Since the interim standards for ship manoeuvring performance A.751 (18) was adopted in International Maritime Organization (IMO), it became very important to predict the ship manoeuvring performance with high accuracy at initial design stage. In this paper, the theoretical prediction method for the hydrodynamic forces acting on ship hull which can be took into the effect of frame line configuration is proposed based on the slender body theory. Furthermore, it is found that we will be able to predict the course stability of ships with comparatively accuracy from the results of numerical calculation for the hydrodynamic forces acting on ship hull. Therefore, it is considered that the present method will be useful to evaluate the course stability of ships at initial design stage from the viewpoint of practical use.