Model experiments have been carried out to investigate the hydrodynamic forces acting on ship in even keel and trimmed conditions. The relations between this force and load condition of ship were proved, and the linear and non-linear derivatives in manoeuvring mathematical models for fitting the measured results to describe the forces were also examined semi-empirically by using the model tests of various kinds of ships and applying a theoretical approach. Finally, the approximate formulae for practical application in estimation the lateral force and moment on ship in manoeuvring motion.