Data of the transient transverse stresses during slamming obtained from sea tests showed that the transverse strength of a torpedo boat was considerably affected by the longitudinals, because the longitudinals were parts of strength members to resist the impact loads upon slamming another words, the external forces were transmitted to bottom longitudinals upon slamming immediately.
In order to calculate the reasonable transverse strength in the above case, several assumptions are introduced as follows :
1) Statical water pressure is substituted for the impact loads during slamming.
2) Statical water pressure is equally distributed over the all area of bottom shell bounded between two neighbouring transverse bulkheads along the lengthwise direction and extending transversely from the center girder to the lower chain,
3) By taking resistance of longitudinals into consideration for the transverse strength, so-called three dimensional analyses are basically applied, which were already introduced by Nishimura in the case of having deadrise.
4) A stiffened plate, which is composed of both stiffened bottom and side shells, is simply supported at two neighbouring transverse bulkheads, the edge of the side shell and clamped at the center girder.
In this paper, based upon the assumptions as above, the distribution of transverse moments and stresses are obtained by use of digital computer and compared with the results of conventional method used so far, so-called two-dimensional analyses, assuming two or three unknown forces to resist external pressure. By the above comparison the magnitudes of unknowns are determined and reversely, if these determined unknowns are applied, the two-dimensional analyses will again become an useful method to get an estimation of transverse strength at the stage of initial design. In order to get the correlation between the calculated results obtained as above and the data of sea tests during slamming, the equivalent statical pressure is first obtained from test data by making the magnitudes of calculated and experimental results equal to each other, and second the ratio of the equivalent statical pressure and the slam pressure corresponding to each boat's speed. The mean effect of variable pressures on the transverse stress, therefore, is given by the ratio determined as above, although the maximum and the distribution of pressure during slamming are always changing from time to time.