Pien and Lee 



INTRODUCTION 



There are many types of naval ships which are volume - 

 limited. In such cases, the proposition of using a catamaran hull con- 

 figuration becomes very attractive because of its large deck area. A 

 conventional catamaran, however, was found to have some bad mo- 

 tion characteristics and cannot offer a stable platform in heavy seas. 

 Since the sea-excited ship motions can be reduced by submerging the 

 hull, a small -waterplane -area -twin-hull -ship (SWATHS) has become 

 a subject of great interest. 



To explore the potential advantages of a SWATHS , a few 

 experimental models were developed and tested for resistance as well 

 as for motions. The expected favorable motion characteristics were 

 generally confirmed. However, the resistance level was found to be 

 unusually high, and the power requirement was much higher than ex- 

 pected. The percentage of structural weight to total weight of a SWATHS 

 is also expected to be high. This, coupled with large machinery and 

 fuel weights, greatly restricts its payload. 



Before building a SWATHS which can accommodate a rea- 

 sonable payload, it is necessary to reduce the power requirement by 

 controlling the hull resistance, and to reduce the structural weight by 

 controlling the hydrodynamic loading on the hull structure. Since the 

 hydrodynamic loading depends upon the relative motions between the 

 hull and the surrounding water, it is essential to control the ship mo- 

 tions in such a way that the hydrodynamic loading is minimized. 



In attempt to solve this problem, an investigation of cata- 

 maran hydrodynamics was undertaken at the Naval Ship Research and 

 Development Center. Research efforts in catamaran motions were 

 made by the Ship Dynamics Division, while parallel efforts in cata- 

 maran resistance were made by the Ship Powering Division. Since 

 the development of a successful catamaran design is contingent upon 

 solving the motion and resistance problems simultaneously, the re- 

 sults of these efforts were incorporated, and are presented here as 

 a single contribution. 



This paper consists of two essentially independent parts 

 written by two different authors; the first part by Lee, and the second 

 part by Pien. In dealing with the motion problem, it was necessary 

 to carry the theoretical work beyond that of solving the motion pro- 

 blem of a single hull. Since this additional theoretical work has not 

 previously been published, it is discussed here in its entirety. 



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