Victron Energy Galvanic Isolator VDI-32

The galvanic buffer prevents electrolytic corrosion. It blocks direct low voltage current entering your boat from the ground wire of the beach power supply. These currents can cause corrosion on parts in contact with the water such as the hull, propeller and shaft under the boat.
The galvanic isolator consists internally of two diodes which are connected in parallel. When connected in this way, the diodes allow current to flow in both directions, but only above a certain threshold voltage. The voltage at which the diode combination becomes conductive is 1.4 V DC. The isolator is connected directly after the 230 V connection of your boat. The voltage across the galvanic isolator is greater than the potential difference between metals. The result is that this low voltage is not allowed to pass through, and therefore the galvanic isolator will prevent electrolytic currents. However, if there is a (higher) fault voltage in the AC circuit, the diodes will allow current to pass through and the leakage current protection device will break the circuit.