THE PREDICTION of wave-added resistance is important for several reasons. In heavy weather safety aspects are most important.Is the ship able to sustain sufficient speed to maintain heading and is the main engine able to cope with the overload? In moderate weather conditions, fuel economy is most important. In these conditions, the power demand increases when speed is sustained or when sailing at constant power the added resistance will result in speed loss.The safety and economic aspects can already be studied in the design stage with so-called operability studies. These studies account for the actual service conditions and assist the designerto optimize for service conditions and to select an appropriate service margin. When the service margin is too low, safety might be at risk and the reliability in terms of arrival times will be low.When the service margin is too high, the main engine will run most of the time at inefficient power settings and (future) energy efficiency design index (EEDI) requirements might not be met.Within the present work we compared two recently developed empirical prediction methods, two established empirical methods developed in the 1970s and experimental data in regular wavesand irregular seas.