Corrosion of fittings

[Jon Bastien]

Hello all, I'm posting this one as a favor for a friend at the local sailing club... He recently purchased a Cape Dory 25, and has noted that he's having severe corrosion problems with the bronze hardware on board. On his boat, there's bronze a-plenty, so this has him VERY concerned. In a matter of about 6 months, the trim on the ports, the winch hardware, and the thru-hulls(!), cleats, and all of the other miscellaneous fittings have gone from bright, shiny, new-looking equipment to being completely covered in green corrosion. He'd like to know what he can do to prevent this kind of corrosion in the future- Is there anything he can do? He's already chased through all the wiring on his boat looking for stray currents and bad grounds, but found nothing unusual. Will bonding everything together help? Is there any way to attach a zinc to prevent this corrosion (and just how WOULD you attach a zinc to a winch, anyway)? ...Or is this just a matter of needing more frequent application of a little elbow grease and metal polish? It should be noted that our sailing club is in fairly well-protected and shallow waters, with the city marina in the same inlet- the water is VERY hot, electrically speaking. The CD25 has an inboard diesel, and the very large zinc that was placed on the prop shaft last May was almost half gone when he hauled it out last week. Here's hoping some of you 'electrically talented' folks can help us out. Thanks in advance,--Jon BastienH25 'Adagio'(with sympathies for a beautifully maintained but electrically battered CD 25 next door)

 

[david lewis]

Bronze fittings on Cape Dory

metals are not as you see them on boats in the natural world. they are in the form of metallic ores, rust, etc. man takes these ores, adds a lot of energy and makes metal products, he also adds some alloying elements like carbon, molybdenum, chromium etc for certain desired properties. These metals want to immediately start returning to a lower energy state. This happens by oxydation. What you describe is not galvanic corrosion but rather oxydation of the metal. Most metals form a thin oxide film that then protects it from further oxydation, or at least slows down the reaction. So to solve your problem the trick is how do you keep oxygen away from the metal. The previous owner probably polished everything to sell the boat, but the natural state for these metals with a slight oxide layer is the color you see. Your choice is to plate the metals with chrome or nickel or try to find some coating that will keep the oxygen out, or polish them all the time. This is why newer boats don't use these materials anymore, prefering chrome plated bronze, or stainless steel.hope this helps even if its not what you want to hear.dave

 

[David]

Cape Dory Fittings

If the condition you are describing is on the above waterline bronze then it is probably "false verdigris" which has a greenish tint to it. This is not corrosion but an oxygen based discolorization. After cleaning, a clear laquer coating will protect. If you suspect otherwise it is best to have a corrosion survey.

 

[TOM MCNAMARA]

CORROSION

If I could understant their words I would agree with them. But I do think the previous owner shined the hell out of them.========== Chrome them for about 300 dollars or more.

 

[Been There]

Leave them be

Any bronze kept outside naturally develops a green patina. Very quickly. I bet your friend can't finish polishing it all before the first pieces are turning green again. This doesn't hurt the metal. Don't believe me? Go to a museum. There are lots of bronze artifacts from the bronze age. And they weren't polished through the millenia, though some museums try to make them pretty. Tell your friend to stop worrying, and go sailing.