Objective  To investigate ship power characteristics and the difference between the towing model and self-propulsion model for ship motion response in waves, numerical simulations of ship self-propulsion performance in waves are carried out.

  Methods  In this paper, the KCS ship model and KP505 propeller model are selected, and the unsteady Reynolds-averaged Navier-Stokes (URANS) method is used to carry out computational fluid dynamics (CFD) simulations of ship self-propulsion in waves. The in-house URANS solver HUST-Ship and in-house structured dynamic overset grid code HUST-Overset are combined to solve the motions of the self-propelled ship in waves, and the improved body-force model is selected as the propulsion model. Towing simulations for KCS with two-degrees-of-freedom (DOF) in waves and self-propulsion simulations with 3-DOFs under different wave conditions are carried out, and the differences between these methods are discussed in detail. Finally, the components and their specific proportions of added power during ship self-propulsion in waves are analyzed in detail using the logarithmic analysis method.

  Results  Regarding the added power of a self-propelled KCS in waves, the added resistance is responsible for 74%-77% while propulsive efficiency accounts for 23%-26%, that is, the added resistance occupy a larger proportion.

  Conclusion  Reducing ship motion to decrease added resistance is the most effective approach to reducing added power.