The authors tried the investigations on the freeboard according to “The 1966 International Conference on Load Lines” from the viewpoint of deck wetness. The long-term predictions of vertical ship motion relative to the wave surface were made for various type hull forms. Amplitudes of relative motion at the longitudinal locations along the ship length were predicted with constant exceeding probabilities on the North Atlantic Ocean. The results were compared with the freeboards regulated by the 1966 Conference.