matters, it's having a low resistance electrical circuit between them and both being in a common electrolyte (usually salt water on a boat) that matters. You protect the more reactive metal with sticky gunk - barium chromate based usually. Duralac is the most common. An alternative is to isolate electrically the two parts.
 
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VicS said:
However your top swivel is not continuously immersed in seawater so there will be no problems.
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For metals further apart continuous immersion is not necessary, salty damp is enough. The corrosion you get on carbon sails between the graphite and the stainless fittings is a significant problem.
 
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FWIW copper ferrules are used on Talurit splices in stainless steel wire.

No signs of any galvanic action around mine
 
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