611 



A METHOD OF DETERMINING THE DEPTH OF 



UNDERWATER EXPLOSIONS 



R. A. Shaw 



Marine Aircraft Experimental Establishment 

 Scotland 



December 1941 



Summary ^ 



A metnoo of aetemining the aeotti of fletonation ot a OomD excloOing under water from 

 measuremsnts of the distribution of velocity in the soray dome Is descrioeo. The methoa is 

 based on the assumot ion that the detonation wave aDoroximstes to a sound wave. This leaas tc 

 the relationshic that the initial velocity at each coint in the dome is inversely prooortional tc 

 the square cf its distance from the centre of detonation, so that the deoth of detonation can 

 De found from the ratios of the initi?.! velocities at different radii, Th? method has been 

 aoolle:: to th? annlysis of tests with dsoth Charges, and reasonably consistent results cbt^iinea. 



Introduction . 



When bombs are intended to be drccced into water, it is imoortant to know at what decth 

 detonation takes olace. 



A method of obtaining the oecth is described which oepsn^is on an analysis of the velocity 

 distribution in the scray dome wnjch aooear? on tni surface cf the water above the exolcding charge 

 immediately after detonation. 



Ths method depends on an aocroximat ion, which will have to be justified by results, but 

 as a methcc it has several marked advantages; standard bombs are used, the tests can be done 

 anywhere orovideo calm deep water is available, and the only equioment necessary is a cine camera 



ooeraled from a surface craft. 



Method . 



A tyoical examcle of the soray dome is shown in Figure- I'which t-s made uc of enlargements 

 from the cine film of a tfiSt with a oeoth charge. The growth of the same dome is shown graphically 

 in Figure 2, which gives th^ neijht of tne dom€ at various radii, plotted on a common time base. 



Tne assumotion made in the method is that, to a sufficient aooroximat ion, the initial 

 velocity of the spray M any ccint jn the ocme Is inversely oroDortional to the square of the 

 distance of that point from the centre of detonation. This is equivalent to saying that 



the ratio v/v indicates the deoth in terms of the radius 0=", at which the measurements have 

 been taken. In practice, the deoth is calculated t)y taking the average from several radii 



