Lifted a large motor cruiser out the other day, she had been on her moorings for a couple of years with only a few trips into salt water. The zinc anodes just forward of the prop shafts had vanished leaving a couple of studs as silent testimony to their passing to oblivion. Yet the anodes on the trim tabs had virtually no wasting at all. Zinc anodes in fresh water after a couple of months suffer with a type of calcification and to all intent cease to be effective.
The vessel had been on permanent 240v shore power and the owner had carried out a great deal of retro fitting of electrical equipment and it all looked very swish. Lurking behind all those dials, switches and cats cradle of wires I would rashly bet next months pocket money that we have a tiny bit of stray current leaking out. From the state of the anode studs which looked like they had been sandblasted to death I would imagine the fishes had been driven crazy with all the anode fizzing that had been going on under that boat.
Even had the owner fitted the correct anodes for fresh water, they would still have dissolved away at an alarming rate. The propellers had signs showing erosion of the zinc in the metal was taking place and if unchecked will have ruin the propellers. If you bought your boat to get away from the worry and stress of modern life stop reading this now and turn the page.
The 240v power supply is often the main culprit with this highly active anode wasting, and highlights the need to fit a galvanic isolator. Today’s C E standards like EN ISO 13297 ensures the shoreside earth system is connected to your vessels bonding system and just about everything else on the boat including your anodes to ensure your R.C.B. works. The downside is that electrically speaking your boat is connected to everything else in the marina on shore power. Electrically all the boats are now one, you have an anode which works and somebody else’s has failed, your anode will now protect him and waste away, your sterngear is at serious risk. It can get worse, has the Boatyard got the earth connected correctly ashore?