input was wired to the audio jack on the PFR recorder being used to monitor 

 the 12 kHz wide beam system. Range to the transponders was thus increased 

 to 6 miles. The 12 kHz return from the bottom finding pinger was also 

 strong. It was discovered that the duty cycle of the pinger could be ignored 

 because no interference was noted between the pinger and transponders. 



Ship and sentinel positions were determined using the equipment setup 

 illustrated in figure 19. The choice of transmit and receive frequencies 

 for the various transponders was dictated by the transmit and receive 

 frequencies of the functioning MAVA release. The ship's position was 

 determined by transmitting an 11 kHz ping to the transponders in the net 

 ("A","B",MAVA) . They in turn responded by transmitting pings of 9.5 kHz, 

 10.5 kHz and 10.0 kHz respectively. These signals were then decoded by 

 the AMF/EG&G 206A receiver. Conversion of the three round trip travel 

 times into horizontal ranges to each transponder permitted plotting the 

 ship's position at the intersection of the three radii. The sentinel posi- 

 tion was determined by transmitting a 9 kHz ping to the sentinel transponder 

 which in turn transmitted at 11 kHz. The sentinel transmit ping (11 kHz) was 

 then received by "A", "B", and MAVA which in turn transmitted at their 

 designated frequencies. Once again, these signals were decoded by the 

 AMF/EG&G 206A receiver which displayed the following four round trip times: 

 1) Ship-Sentinel-Ship; 2) Ship-Sentinel-"A"-Ship; 3) Ship-Sentinel-"B"-Ship; 

 4) Ship-Sentinel -MAVA-Ship. Having determined the travel times from the 

 ship to "A" (as measured using a direct interrogation at 11 kHz) and from 

 the ship to the sentinel, these may be subtracted from the overall round trip 

 time yielding the slant range between the sentinel and "A". Given the 

 vertical position of the sentinel, as determined by the difference between 

 the direct and bottom return from the pinger, the horizontal range from the 

 sentinel to "A" was calculated. This process was then repeated for the "B" 

 and MAVA transponders. The three radii were then plotted to intersect at 

 the sentinel position. 



VII, The Recovery Operation 



The operation commenced on the 8th of December when the still func- 

 tioning MAVA transponder was located. By the end of the day on the 10th 

 of December the transponder net had been deployed and its geometry accurately 

 determined. The major difficulty encountered during this phase was navi- 

 gation. Without Loran C, we were forced to dead reckon between satellite 

 fixes and occasionally got "lost". 



On December 11th, degrading weather conditions (30 knot winds) 

 forced a hold on launching the recovery array until midday. By 1830 hours 

 the sweepline array was in the water, but the pinger had quit working, the 

 line tension monitoring system was reading zero (line tension was actually 

 7500 lb) and the sweepline transponders were pinging at random! By 0930 

 the next morning (12 December) we had desensitized the sentinel transponder, 

 deactivated the anchor transponder, repaired the bad pinger, and fixed and 

 recalibrated the line tension monitoring system. At 1000 hours, while 

 lowering the array to the bottom, the line tension system went out again. It 

 was decided to proceed without a tension measurement and rely on the catenary 

 analysis to predict line tension. 



13 



