method that concerns safety. When the hy- 

 drophone is deployed from a small boat, it 

 adds an element of risk, as well as further 

 inaccuracies. In this context, reference is 

 made to the DS-2000 incident in Chapter 15 

 wherein the small boat, support ship and 

 submersible all became separated with the 

 onset of inclement weather. 



Pinger/Transponder (Sub) — Hydrophone/ 

 Interrogator (Surf): 



The system described above requires the 

 operator to actively participate in determin- 

 ing the vehicle's horizontal distance from the 

 surface ship. First, he must respond with a 

 "Mark" of his own so that the surface ship 

 can compute slant range. Second, he must 

 provide his depth which is also a necessary 

 factor in slant range computations. A system 

 designed for BEN FRANKLIN's 30-day drift 

 provided all the necessary values with noth- 

 ing required on the part of the submersible's 

 operator. The system, designed by Martin 

 Fagot of the Naval Oceanographic Office, is 

 not necessarily the ultimate in surface track- 

 ing, but it is presented because it worked as 

 designed for 30 days. Such reliability is rare 

 in deep submergence. 



The tracking system, described by Fagot 

 and Merrifield (22), is shown in block dia- 

 gram in Figure 10.17. The submersible's com- 

 ponents consist of two independent subsys- 

 tems: A pinger and a transponder. The sup- 

 port ship's components consist of a line hy- 

 drophone, two transducers, a graphic re- 

 corder and speaker, an oscilloscope and asso- 

 ciated electronics. 



Pinger Subsystem — The pinger (General Time 

 Model No. 0B04A) is a self-powered acoustic 

 generator that emits a 4-kHz pulse at a 

 precise periodic rate of 1 pulse per 2 seconds. 

 Every primary pulse, 10 ms in length, is 

 followed by a secondary pulse, 2 ms in 

 length. The pulse separation is pressure de- 

 pendent and varies linearly from 20 to 400 

 milliseconds for pressures between psi and 

 5,000 psi. The battery pack, a 12-volt magne- 

 sium dry cell, provides a signaling life of 2 

 months for primary and secondary pulse 

 transmission. 



The characteristics of the directional hy- 

 drophone (Weston - DT-171A) used to receive 

 the pinger signal are as follows: Frequency 

 range of 500 to 20,000 Hz; open circuit volt- 



age sensitivity of 84 db below 1 volt per 

 microbar; directional beam pattern in the 

 horizontal plane, approximately 12 degrees 

 at 3 db down for a 4-kHz signal; and a front 

 to back sensitivity of 10 db as used in this 

 operation. When information concerning the 

 relative bearing to BEN FRANKLIN was not 

 required, an omnidirectional hydrophone 

 (Atlantic Research LC-50) was used instead 

 of the directional transducer. 



The output of each hydrophone was iso- 

 lated, filtered and amplified before being dis- 

 played on the graphic recorder. The recorder 

 was a Gifft model GDR-IG-19-T. Since scale 

 was 200 fathoms for 2-way travel time, the 

 distance represented by one sweep was 400 

 fathoms or 2,400 feet across the record. With 



4-kHz 

 RECEIVER 



n-^' 



GRAPHIC 

 RECORDER 



MANUAL 

 TRIGGER 



IS-kHz 

 TRANSMITTER 



16kHz 

 RECEIVER 



^ 



U LC 60 



lATL. RES.) 



SP 76 CT 

 (STRA2A) 



t6-kHz TRANSPONDER 



n 



4-kHz PINGER 

 (GENERAL TiMe) 



Q 



Fig. 10.17 Tracking system block diagram. 



501 



