On the resistance and speed loss of full type ships in a seaway

This paper presents results of a systematic study on the resistance and speed loss of full type ships in waves. The percentage resistance-increase in waves against experimentally measured calm water resistance data was estimated by use of two alternative empirical formulas, namely one proposed by the authors and the other one as recommended by ITTC. The obtained results clearly show that the percentage resistance-increase and the associated (involuntary) speed loss are strongly dependent on ship's absolute size, loading condition and the operating seaway conditions and they can be satisfactorily quantified. This should be taken into account in the ship design process, when determining the sea margin for the selection of the machinery and propulsion system, when analysing sea trials and/or when preparing scaled model experiments to assess ship's performance in realistic seaway scenarios.