It’s all about shore power and underwater metal corrosion, for example your sail drive on our Seawind. I struggled with the concept. Why buy a galvanic isolator? A post from Charles Fort was helpful.
When SV Kiskadee is plugged into shore power, it is electrically connected to everyone in the marina via the green wire, the grounding conductor. All boats are part of one galvanic cell.
The weakest metals, like your aluminium sail drive and anodes will corrode because there is always current in a galvanic cell. The weakest metals with the most surface will function as a ground connection to earth, for the whole dock.
It’s one electric circuit. So your anodes are also contributing to the corrosion protection for all the other yachts plugged in. Your fresh, unpainted anodes will be sacrificed for all your neighbors.
To solve this problem there is the galvanic isolator. Its successor is an isolation transformer, more expensive, more weight, electronically monitored, but functional the same. When connected to shore power on a regular basis, you need a galvanic isolator installed in your shore power system.
Look for a marine rating when buying a galvanic isolator. The isolators must be rated for system amperage. If you have a yacht with an older isolator installed, or if you experience at any time a high power surge from shore or lighting or … test your galvanic isolator. Here is a simple instruction with a multi meter.
Worn anodes are still the primary cause of corrosion on engine, hull, sail drive, propeller and rudder. If anodes seem to be suddenly wasting away, you may be a victim of galvanic corrosion. Shore power and no protected of a galvanic isolator is probably the second common cause of corrosion. Local rusty spots special on stainless steel components are either surface contamination or a leaky, shafted 12v AC wire to a sidelight etc. Also easy tested with a multi meter. Metal corrosion is sometimes hidden or out of sight. Can be prevented with painted coatings, PVC busses, isolating kit or using the same metal.