ABSTRACT
This chapter only concerns the external hulls of ships, and other floating structures, together with external protuberances such as mooring cables and tethers. It deals with internal surfaces, such as ballast tanks, sea intakes and seawater piping. Irrespective of whether the ship is to be fitted with an Impressed Current Cathodic Protection (ICCP) system or sacrificial anodes, the first stage in the design exercise should be the same: determining the cathodic current demand. Propellers are commonly made from copper alloys, such as nickel aluminium bronze, which has good corrosion resistance to seawater. Other alloys, including cast stainless steel, are sometimes encountered, particularly on high-speed vessels. Howard Rogers described a consumable anode ICCP system in which the anode was an aluminium wire, up to 50 m long, that was trailed behind the ship. ICCP is also suitable providing it is appreciated that aluminium is amphoteric. It dissolves in both acids and alkalis.
