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Old 06-03-2018, 03:54 PM
Senior MemberCaptains Club Member
Join Date: Feb 2003
Location: PA
Posts: 260

Originally Posted by Tony NJ View Post
I have the Garboard drains on my 34C Silverton. I boat in NJ in saltwater. and I replaced two of them about three years ago. They are Bronze with the T-Type plug. Yesterday while investigating in the bilge why I was taking on so much water, we noticed it was wet near the drain. We put our hand to wipe near the drain and one of the threaded bolts and nuts fell off. A bolt on each of them are bonded to my boats system. The bolts were stainless steel. Anyone have any idea if it was the bronze and the Stainless reacting with the saltwater? Boat is being hauled on Tuesday to have them both replaced, not sure if we should use SS bolts again or Bronze?
Tony, before I retired I worked a lot with heat exchanges and cooling water systems. We at times had problems with Stainless Steel corroding in areas that could trap water next to the stainless. The problem is that if the water is trapped it becomes acidic due to the reaction with the stainless steel when oxygen is not present.

The stainless protects itself by the very thin oxidized layer on the outside. If the oxidation layer is compromised and there is no oxygen to re oxidize it. The stagnate salt water then becomes even more acidic due to some chemical reaction that occurs. I think bronze is more resistant to crevice corrosion than stainless steel. Here is a link to an article about the problem. Good luck with it.

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