Aluminium boat - stray current

[mcarthur]

Originally Posted by Taswildlife

I also fitted a SeaBis (stray current detector) to my steel yacht as mine was blowing hand sized patches of good paint off at the waterline and showing clean etched metal when the paint came off. I eventually solved all my stray current issues and now my electrics are completely "above ground". I had issues in both engine battery and house battery circuits. In the engine circuit it was the usual suspects of a perminant negative bolted to the engine block without an isolator and non isolated alternators. I also had a normally closed fuel solanoid that required negative current to the engine block to be open. That had to go and I built a pull knob and cable that starves the engine of fuel.
In the house battery circuit I had to replace the VHF antenna with a ground plain independant version and there was some other stuff I cant remember as all repairs were done bit by bit over time as changes were made.

My advice would be to isolate house and engine circuits and disconnect both leads from the engine battery and see if there are faults in the house system. To sort this out with the SeaBis system of diagnosis you have to begin disconnecting wires from the negative bus bar leaving each one off. It must be noted that if you have three faults your sray current detector won't show "all clear" until the third wire is off. You may then have multiple wires off. You may even have them all off and still be showing a fault so you will need to begin disconnecting things like bilge pumps or wires from your positive bus bar. Once you have reached "all clear" begin touching wires to the bus bar one at a time. If they are not causing the fault put them back on. If they cause faults tag them and leave them off. You then have to work out where the wires go or what's not working to find out what was causing the fault. It could even be a chafed or submerged wire
I notice the fault alert that started this thread was a positive warning showing so I wouldn't be sure that this is an earth issue. Your electrician is right this can take some time but it's worth the effort

Thanks Tas for the procedure which I assume would work the same for the VDO as for Seabis. Yes, it's usually a -1 LED on the negative scale of the VDO gauge. Sometimes -2 LEDs for a moment or two.