Questions for Andina Marie
- From: RW Salnick <salnick@xxxxxxxxxxx>
- Date: Mon, 07 Apr 2008 11:55:55 -0700
We just completed our every-third-year haul out, and for the first time ever, we had something very unusual on the hull. Over a large area (approximately 1 meter across) around 2 bronze thru hulls on the starboard side and rising up towards the waterline, the bottom paint was gone. Not only the last coat, but all the accumulated layers going back to the beginning of time - right back to the epoxy-coated gel coat. The same thing was present around a different pair of thru hulls on the port side. And finally, to a lesser extent at the rudder gudgeon bearing at the heel of the rudder. Over the years we have owned the boat, we have never seen this before.
It was suggested to me that this was an electrolytic effect. It seems reasonable to me as well that it is. Would you agree?
The bronze thru hulls had no apparent dezincification. I had good opportunity to check one of them because I needed to replace it for unrelated reasons - it was quite sound.
We lost our prop nut zinc sometime over the winter (that is, it had eroded to the point where it departed when the prop started spinning), probably in February. So the boat was without anodic protection for the month of March. Is this enough time for this effect to appear? Or has it been underway for some time?
Finally, the bronze rudder gudgeon is connected electrically to the engine, as were the two thru hulls on the port side. The two thru hulls on the starboard side are not bonded. No other thru hulls on the boat were affected, not even the others which were bonded.
All electrical outlets on the boat are GFCI protected, and the boat is equipped with a galvanic isolator. I checked the water heater and found nearly 30 megohms between the element and chassis ground, which seems to be as good isolation as might be expected.
Can you help me understand what might have happened here?
Thanks in advance,
bob
s/v Eolian
Seattle
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