High speed ships like TSL (Techno Super Liner) have been developed recently for realization of modal-shift of transportation in Japan. The hull surfaces of these high speed ships are in contact with a rapid flow of water. These panels are so thin for light weight that the possibility of dynamic instability such as panel flutter phenomenon should be studied. The purpose of the present study is to investigate the possibility of dynamic instability of the outer panels of the ships. Finite element approach for plates and boundary element approach for surrounding fluid are used for the analysis of the fluid-structure interaction problem. The numerical code ISAP-TSL developed is used for investigation of the effect of mass ratio, boundary conditions and plate shape on the critical speed of flow and the reduction of natural frequencies. Moreover the difference between the dynamic characteristics of a plate and those of a continuous plate is discussed from the numerical results as well.