522 



The diaphragm xised in this type of gauge was steel or copper and 

 was 7 X 7 X ca. l/l6 in. thick. Before use, it was drilled with twelve 

 holes around the edge to correspond with the pin and cap screw holes 

 and all rovigh edges were smoothed off. The diaphragm vae then clamped 

 between the milled faces of the gauge plates. 



2. Method of Using the Ga\:tge 



Most shots were conducted in the fo3J.owlng manner. Four damage 

 gaxiges were mounted on a framework in the center of which was fixed the 

 explosive charge. The gauges all pointed toward the charge and were 

 spaced at approximately 90° intervals about the charge. 



Before clamping the diaphragm in place, a medium-bodied motor oil 

 (e.g., SAE-Uo) was applied with a paint brush to both of the milled 

 faces of each gauge to aid in keeping the gauge watertight. 



If the charge was sufficiently small (ca. l/2 lb.) the \rtiole rig 

 (frame, gauges and cheurge) could be lowered into the water from a boom 

 on the dock. In most cases, however, larger charges (up to 25 lbs.) 

 were used which necessitated working on a raft anchored out in the 

 harbor and suspending the rig after it had been lowered into the water 

 either from the raft or from a buoy attached by a horizontal line to 

 the raft. When the shot had been fired, the rig was raised to the 

 surface and new diaphragms insteilled in the gaiiges for the next shot. 

 Photographs of the larger rafts are shown in Figures 3 and ^ and the 

 smaller raft is shown in Figure 5. This pontoon-floated raft is particu- 

 larly convenient for this type of work. It is rectangvilar in shape 

 (23 ft. X 28 ft.) vith a 13 ft. X 16 ft. opening in the center. One end 

 has a 12 ft. x 23 ft. apron for a work space and the other end has a 

 gangway which can be removed for floating gear out of the center away 

 from the raft. An overhead quadrupod with cables to a winch permits 

 lowering and raising gear. When the raft is anchored in a current with 

 the open end down stream the gauges and gear can be lowered omtil they 

 are supported by a floating buoy and then the biioy and gear floated 

 down stream to a safe distance for firing the chsirge. 



Most of the charges used were cast in cylindrical cardboard or, , 

 tin can containers, and were boostered with pressed tetryl pellets.—/ 

 The booster was usually half -submerged in the explosive. The tetryl 

 pellets were initiated by a DuPont No. 8 electric detonator set into a 

 small well provided in the top pellet. Putty placed around the 

 detonator and tetryl waterproofed the latter sviff iciently up to depths 

 of iiO ft. 



3. Diaphragm Materials 



Both copper and hot-rolled steel were used as diaphragm materials. 

 The copper was annealed until it was dead- soft before \xse±/ . The steel 



it/ Philip Newmark and Ernest Patterson, OSRD Report No. 6259, HDRC 

 Report No. A-38I. 



