SUMMARY AND CONCLUSIONS 



This report presents the application of the unified slender-body theory to 

 predict the motion of SWATH ships in head seas. At zero speed, the computed results 

 for a twin ellipsoid show overall improvement in the hydrodynamic forces and motions 

 compared with three-dimensional theory. For SWATH ships with high forward speed in 

 head seas and in following seas, there is some improvement in the added-mass and 

 damping coefficients compared with two-dimensional results, but for the exciting 

 forces and motions the same improvement is not expected. In following seas, the 

 motions of SWATH 6A show unexpected large peak values at small encounter frequencies. 

 The motion results of SWATH 6D agree very well with the experiments. 



From the present study, the following conclusions have been drawn: 



1. The slender-body theory improves the two-dimensional predictions of added- 

 mass and damping coefficients. The same improvement has been shown for surface 

 ships in Reference 5. 



2. The application of the slender-body theory for the prediction of exciting 

 forces has not been entirely successful. Further investigation is necessary in this 

 area. 



3. Except for the pitch motion of SWATH 6D in following seas, the computed 

 motions have not been significantly improved by the application of the slender-body 

 theory. When the sectional interaction terms are solved with the sectional source 

 strength of the slender-body theory, they are strongly influenced by strip theory in 

 head seas. Further investigation of these interactions is therefore warranted and 

 is necessary to the final development of the slender-body theory. 



ACKNOWLEDGMENT 

 The author gratefully acknowledges the support of Ms. M.D. Ochi, Dr. D.D. Moran, 

 and Mr. V. Monacella. 



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