Calculations of the Protection Current Requirement

If the surface area cannot be obtained from structural drawings, the underwater surface area can be calculated from the following relation [1]  

The protection current requirement for aluminum ships is considerably less because of the dense adherent oxide films. The necessary protection current requirement is being clarified in current investigations [24] but good results have been obtained by assuming a figure of 10% of that for steel. With aluminum there is only a very narrow permissible potential range [25] (see Section 2.4) so that impressed current protection cannot be used because of the anodic voltage cone and only selected anode materials can be considered. 

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