Electrical Problem on 1983 Morgan 462

My friends Russ and Shelley on the sailing yacht Jacana asked me to post this problem for them since they have spotty internet.

We just discovered that we have a current leak on the boat. We found out by noticing that our sacrificial zinc (2-lb plate bolted on the hull) had dissolved in 3-months. The previous plate lasted 3-years. Our drive-shaft zincs are also being eaten at an increased rate.

I disconnected the ground wire from the zinc and measured approximately 15 milli-amps using a cheap digital meter. I then turned off all the power on the boat and switched off the 110v circuit breakers on the dock. We plug into a 50-amp plug and split it into two 30-amp lines which plug into the boat. The reading remained the same. When we unplug the cables from the dock the reading goes to about 4ma.

The marina sent an electrician down and with their (more expensive) meter could see no current. Measuring from neutral to ground on the dock, my meter showed the 15ma.

Using a formula I found on a forum, 15ma seems low for the rate of consumption of zinc. I put the discrepancy down to the quality of my meter.

To determine if it was the power grid or another boat, we began unplugging other boats, one at a time. With most boats, there was no change. Two boats, one a glass boat and the other a steel boat, caused a large increase (to about 75ma) when either was unplugged, and about 85ma when both are unplugged. This confused me. These boats zincs will be checked shortly.

The marina's first response, naturally, was that they saw no problem on the grid, and it must be my boat. I think I finally convinced them that there was a problem and that it was not on my boat. There are come communication complications, as we are in Panama, the electricians have limited English and I have limited Spanish.

The boat is a 1983 Morgan 462, with a Perkins 4-236 engine, a Northern Lights 8KW generator, 2 built-in air conditioners, fridge, freezer and the usual complement of electronics and electrics. I am fairly confident that my grounding system is good. A fitting on one of my through-hulls is showing a fair bit of green corrosion (it is wired to the zinc), but I have seen no other evidence of metal loss.

I do not see this current while the generator is running, nor while the inverter is on.

I have reviewed my maintenance logs and can see nothing in them which might be relevant.

Here are my questions.

1. Can I safely say that the problem is not on my boat, and if is, what can I do to troubleshoot and cure it? I am considering two isolation transformers, one on each 30-amp circuit, but that is a lot of money and freight.

2. If it is not my boat at fault, how do I prove that it is the marina's (or another boat's) problem.


Any suggestions or ideas would be greatly appreciated. My short term solution is to back out and go on the hook.

Thanks rcrapps for the great ideas!!

Does anyone else have any suggestions??