Vassilopoulos and Mandel 



DISCUSSION B 



THE PITCH AND HEAVE OF TEN SHIPS OF DESTROYER- 

 PREDICTIONS COMPARED WITH MODEL TEST RESULTS 



COMPUTER PREDICTIONS COMPARED WITH MODEL TEST RESULTS 



Peter A. Gale 



Bureau of Ships 

 Washington, D.C. 



NOTES 



1. Regular wave model test results were collected for ten destroyer-like 

 ships. The data for five of the ships (F-K) were classified. By coincidence, 

 model test phase angle results were not available for these same five ships. 

 Due to the above, data sources, ship identifications and dimensions, body plans, 

 and phase angle comparisons are not presented for ships F-K. 



2. For ships, F and G the longitudinal gyradius of the model was not known. 

 In order to use the computer to predict the motions of these two ships, K0 was 

 assumed to be 0,25L for both. These facts make the comparisons presented for 

 ships F and G of dubious value. 



3. The hull dimensions and coefficients presented in the Table of Ship Par- 

 ticulars are those used for the computer motion calculations. In general they 

 also apply to the model test hull forms. In a few cases there are minor differ- 

 ences between the forms model tested and those used for the motion computa- 

 tions as, for example, when the model tested did not float on an even keel. Mo- 

 tion computations were always made for the even keel case. 



4. In the graphs, the circles connected by lines represent the computer 

 calculations. The model test results are represented by symbols other than 

 circles. Ship K was model tested in regular waves of several heights and all of 

 the test results are presented necessitating the use of a different ordinate than 

 used for the other plots. 



5. The following reports were the sources of the model test data for ships 

 A-E. 



a. For ships A and B: 



"An Experimental Study of the Effect of Extreme Variations in Pro- 

 portions and Form on Ship Model Behavior in Waves," by Numata and 

 Lewis, ETT Report No. 643, December 1957. 



368 



