This study proposes a general numerical tool for assessing the propulsion performance of ships in wind–wave conditions, focusing on delivered power demands and speed loss. This method uses an unsteady potential-flow panel formulation to determine wave-induced resistance and combined with a steady-state potential-flow/Reynolds-Averaged Navier–Stokes (RANS) methodology including body-force representation of the propeller for simulating self-propulsion characteristics to estimate the resistance in calm water. Comparisons between numerical results and experimental measurements for added resistance, calm-water resistance and delivered power served to evaluate the reliability of the procedure, showing a high degree of agreement. To show further applicability of the developed method, here it is applied to estimate a weather correction factor f_w which is needed for the Energy Efficiency Design Index (EEDI) [1] The f_w predictions resulting there from show very smooth agreement with values calculated from full scale operational records of similar vessel types, suggesting that not only is the method suitable for design stage assessments but also for exploratory performance evaluations in realistic environmental conditions.

Keywords: Sea keeping (SK), EEDI (Energy Efficiency Design Index), Weather factor, Delivered power (WFDP), Speed loss (SL), Full-scale measurements (FSM), Self-propulsion tests (SPT).