Cathodic Protection
Cathodic Protection (CP) is the primary method of protecting the submerged steel of a hull, ballast tanks, sea chests and rudder from electrochemical corrosion. It works by making the steel the cathode of a cell, so that corrosion is driven onto something else instead.
Two systems are used. Sacrificial anodes — blocks of zinc or aluminium bolted to the hull and in tanks — corrode preferentially and are renewed at each dry-docking. An Impressed Current Cathodic Protection (ICCP) system instead drives a small protective current from hull-mounted anodes powered by an onboard controller, adjusting automatically as conditions change.
Corrosion is the slow, relentless enemy of a steel hull. Cathodic protection, together with the paint coating, is what keeps the structure sound between dry-dockings; anode wastage is a standard survey item, and a failed or under-sized system shows up as accelerated steel loss that can become an expensive class and repair problem.
What is the difference between sacrificial anodes and ICCP?
Sacrificial anodes are blocks of a more reactive metal that corrode away in place of the hull and are replaced each docking. ICCP supplies a controlled protective current electronically, lasts longer and adjusts automatically, but is more complex.