This thesis presents a technique for predicting the coupled heave and pitch motions of SWATH vessels in the time domain. The emphasis is on completing the essential foundation work required for developing a fully comprehensive, non-linear time domain model. A procedure for solving the coupled motion equations is developed for linear motions and then validated using predictions obtained from equivalent frequency domain analysis. Hydrodynamic quantities are calculated using a two dimensional strip theory method which involves solving source distribution boundary value conditions using the Frank Close-Fit technique. The methods employed for introducing some nonlinear effects caused by the time dependency of motion coefficients and wave exciting forces and moments are described. Results from a computer program written to perform the time domain calculations are used to illustrate the non-linear phenomena and to demonstrate the improved correlation with model test data that can be achieved using non-linear time domain analysis. Further development work is proposed. The influence of motion control fins and the occurrence of cross-structure slamming require careful consideration in SWATH ship design. Suitable approaches to introducing these non-linear effects into the simulation are suggested.
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