Help needed with Reverse Polarity & breaker Issue

[Domroberge]

Hi everyone!

For the second summer in a row, the breaker located at GFI electrical box in the forward sail locker keeps on tripping periodically when connected to shore power. When I hauled out the sailboat last fall of 2023, I discovered a serious discolouration/oxidation around the Frigoboat plate under the boat. See Pictures! During this time, the reverse polarity light on the main panel comes on very faintly when the sailboat is connected to shore power. We suspected that our sailboat is either affected by stray current at the marina, or that we have some type of electrical leak from our boat.

This past spring prior to launch, I had the Frigoboat plate changed. The technician recommended that we also install a Dynaplate. This was done in addition to changing my magnesium anodes (we sail in fresh water) on the sail drive again this year.

Despite these changes, our sailboat GFI breaker on-board the sailboat kept on tripping this summer, and I have noticed similar discolouration of the hull when diving under the boat while at anchor this summer. I have been working with an ABYC certified electrician, but the root cause hasn't been found yet.

The issue started after I had our 4 AGM house batteries changed to 3 Victron lithium batteries with a new Victron changer/inverter for the house batteries.

The engine battery and 4 AG batteries for my windlass and bow thruster are still charged by a separate charger.

Our sailboat is a 2011 Jeanneau 50DS

Has anyone seen this type of problem? Can anyone suggest a way to diagnose the problem?