22 



SHOR 



[chap, 2 



0.045 - 



C.OZb 





0.025 



0.015 



0.005 



200 300 



Frequency in sec' lb' 



400 



500 



Fig. 1. Low-frequency part of the Fourier energy spectiuui of an explosion at 500-ft 

 depth. (After Raitt, 1952.) 



slowly moving ship can reach a safe distance away. The damaging effects are 

 accentuated in shallow w^ater, and the larger charges must often be fired at 

 greater depths than is desirable. At ranges short of that at which the first 

 refracted wave is detected, a series of small charges is frequently fired to get a 

 w'ide-angle reflection profile ; in this case the amount of energy is usually more 

 than adequate, even with quite small charges, and efficiency is sacrificed so as 

 to obtain a less complex arrival by firing the charges so near the surface that 



.E 200 - 



250 



300 



Charge weight in lb 



Fig. 2. Optimum charge depth and frequency as functions of charge weight. (After 

 Raitt, 1952.) 



