Pien and Lee 



DISCUSSION 



T. K. S. Murthy 



Portsmouth Polytechnic 

 Portsmouth, U. K. 



I have not had occasion so far to read the paper which Dr. 

 Pien and Dr. Lee have presented, but from the presentation and the 

 discussion I can see that they have used strip theory with two-dimen- 

 sional damping values and that they have also made the assumption 

 that the waves are not disturbed by the catamaran. These are perhaps 

 two shortcomings in the work but it is obvious from the talk I gave 

 this morning that if we put the parameter beta equals zero - we have 

 chosen four parameters - delta, beta, alpha and epsilon - if we put 

 beta relating to the cushion pressure equal to zero we get all the 

 results we require for a catamaran. 



In my treatment I did not start from the equations of motion, 

 as is normally done. I have not specifically used added mass and 

 damping values, but these are implicit in the equations. The strip 

 theory is always suspect, particularly at forward speeds, and it is 

 better not to use it. Although my theory is applicable only to the thin 

 hulls of the conventional catamaran, it can also be applied to circu- 

 lar cylinders well below the free surface, whatever the dimensions 

 might be, because then the wavemaking could be considered fairly 

 negligible. I would strongly recommend that Dr. Pien and Dr. Lee 

 use the method talked about this morning to see how it compares 

 with their results. We should be very glad to collaborate with them 

 in this respect and do some work at the University if required for 

 confirmation of their results. This is a different approach. It does 

 not make any explicit assumptions and we get the same results by a 

 different approach. I strongly recommend some sort of collaboration 

 between NSRDC and the University. 



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