Whenever a body moves in fluid there is a pressure force which develops around the body and that is normal to the body surface; we have seen if the fluid was non viscous and completely submerged, then the forward components of pressure would, the axial component of pressure in the forward part of the ship would be equal and opposite to the axial component of the pressure forces on the half body, so they will cancel each other and body will experience no resistance to forward motion. But as the body comes up to the surface the pressure developed around the body generates waves, and the wave generation is a phenomenon due to the existence of, existence of a free surface between air and water and effect of gravity- all water waves are gravity based phenomena and they are basically created because a constant atmospheric pressure has to be maintained on the water surface by physical law.