Wood is a material for which strength and elasticity vary greatly in relation to grain direction. To build wooden structures such as ships (which suffer from severe simultaneous bending and shear stresses), combining plankings of several directions has been found to be effective in providing inplane stiffness. These patterns are called diagonal systems of planking and were the subject of intense research during the 1950s'. Diagonal systems of planking made it possible to build much lighter and stronger wooden ships than those which had been built of only longitudinal plankings. Several problems remained unresolved by the earlier research projects : (1) There was no method to determine the complicated stress distribution of shell plankings. (2) There was no method to determine the reaction forces of joints. (3) Breaking stresses and modes of failure of planking were not well understood. The purpose of this project was to develop a method to analyze these aspects of wooden ship structures. Strength tests of shell structures were conducted by full scale partial models to investigate static behavior. The shell stiffness was investigated by a detailed FEM analysis of the shell. Axial stresses of each layer were analyzed for a whole ship FEM model using the unidirectional stiffness plate method. Then the detailed FEM analysis of the shell was conducted again to investigate local planking stresses and joint reaction forces. Breaking tests of the shell were also conducted to investigate breaking strength. Its failure mechanism was also discussed.