This paper discusses a procedure to optimize ship hull forms for minimum required power and best wake field quality, based on CFD computations of the viscous flow. A flexible and effective definition of parametric hull form variations is used, based on interpolation between basis hull forms. All RANS computations were performed for full-scale Reynolds number. An initial optimization has been obtained neglecting the ship's wave making. Clear Pareto fronts and trends in the solutions are obtained in a systematic variation study for the afterbody of a chemical tanker. In addition we performed a systematic variation using RANS free surface, to study the influence of wave making on the computed trends. As a result, a further decrease in the object functions could be obtained and another hull form appeared to be optimal.