In order to develop a practical prediction method for shipping water volume, load and pressure due to deck wetness, a model test was carried out for a domestic tanker in regular head seas. Shipping water height, load and pressure were measured at various ship speed and wave steepness. As for the occurrence of deck wetness, N. S. M. calculation of relative water height at bow gives a good estimation if the bow top height is reduced by considering the static swell up. A practical prediction method for shipping water height, load and pressure was proposed. The inputs of this method are relative water height at bow, pitching angle and bow vertical velocity, those can be calculated by strip theory and so on. The theory of “flood waves” was applied for evaluating the shipping water height from the relative water height at the bow and so on. This theory gives a better estimation of the water height distribution on deck than the conventional model of “dam collapsing” because it can include the effect of ship forward speed. On the shipping load and pressure, not only the static component but also the time derivative of the momentum of the shipping water were considered. It was clarified that the momentum component is important to estimate the peak of shipping water load and pressure. Having compared with measured data, it was confirmed that the combination of these two methods is practical enough for predicting shipping water load and pressure.