Indirect Measurements of Added-Wave Resistance on an In-Service Container Ship

This paper investigates a semi-empirical model used to estimate added-wave resistance on a ship sailing in waves. The model relies on measurements from a continuous monitoring system, and produces an estimate - the indirect measurement - of added-wave resistance, based on the difference between, on the one side, the measured power and, on the other side, a summation of theoretically calculated resistance contributions but neglecting the component because of seaway. Hence, the added-wave power is obtained as the surplus. The model has been applied to more than three months of full-scale data recorded on an in-service operating container ship. The results indicate reasonable levels of the added-wave power, emphasising that both positive and negative values are obtained, since the model is not restricted to relative wave directions forward of beam. It is found that following waves often lead to ‘negative resistance’, in fact creating a thrust, but, importantly, following waves can also increase the total resistance significantly.