What is cathodic protection?

Water conducts electrical current, which enables different metals in close proximity to create a circuit.

On a typical leisure vessel the area under the stern features a prop shaft, a propeller, a rudder post and perhaps metal through-hull components all within a small area and linked electrically through the medium of sea water. It’s the equivalent to a low-power battery, which would be unremarkable apart from the fact that the electric charge gradually and almost imperceptibly corrodes the various terminals – ie your boat’s expensive metal fittings.

The solution lies in applied chemistry: install a sacrificial chunk of the correct metal (an anode) wired to the vulnerable metallic items and the circuit will corrode the anode, leaving the more valuable bronze and stainless steel items unaffected.