The vertical bending moment in following sea to be calculated by Strip Methods has an important problem as obviously shown in the results of the international joint calculation under the Seakeeping Committee of I.T.T.C.
In this paper, for the first time, the following Transient Water Wave was adopted in experiments. As the results suggested, good data was obtained effectively, and the fact that Transient Water Wave is useful even in following sea conditions was proved. Next, a practical method of calculation taking into account three-dimensional correction is presented. By applying this method, experimental values of vertical bending moment in following waves at near -zero encounter frequency can be explained satisfactorily.