Pi en and Lee 



forms are the same in a straight uniform flow, the design of an 

 effective hull form is equivalent to the design of a monohull. There- 

 fore, the concept of an effective hull form enables us to link together 

 the design problems of a single hull and a catamaran. This link is 

 an important step in the future development of catamaran technology. 

 With this link, it becomes possible to utilize all the knowledge and 

 information of single hull form design to the design of catamaran 

 hull forms. 



In designing a single hull form, there are two possible 

 approaches. One is the empirical approach, based on model series 

 work and successful ships built in the past. The other approach is 

 theoretical, the essential foundation of which is the wavemaking- 

 resistance theory. With the first approach, many good hull forms 

 have been developed. However, since it is not possible to know what 

 makes good hull forms, this approach is very difficult when design- 

 ing unusual hull forms for which there is very little available infor- 

 mation. On the other hand, due to the oversimplification of a theory, 

 the second approach cannot always produce satisfactory results. 

 Perhaps the most rewarding approach would be a combination of the 

 two and a great deal of intuition. At this point, we shall presume 

 that a good monohull can be developed one way or another, so we 

 shall not discuss the design of a single hull form further, except to 

 make a few remarks pertinent to demihull design. 



The attractive feature of a catamaran hull configuration, as 

 far as wavemaking resistance is concerned, is the added freedom in 

 the displacement-volume distribution. In the case of a monohull, the 

 required transverse stability limits the freedom of the displacement- 

 volume distribution in the vertical direction. The benefit of wave 

 cancellation can mainly be achieved by the proper longitudinal distri- 

 bution of the displacement-volume. In the case of a catamaran, the 

 transverse stability does not depend solely on the waterplane area of 

 each demihull. Hence, we can have more freedom in distributing the 

 displacement-volume in the vertical direction. It then becomes pos- 

 sible to have cancellation between waves produced by displacement 

 volume at various depths. In the case of a SWATHS , for ins- 

 tance, it is possible to have wave cancellation between a strut and a 

 submerged body. Since the distance between two demihulls can be 

 varied to a certain extent, another freedom of displacement-volume 

 distribution is obtained. As a result, a far greater degree of wave 

 cancellation is possible for a catamaran hull configuration than for 

 a monohull. In designing an effective hull form for a demihull, the 

 advantage of greater wave cancellation should be achieved. 



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