In the previous reports, No. 2 and No. 3, the authors presented the methods for the bending calculation of deckhouse and superstructure, but in their calculations, the effect of openings in the wall of superstructure was not considered. In this paper, to investigate the effect of openings on the longitudinal stress distribution of superstructure, the effective cross sectional area and the effective moment of inertia of the superstructure were determined taking into consideration of the deformation of the openings, and using these, the experimental results were analysed.