A New Appraisal of Strip Theory 



from the one presented in Ref. [5]. These studies have shown that in general 

 the Froude-Kriloff hypothesis (modified for Smith effect) supplemented by ap- 

 proximate corrections for the body-wave interference provide reasonable pre- 

 dictions of the excitation force and moment. The lack of severe dependence on 

 speed has also been noted in these studies. 



To supplement these correlations, the results of a preliminary analysis are 

 shown in Figs. 71 and 72. Theoretical forces and moments based on Jacobs' 

 formula, Eq. (40), have been compared with the experimental values given by 

 Gerritsma in Ref. [22] for an 8-foot, Series 60, Cg = 0.60 model. The ampli- 

 tudes of the heave exciting force compare more favorably than those of the 

 pitching moment, although there are some discrepancies at low wavelengths. 

 This finding seems to be in accord with Fay's statement [13] that the cross-flow 

 hypothesis will be more valid for wavelengths equal to or greater than the ship 

 length. Although results computed from Eq. (37) are not shown on Figs. 71 and 



15 



10 



10 



STRIP THEORY 



O • EXPERIMENT 



F = 0.20 





20 



STRIP THEORY 



O • EXPERIMENT 



30 



20 



- 10 



0.75 



.00 



1.25 

 X/L -' 



1.50 



.75 



Fig. 71 - Comparison of excitation force 

 and moment amplitudes 



343 



