497 
NATURE OF THE PRESSURE IMPULSE PRODUCED BY THE DETONATION OF 
EXPLOSIVES UNDER WATER. AN INVESTIGATION BY THE PIEZO- 
ELECTRIC CATHODE-RAY OSCILLOGRAPH METHOD 
A, B. Wood 
November 1924 
* * * * *" * * * * * * 
Introduction 
Part A. Methods and Apparatus. 
Part 3. Experimental Results. 
Summary. 
OBJECTS OF THE EXPERIMENTS 
The experiments described in the report which follows are part of a series of practical and 
theoretical investigations. when complete these investigations will give data for determining the 
damage which will be done to a ship's structure by an underwater explosion without the necessity of 
carrying out large scale trials. 
A first step in determining the deformation which a structure will undergo, when subjected to 
to the effects of an explosion, is to: ascertain the magnitude of the forces due to the explosion, and 
in what manner these forces vary in the short interval of time during which they act. 
it is apparent, after slight consideration, that there are numerous factors which may affect the 
pressures generated at a point in the water, and their manner of variation, and which will therefore have 
to be taken into account in any attempt to predict the effects of an explosion under water, 
The chief factors are:- 
(a) The weight and nature of the charge. 
(b) The distance of the charge from the gauge (or point at which the measurements are made). 
(c) The distances of the charge and the gauge from the surface and bottom of the sea, 
and from bodies or surfaces which might modify the effect of the explosion. 
(d) The nature of the charge container (mine-case, tcrpedo warhead, etc.), the shape 
of the charge and the position of the point or paints of initiaticn. 
A sequence of different water—pressures due to an underwater explosion is completely described 
if we are able to state how long the abnormal pressures have endured and what was the excess of pressure 
over the normal at each instant during the time of operation of the effects of the explosion. it is 
therefore the object of this report to exhibit some of the relations between the shape of the curve 
showing water—pressures plotted against time, and the factors (a), (b), (c) and (d) above. 
There is one further point which should be mentioned. ultimately it is the effects of large 
explosions about which we desire information. The greater number of the experiments described in this 
report were made with small charges in the hope of discovering laws by which the effects of large 
explosions could be calculated. Larger charges were fired to check the laws derived from an examination 
of the results of experiments with small charges. The case of contact charges is outside the scope of 
this report. 
Results wee. 
