Galvanic corrosion & ways to prevent it

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Galvanic corrosion & ways to prevent it

Postby rick_bradshaw » Sun May 09, 2010 1:36 am

Situation:
White powder on 2 bronze seacocks located in the lazarette (the seacock furtherest aft on each side) at the area where the flange base is molded to the seacock barrel. Checked the power from the dock and discovered 1.5 v on the neutral to ground connection. Found another empty slip on the dock and checked it. Found no current. Checked a few more and found another that had the same voltage reading as ours. (Note: this powder has appeared within the last week or so.) We apparently are on the same "leg" as that slip.

We changed AC connections to a slip close that did not have a problem. Checked our cord and did not show any issue. However, we, after 2 days plugged in to the new "leg" are seeing a "tiny" bit of white powder in the are where it was before. Seems there is an indication that there still some problem but not as severe.

We are a bonded boat. The boat beside us is not plugged in (gone back to Australia for hurricane season & we plugged in to their power) There is an old, metal (steel) boat that arrived about 2 months ago across the dock and up 1 slip. From what I have read they must have a galvanic isolator on a steel boat and that they may also give off stray current. I've also been reading that our bonding circuit may be "collecting" these stray currents through our forward seacocks and transmitting them out our aft seacocks. The accuracy of that, I haven't a clue. Only what I read.

For now, I think the issue is small. However, that week or so caused enough metal to disappear that I can feel the difference to the touch. If I can't get it stopped completely, I will need to replace 1 or 2 seacocks. I'm preparing to be ready for that if need be.

Questions:
1. Shore power may have caused this but is there anything else that might have (there was no indication prior)?

2. What can I do to ensure that this situation doesn't happen ever again (if that is possible)?

3. As I understand it, galvanic isolators only cover about 1.2 v so this would not have covered it all or would that have even helped at all?

4. Anything else I need to know or should know that I don't? (BTW: for me, electricity = smoke and mirrors and I feel like the mirror is cracked and all the smoke has escaped. IOW, I'm no where near being an electrician; yet.)

Thanks in advance. Any and all help and information will be greatly appreciated.

We also leave in the morning for a 27 hour bus trip back to the u.s. so I may or may not be getting email for a few days. Will be back in Mexico in a week. Wish this had come up earlier since if we need parts I could bring them back. Am leaving plugs next to the seacocks and asking someone to check just in case.
Rick

s/v La Vita
1987 HC 33T #136
http://la-vita.us/blog/
rick_bradshaw
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