I have seen this erroneous alarm issues if the battery bank is either in poor condition (old batteries). Or the battery charger is leaking AC...
Yes, I have run a few vessels with Humphrees INTERCEPTORS. They work well on vessels when you're doing over 25 knots, as good as fin stabilizers...
You need to plumb the galley sink directly overboard, there is NO reason it should drain into the holding tank.
AND take pictures and print them all out and in a book, so you can simply look for something via pictures before opening ALL of the voids again....
There are so many variables, electric or hydraulic, size etc.. Honestly, I cut my teeth running a 58' Hatteras YF, the stern of those boats walk...
