Pien and Lee 



of each demihull was obtained in two steps. In the first step, an effec- 

 tive hull form was derived from its singularity distribution bv the 

 method of double -model or zero-Froude-number technique. Further 

 simplification was introduced here by obtaining strut and main-hull 

 geometries separately. A load waterline for the strut was computed 

 from the strut singularities alone, and all the other waterlines were 

 the same as the load waterline. The main-hull geometry was obtai- 

 ned by tracing a streamline generated by the line source points in an 

 infinite medium. Then the strut and main-hull were joined together 

 with the proper fillet. In the second step, the demihull geometry was 

 computed from its effective hull form, and the singularity distribu- 

 tion of the other demihull properly located. Due to the small width 

 of the strut as compared with the flow curvature induced by the other 

 demihull, the load waterplane was cambered by computing the dis- 

 tortion of its centerline. To maintain the wall sidedness of the strut, 

 this camberline was used at all the depths. Furthermore, it was also 

 used to camber the submerged main-hull. 



For the purpose of internal functional arrangement and twin- 

 screw propulsion arrangement, the main-hull cross sections were 

 changed gradually from circular to elliptical sections, and a beaver- 

 tail was formed at the stern. To increase propeller submergence, 

 the tail end was slightly bent downward. Figure 12 shows the lines 

 of this model, and figure 13 gives the hull characteristics. 



A 1 6-ft model was built and tested for resistance and powe- 

 ring. The C r values were also plotted in figure 11 for compari- 

 son. 



Second Design Example - Model 5276. 



Singularity Distributions and Theoretical Wavemaking 

 Resitance. This design represents a 4000-ton, 30-knot ship. The 

 singularity distribution for each main-hull was chosen to be the same 

 as that of Model 5266. However, the main-hull geometry was kept 

 as a body of revolution. The operating Froude number was much 

 higher than that of Model 5266. Struts were redesigned to give better 

 performance at operating condition. 



At low Froude number, it is possible to achieve great 

 beneficial wave interference between struts and main-hulls. The 

 theoretical wavemaking resistance of a SWATHS way have lower 

 wavemaking resistance with than without struts, despite the added 

 strut-displacement volumes, as for Model 5266. At high Froude 

 number beyond the last hump, it is difficult to achieve such great 



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