When a large-sized ship, like a cargo ship or tanker, encountered a marine disaster and lost its ability to cruise, she must be towed immediately to a safe place to avoid a secondary calamity. In such a case, the course stability of tow and towed vessels would become a very important aspect from the viewpoint of safety for ship manoeuvring motion. An exact estimation of the hydrodynamic forces acting on tow and towed vessels is needed in order to predict accurately the course stability of tow and towed vessels by means of numerical simulation. However, any theoretical method estimating the hydrodynamic forces acting on towed vessels has not yet been established, particularly on the damaged vessels with a trim or heel angle. There are very few papers dealing with the hydrodynamic forces acting on capsized vessels with such a posture change as trim or heel angle. Therefore, an accurate estimation of the characteristics of hydrodynamic forces acting on capsized vessels with a large posture change is fundamentally necessary from the viewpoint of the safety in towing vessels. The hydrodynamic forces acting on a capsized model ship with a geometrical configuration and its characteristics have been investigated. The numerical simulation by using the measured hydrodynamic forces acting on the model ship has also been done in order to examine the manoeuvring motion and course stability of the towed capsized vessel.