MOTION AND RESISTANCE OF A 

 LOW-WATERPLANE CATAMARAN 



P. C. Pien andC.M. Lee 



Naval Ship Research and Development Center 

 Bethesda s Maryland; U.S.A. 



ABSTRACT 



The unusually large, useful deck area is the advan- 

 tage normally associated with catamarans. In addi- 

 tion, small- waterplane-area- twin- hull-ship (SWATHS) 

 can exhibit good seaworthiness characteristics in 

 rough seas but at the expense of high powering re- 

 quirements due to the large wetted hull surface. A 

 well-balanced design of sucha craft must be the re- 

 sult of a compromise among motion, powering, and 

 structural weight considerations. In this paper, how- 

 ever, only the hydrodynamic aspect of the design is 

 discussed. It consists of two parts. The first part 

 deals with ship motion, while the second part deals 

 with resistance. 



In the first part, a theoretical method of predicting 

 the motion and hydrodynamic loads of catamarans in 

 a seaway is given. Based on theoretical analysis, 

 tolerable limits onhull characteristics are determin- 

 ed to ensure the desired motion characteristics. In 

 the second part, a set of lines is developed within 

 these limits such that the powering requirement is 

 an optimum. This is done theoretically, based on 

 existing wavemaking -resistance theory. Finally, a 

 design example is given to show how hydrodynamic 

 theories are used in designing a SWATHS. 



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