I posted last month about the continued problems I have had since my haul out and bottom paint/new bonding system done last summer. Here is the last post if anyone has the patience to follow or recap:
Some details about the "bottom problem"
I am in salt water in a notoriously hot marina. I used Interlux Racing Bronze bottom paint when I hauled in the summer. I had a little over nine pounds of zinc total once the bonding system was installed, to include a "regular size" diver's dream plate mounted to the transom on my 27 foot boat. I do not plug in to shore power while at "home" in the marina.
Upon hauling in October to see the damage, the marine contractor who applied the bottom paint checked the bonding system that my mechanic installed in June. It all checked out.....unplugged on the hard without the engine running. Calculations were done and it was discovered that my boat was "overzinc-ed" by about four pounds. Diver's dream was removed and a smaller plate was installed, one zinc was removed from the shaft as well. The comment was made that we "didn't know it was possible to over-zinc, especially at (my marina)". The consensus at the end of the day was that the combination of too much zinc and my bottom paint was causing a problem (one which I cannot intelligently explain again without assistance). The bottom was re-painted (with the same paint) and she was put back into the water.
Now, three weeks later, I have continued to worry that we have not solved the problem. It would be easy to blame the new bonding system, but in reality this could have been going on for a long while, as my previous bottom paint was pretty well gone (so it would have been difficult to detect this "boiling off" that we saw recently). While the bonding system checked out....there was no power at the time. Per Lee's recommendation I went down yesterday to check that the system is properly grounded, and it appears to be. Today I will go down and run the engine and the bonding with the engine running......as it seems logical that the charging/alternator system could be pushing juice to the through-hulls via the bonding system somehow?
Since that post I had one local marine electrician check everything out and he did not find any leaks or stray current, grounding problems, etc
Update as now: Diver popped into the water between maintenance dives to check things out. He found that the bronze paint was once again beginning to halo and bake off the forward raw water intake through hull and on the transom around the new zinc plate. I has him remove the zinc plate and had the mechanic, who was standing by during the dive, disconnect the bonding system.
Enter marine electrician #2 (big boy from Seattle). He determined that the application of the paint was incorrect. Because of the high copper content (not cuprous oxide) the paint should have been held off of any metal with either a gap or a barrier coat. Combo of high copper and bonding was causing the halo effect, which would worsen to total paint loss as happened in the summer. Diver just checked her again last week and the halo-ing seems to have been halted.
For the archives, maybe this will prevent this from happening to someone else down the line. When she needs bottom paint again I will likely NOT use bronze (though I really want to) and I will have the bonding system put back together. She is currently not bonded, and she never was in all of her 46 years before. But she was also in fresh water before me.