Warships have a system like this. For normal yachties it's probably a losing battle but I can see opportunities to make money here. Good management is probably the best you can hope for. There is no way you can isolate electrical currents once the vessel is in the ocean. We all need 12volts all the time [even when the main battery switches are off] to keep the radio presets, 12v bilge/float switch to pump out the boat while away [I don't]. Condensation or water in the bilge or water running down the sail track or even grime on top of batteries is enough to give stray voltages. It's the low voltage stray currents that are the problem. Timber vessels with normal moisture levels and metal fixings and you have a current while that boat is floating. The correct number of anodes and connected to what is being protected is what is important.

240 volts is much safer for a vessel floating. If your using shore power always use an earth leakage system on the wharf. On the boat, earth leakage switches on the systems you actually handle, TV, toaster, kettle etc is pretty much the minimum and fairly cheap to achieve. Pumps etc in the engine room don't matter so much.

Much of the low voltage problems we have can be reduced by simply a good paint system.

Started on the project today and installed an isolator for the main engine negative connection point. Did some testing then and found there was another small engine negative from the starter panel wiring loom. Still have to sort out the alternator charge light circuit. This I would image is only the tip of the iceberg.