To prevent corrosion of the hull, propeller, rudder and line shafting.

The anode does not waste away as it is insulated from the hull.

The principal of the impressed current system of cathodic protection is to set up a flow of electricity, opposing that naturally generated by two metals, i.e. the cathode and the anode. Care has to be taken though, as it is as harmful to supply too much current as it is too little. Changes in temperature, surface conditions of the metals and conductivity of the electrolyte demand that the current and therefore the PD should be changed, this automatically controlled and monitored by a thyristor control circuit.