It is well known that the change of the character of the underwater hull surface influences the overall performance of a vessel in service over the period between dry-dockings. These changes in surface character and structure are mainly due to mechanical damages of the coating film and to biofouling accumulating on the surface, see figure 1 for illustration. The average impact of the surface degradation on the propulsion efficiency of a vessel over a five year docking interval has been reported to be on the order of 15% to 20% as indicated in [1, 2]. For different types of fouling the additional shaft power demanded to maintain a certain vessel speed has been estimated to amount to between 9% for light slime and up to 84% for heavy calcareous fouling [3], see table 1. Given that the fouling protection abilities of different antifouling coatings on the market vary and that the impact of this variation is so significant to those paying the fuel bill, one needs practical ways to evaluate the in-service performance of antifouling coatings for individual vessels.

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