Vassilopoulos and Mandel 



10 - 



5 - 



15 



10 



5 - 



STRIP THEORY 



O • EXPERIMENT 



F=0.30 



30 



- 20 



STRIP THEORY 



O • EXPERIMENT 



10 



0.75 



1.00 



1.25 

 X/L- 



1.50 



1.75 



Fig. 72 - Comparison of excitation force 

 and moment amplitudes 



72, as previously noted, it is expected that these expressions will not yield an- 

 swers significantly different from Jacobs' Eq. (40). 



The discrepancies which are brought about by assuming that the body and 

 wave do not interfere need also to be examined. Grim's [52] theoretical work, 

 supplemented by Spens' [53] experimental work point out the considerable de- 

 crease in wave elevation as the wave passes along the ship length as well as the 

 presence of a bow-induced wave. There is no doubt that such interference ef- 

 fects, especially in astern seas [53], will sensibly modify the theoretical exciting 

 force and especially the pitching moment, which, at present, seem to be over- 

 estimated. It is not yet known whether a convenient correction may be applied 

 in Eq, (37) to allow for this discrepancy, but the matter will be considered more 

 carefully in the future. 



The diffraction problem has also been investigated more recently by Neu- 

 mann [54] on the basis of Haskind's theory. He presents a remarkably simple 



344 



