Dynamic analysis of structures when partly or fully submerged in water has additional dynamic forces caused due to surrounding water. The motion of the fluid in contact with dynamic system gives rise to an effect which is equivalent to an increase in the apparent mass of the system. The determination of this added mass due to submergence in a fluid has been the subject of many analytical and experimental investigations (Stelson and Mavis (1957), Liaw and Chopra (1973)). Theoretical and experimental studies have shown that a system has a longer period of vibration and a higher damping when vibrating in water as compared to that in air (Clough(1960), Chandrasekaran et al. (1972)). This increase in the natural period of vibration of the system is due to an increase in the apparent mass of the system as a result of interaction between the structure and surrounding water. Experiments, though adequate enough for period estimation, cannot give the hydrodynamic pressure distribution. If the hydrodynamic pressure distribution can be known with accuracy, the resulting additional mass which will be moving with the structure can be evaluated.