EQUIPMENT AT MOUNTAIN LAKES 



87 



Figure 25. Determining the testing distance between 

 transducers. Rotator shown at far end of test area is 

 mounted on "H" type carriage. 



Figure 2fi. Typical test arrangement using turret type 

 carriage. Portable coupling amplifier in foreground. 



reflections. 1 ' The most common screens are thin- 

 walled watertight metal envelopes about 2 by 4 feet 

 by 1 inch containing a sheet of hard felt. Flanges 

 along the 2-foot edges permit the assembly of several 

 screens in multiple-unit configurations. Figure 27 

 shows a V assembly being placed in position to func- 

 tion as a surface screen, that is, to reduce surface 

 reflections from the region between a projector and 

 a hydrophone. Similar assemblies are sometimes 

 placed below the acoustic axis of transmission with 

 the V inverted to minimize bottom reflections. 



Special Facilities. Compressed air is generally 

 available from an outlet and special filter in the 

 transmission booth of pier 1. This installation is 

 primarily for charging the reservoirs of 4A- and 4B- 

 type low-frequency projectors. Other general uses 

 include cleaning and drying the less accessible parts 

 of miscellaneous gear with air blasts. 



A portable gear pump delivering about 10 gallons 

 per minute and driven by a reversible motor is pro- 

 vided for use on the piers. A long connecting shaft 

 allows the pump to be immersed in the lake, thus 

 providing a water supply free from air. The pump is 

 used for washing and debubbling test transducers 

 and for filling and emptying domes not provided 

 with drain plugs. 



An underwater lamp and a viewing device are 

 available for examining transducers and their rig- 

 ging in test positions. 



A portable box of wrenches, screwdrivers, pliers, 

 and other tools used for rigging is maintained at each 

 pier. A complete supply of rules, graduated steel 

 tapes, levels, and general marine hardware is avail- 

 able for measurements and rigging. 



Maintenance of Performance 



Safety Precautions. Units having dangerously high 

 voltages are equipped with safety switches which 

 must be opened before access to the unit is made. 

 This is accomplished by an interlocking mechanism, 

 which must be checked frequently for correct opera- 

 tion. 



b A general discussion of screens, from a theoretical stand- 

 point, is given in Chapter 4. 



Figure 27. Lowering the "V" screen into position lor re- 

 ducing surface reflections. 



