1222 
-2- 
Type 18 has 12 inches of cordtex from the bung of one charge to the bung of tne other charge, 
corresponding to a distance which the detonation wave has to travel of 19 inches of cordtex and 
14 inches of primer and T.N.T. 
In Multiple Charge type 2 (see Figure 2) the two 14 lbs T.N.T. Charges are fixed by 
small cieces of wood with axes horizontal, with the orimer end of tne two charges oointing In 
the same direction and the crimer eno of the target charge nearer to the initiator charge. 
There Is 6 inches of water between the two charges and 6 inches of cordtex between tne bung of 
the target charge and the ena of tne initiator charge, corresponding to a aistance which the 
detonatlon wave has to travel of 5 inches of charye and 10 inches of cordtex, 
Multiple Charge type 1A is more efficient tnan Multiole Charges type 18 and 2. Trials 
were carried out on the latter two charges to clear up points of interest which arose. The 
charge type 1a is found to have a high efficiency within a cone of 50 degrees semi-vertical 
angle about the 0 degree direction as axis (throughout the reoort the 0 degree direction is the 
horizontal line from the centre of the initiator charge to the centre of the target charge and 
all directtons quoted are directions in the horizontal plane through the 0 deyree direction). 
within the cone the pressure oulses from the two constituent charges combine to form a Mach Wave. 
Charge type 1B was investljated because it was already known that the Mach wave from such a 
charge extended to the 9@ deyree direction at least. Theoretical consiaerations suggest that 
where the constituent charges detonate simultanecusly the Mach wave angle is centred about the 
90 degree direction, Multlole Charge type 2 was chosen as being one in which the detonat ions 
were nearly simultaneous, it being impossible to cut down the length of cordtex in the Tyoe 1 
Charges below 12 Inches without introducing right angle bends. 
Since the distance between the centre of gravity of the constituent charges in Type 1 is 
84 Inches as Compared with 15 Inches in Type 2? no comparison between ‘vertical" and ‘horizontal’ 
charges is possible. 
Experimental details. 
Preliminary trial. 
AS a preliminary trial the length of cordtex in Multiole Charge Type 1 was varied and 
the efficiency with each length of coratex measured by four piezo-electric pressure gauges. 
The gauges, with axes vertical and one side facing the cnarje were slung at the same depth as 
the charge, 7 ft. in Horsea Lake as follows (see Figure 3):- 
(1) Pear Gauge (crystal area 2 sides x & inches diameter) 15 ft. from the 
charge in the direction 0 degrees, 
(2) A thira size strio gauge (crystal area 2 sidas x 5 inches x 14 inches) 
30 ft. from the charye in the direction 30 deyrees. 
(3) A full size strio gauge (crystal area 2 sides x 18 inches x 14 inches) 
55 ft. from the charge in the direction 45 deyress. 
(4) A full size strip gauge 37 ft. from the charge in the direction 90 degrees. 
The gauye was placed at 90 degrees to give an aooroximate value for the time interval 
between the detonation of the initiator and target charges, the argument being that since the 
gauge is equidistant from the two charges the culses ‘from the initiator and target charges would 
travel to tne gauge in equal times and hence the time between the arrivals of the two oulses at 
the gauge is tne time lag between the detonations themselves. This argument is only 
approximately true because tne orcssure pulse from the target charge may travel in cart through 
water which Is already at a hign cressure due to the initiator charges Again the measurements 
snow that when the target charye detonates a small but finite time (e.3. 2 microsecmds) after 
the initiator charge the 90 degree yauge records not two but cne oulse only which on the above 
argument implies that the two charyes detonate simultaneously whereas in fact simultaneous 
detonation is not possible. This metnco of time interval measurement fails in such 
circumstances due to the formation of a Mach wave. 
The results of the oreliminary trial are given in Table 1 ana In Figures 6 ano 7, 
A normal 24 1b. T.N.T. Charge consisting cf two 14 1b. T.N.T. Charges strapped together was 
fired at regular intervals and Tapl< 1 gives the maximum oressure and momentum of the Multiple 
Charge 1 with lengths of cordtex varying from 8 inches to 50 inches given as percentages of the 
MAXIMUM seeee 
