Motion and Resistance of a Low-Waterplane Catamaran 



beneficial wave interference between struts and main-hulls. After 

 a number of computations, the following singularity distributions 

 for each demihull strut were chosen : 



Forebody 



Surface Source 



2 3 4 5 



m(x) = 9.4498x - 69. 5632x +189.4110x -213.4796x + 83. 5701x 



Surface Doublet 



3 4 



D(x) = 1. 1375 (x -.4) - 1. 1375 (x - .4) 



with . 4 < x < 1 



The doublet was in the x-direction. Singularity distributions 

 for the afterbody were such that a symmetrical strut was obtained. 

 The depth of these distributions was 0. 118. 



Model Experimental Results. The offsets of the effective 

 hull form were obtained in the same manner as in the case of Model 

 5266. In this case, it was decided to keep the demihull geometry the 

 same as that of its effective hull geometry for two purposes : first, 

 to be able to test a demihull alone without the complications of cam- 

 ber, and, second, to have a gross assessment as to the penalty of 

 having no camber. By comparing the theoretical and experimental 

 resistance results of a catamaran and a demihull, it might be possible 

 to estimate the added resistance due to displacement interference 

 effects. Figure 14 shows the lines of this model, and figure 15 

 gives the hull charactereistics of this design. 



Comparison Between Theoretical Wavemaking Resistance 

 Coefficient C w and Experimental Residual Resistance C r . The 

 theoretical predictions and experimental results are given in figure 

 16 . The C r curves are much higher than expected both for a 

 catamaran configuration and a single hull. In view of the good agree- 

 ment between C w and C r curves for Model 52 66, the cause of 

 the disagreement for this model is not clear. In view of this, addi- 

 tional tests with modified struts were carried out. 



Additional Results from One Demihull Tested Alone. It was 

 speculated that the blunt strut endings followed by rapid curvature 

 changes might have caused flow separation. If separation did occur, 

 the testing model would have been modified and would not have been 



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