Discolored wheels

[aah924]

While I have my boat, '72, 36' Hatt. on the hill this weekend to do some trim tab work, 1 of the foreman at the yard walked by and asked what type of electrical problem that I had. I said that I wasn't aware of one, and he said that my wheels were discolored, so I had a problem somewhere. My zincs were also corroded and had been replaced in the early spring. He briefly told me to use a test meter and check circuit breakers. Does anyone else have any info on this or have had this problem occur? Any ideas on where to look first?

[jim rosenthal]

he thinks you have a DC current leakage which is getting into the bonding system and affecting the underwater metal parts. Generally it is NOT the breakers; look first for bare wires in the bilge areas, which will leak current into bilge water and are probably the most common source of this kind of thing. I would start with a thorough inspection of all the wiring and all the wiring ends.
Marine battery chargers are occasional culprits on this since they are constant sources of DC. One way to look at this, although not the cheapest, is to install a meter such as the Link 20 which will tell you when any DC is going out of the battery and coming back, and how much. You can also get a professional corrosion consultant to look at the boat's electrical system; in some cases this is worth it. But, according to my friend at Yacht Electronics Systems here in Annapolis, the most common cause of stray DC current is old wires in the bilge.

[captddis]

I think he meant that you turn everything off then turn one breaker on at a time to see if you get a reading on the metal. I agree with Jim about the DC and float switch wires etc. Also suggest a Galvanic isolator if you do not have a isolation transformer.

[jim rosenthal]

I should have mentioned that. Basically isolators are diodes that go in the AC ground leg coming in. They will block most low voltage DC and prevent a lot of electrolysis problems.
Two very good books: Metal Corrosion In Boats, by Nigel Warren, and Boatowner's Guide To Corrosion, by Everett Collier. Both from International Marine publishing, both very readable (anyone who can have me staying up late to read about 400 series stainless and CuNi alloys writes well, or maybe I'm even more of a geek than I thought), and if you read them you will know a LOT.