Cathodic protection of ships

Ship cathodic protection can be divided into sacrificial anode protection and impressed current protection:

Sacrificial anode protection connects a more active metal or alloy to the protected metal to form an galvanic cell. In this case, the more active metal (such as aluminum and their alloys) is corroded as the anode of the corroding battery, and the protected metal acts as the cathode for protection purposes.

1. Design and Calculation of sacrificial anodes The manufacturer or supplier of sacrificial anodes shall provide accurate design calculations and layout drawings with the supply. The maintenance personnel shall review the calculation and layout drawings. Design calculation of sacrificial anode The design calculation is to carry out design calculation for the parts that need cathodic protection (the parts below the waterline of the hull, the interior of the cargo tank and the ballast tank). Its contents shall include: the area of the protected (area), the protection potential range, the protection current density and the total protection current and the type, size, form, weight, capacitance, current and service life of the sacrificial anode.

2. Sacrificial anode layout Drawing Sacrificial anode layout drawing shall conform to the requirements of actual calculation book. (When updating, reference should be made to the design data of the original ship) the material and model of the sacrificed anode, size of the sacrificed anode, installation form and installation requirements of the sacrificed anode, and coordinate position of the sacrificed anode layout shall be included. The sacrificial anodes for hull plates can be arranged in the whole ship or only in the stern according to the requirements of the construction manual. The sacrificial anodes for hull plates are usually arranged evenly and symmetrically along the streamline before and after the bilge keel and the bilge keel. Sacrifice anodes for propeller and rudder shall be evenly arranged on stern hull plate and rudder. Because the sacrificial anodes will cause cavitation corrosion to the propeller, the sacrificial anodes should not be placed on the hull plate within a little 300mm from the propeller blade and in the anaerobic condition of single-propeller ships (see Figure 1).