If you think of trim actually, we know there is pressure acting, normal pressure acting on the ship surface, we have found out the axial component of that and we have said now that is equal to resistance, what about the vertical component? We have said the vertical component gives buoyancy. Now, I am moving the ship- that was in static condition when there was no axial component, only vertical component- now moving the ship the pressure distribution changes everywhere, we have said the horizontal component is equal to resistance, what about the vertical component, that will not remain same because pressures are different now.