Eggers 



1,00 



Fig.Dl - Total "X-Y" method predic- 

 tion from Eggers' computer results 

 (ship with parabolic waterlines, 7g = 

 10.0, and 2X/L = 10.0) 



I thank the author for selecting the very specialized "X-Y" function to use 

 as a illustration of his computer results, and I take this opportunity to point out 

 that it is not necessary for this quantity to equal 100% of the theoretical wave 

 resistance for validity of the method to be established. This is because the 

 "X-Y" method also includes a "centerline wave term," R^ , which is not in- 

 cluded in the author's Fig. 2. Using wave elevation data from the same com- 

 puter program, kindly supplied to me by the author, I have made an estimate of 

 this term and have added it to the "X-Y" term for the location 2X/L = 10.0 as 

 shown in Fig. Dl. The centerline wave term R^ is drawn for convenience from 

 the top down, and is roughly linear with the distance 2Y/L off the centerline. 

 Similar lines can be drawn for the other locations. It can be seen that the addi- 

 tion of this term brings the method into almost exact agreement with the theory 

 at this section, assuming measurements to be taken at the distance 1.0 — 2Y/L ^ 

 2.5, the former limit being required by the need to exclude the local effect from 

 the measurements and the latter because the centerline wave term as calculated 

 is an approximation based on a plane wave which becomes inexact too far from 

 the centerline, and also because of tank wall effects. This dimension in the 

 case of all previous tests using this method was selected within these limits, 

 but I am of course happy to have a more rational basis for making this selection 

 in the future. 



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