TER OEPLECTORS 



Figure T-4. Boomer sound source sled. 



10 inches wide, and 10 inches high. If greater 

 power is desired, a .six-electrode assembly can 

 be made by fastening two three-electrode 

 frames together, side by side ; also, if maximum 

 power is required, a special nine-electrode 

 sparker frame is available. 



Instructions that follow are specifically for 

 the three-electrode frame; however, they are 

 applicable also to the six- and nine-electrode 

 assemblies : 



Step 1. Tighten all bolts that secure the elec- 

 trodes to the stainless steel frame. 



Step 2. Coat the electrode sockets with sili- 

 cone grease, snap the electrodes in jslace, and 

 wrap tlie socket and about 1 inch of the elec- 

 trode witli rubber tape to reduce the possibility 

 of tlie electrode separating from the socket. 



Step 3. Connect the power cable of the 

 sparker to the output socket of the triggered 

 capacitor bank (Mod 231) sound source in- 

 strumentation shown in figure T-5, allowing a 

 maximum of 2500 joules per electrode. 



Step 4. Lower the frame over the side and 

 tow 15 to 25 feet aft port with the power cable 

 snubbed to a cleat on the fantail. If the frame 

 fails to tow properly (6 to 10 feet beneath the 

 surface), attach two manila lines, one forward 

 and one aft on the frame and adjust until the 

 frame tows at a depth of 6 to 10 feet. 



3. Launching and Retrieving the Hydro- 

 phone Array. — Eitlier hydrophone array can be 

 used to receive either sound source. The hydro- 

 phone array ( 10 hydrophones, 10 feet in length) 

 is towed approximately 500 feet aft of the ship ; 

 the hydrophone array (10 hydrophones, 128 feet 

 in length) is towed approximately 1,800 feet aft 

 of the ship. Both arrays are launched and 

 retrieved by hand, and several (five to seven) 

 persons are required for the operation. 



These arrays, usually, attain their proper tow- 

 ing depth (6 to 10 feet) because of the buoyant 

 liquids contained in their acoustically trans- 

 parent vinyl plastic outer sheath; however, if 

 a depressor is necessary, it should be placed 50 

 to 100 feet forward of the hydrophones. 



The hydrophone array is connected to the 

 hydrophone tow cable with a joy plug, and the 

 array is lowered over the side while the ship 

 is underway. The cable is reeled off and payed 

 out by hand until the desired distance aft of the 

 ship is attained. The cable is snubbed around 

 a cleat on the aft starboard fantail during the 

 towing. 



4. Obtaining Seismic Profile Data. — When 

 the sound source and the hydrophone array have 

 been launched and are towing at 6 to 10 feet 

 beneath the surface, the system is ready to op- 

 erate. For satisfactory results, sound source in- 

 struments and receiving instruments should not 

 be supplied by the same power generators. 



Step 1. Connect the hydrophone cable to the 

 input of the amplifier, set the band pass filter to 

 70-150 cps for sparker source or 100-200 cps 

 for boomer somid source, connect the output 

 leads of the band pass filter to a recorder 

 (PGR, PESR, or PDR), and connect the re- 

 corder's trigger switch lead to the triggered ca- 

 pacitor bank (Mod 231). 



Step 2. Adjust the gain of the amplifier to 

 obtain a readable signal on the recorder; figure 

 T-6 presents an example of a good signal. An- 

 notate the strip chart at 30-minute intervals 

 with a time mark, the date, and the ship's name. 

 In addition, maintain a logbook with the above 

 information, all instrumentation control set- 

 tings, and any explanations pertinent to the 

 operation. 



Step 3. During seismic profile operations, the 

 sound source requires periodic mspections and 

 maintenance. Retrieve the boomer once each 12 

 hours and inspect the aluminum plates for 

 holes, check the area between the plates and 

 coil for small pieces of metal, and examine the 

 towing sled for broken parts or loose nuts. Re- 



T-3 



