Chuck -

I am assuming you are plugged in to the dock. The neutral line creates a
common connection between all the boats in the marina. Although it is a AC
circuit the circuit itself really doesn't care if it is carrying AC or DC
current, as long as a circuit is completed.

On your shore power feed neutral connect a amp meter and measure both the AC
and the DC current. If it isn't your boat you will see current flowing from
your shore connection to your boat. You can either unplug all the boats in the
marina and systematically replug boats and see their individual effect on the
DC current flowing through you neutral leg of go to each boat and check them
individually. This is the easiet way of locating a DC fault on someone elses
boat. Strongly reccomend getting permission before un plugging anyone though!

A/C faults, although less of a zinc loss problem can be a bit more difficult to
find. The same method works though. I have found that most AC faults are
either due to miswired shore cables, internal boat wiring or most
common.........mis wired shoreside power system.

Let me know if this helps.

Dave