A CFD model for the prediction of the effect of biofouling on ship resistance was proposed. A modified wall-function was employed in the CFD software. This methodology enables the prediction of the effect of biofouling on ship resistance using fouling ratings. CFD simulations of resistance tests on flat plates of ship lengths and on the full-scale KRISO Container Ship (KCS) hull were performed. The effects of a typical as applied coating and different fouling conditions on the resistance of flat plates representing the KCS and of the full-scale KCS hull were predicted for varying service speeds.