A sailing boat is mainly divided into two different parts, the topside and the bottom. Thefirst one is in contact with the air and the second with the water.When the boat is in equilib-rium, the forces on the topside,created by air, which are mainly forces on the sails, are equalto the forces on the bottom which are generated by the water. Those forces are created bythe interaction between the fluid and the solid body.Aerodynamic forces are related to theair-body interactions while hydrodynamic forces to water-body interactions.In this thesis thehydrodynamic forces acting on the hull of the boat will be analyzed .The main objective isto determine the response of the vessel to heave and pitch motions in regular waves head seaat low forward speed.In order to obtain those motions some simplification are done.