Improvement of prediction methods of power increase in regular head waves using calm-water and resistance tests in waves

This paper applies load variation method to predict speed-power-rpm relationship along with propulsive performances in regular head waves, and to derive overload factors (ITTC, 2018). ‘Calm-water tests’ and ‘resistance test in waves’ are used. The modified overload factors are proposed taking non-linearity into consideration, and applied to the direct powering, and resistance and thrust identity method. These indirect methods are evaluated through comparing the speed-power-rpm relationships with those obtained from the resistance and self-propulsion tests in calm water and in waves. The objective ship is KVLCC2. The load variation method predicts well the speed-power-rpm relationship and propulsion performances in waves. The direct powering method with modified overload factors also predicts well. The resistance and thrust identity method with modified overload factor predicts with a little difference. The direct powering method with overload factors predicts with a relatively larger difference. •The load variation method is applied to predict speed-power-rpm relationship along with propulsive performances in regular head waves, and to derive overload factors (ITTC, 2018).•‘Calm-water tests’ and ‘resistance test in waves’ are used.•The modified overload factors are proposed taking non-linearity into consideration.•The load variation method predicts well the speed-power-rpm relationship and propulsion performances in waves.•The direct powering method with modified overload factors also predicts well.•The resistance and thrust identity method with modified overload factor predicts with a little difference.•The direct powering method with overload factors predicts with a relatively larger difference.