Chapter 7 — BASIC FIRE CONTROL 



SIGNAL 



ECHO 



STERN-ON 







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BOW 



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51.31(71) 



Figure 7-21. — Direct stern traces. 



51.31(71)A 



Figure 7-22. — Bow aspect traces. 



As you can see, part 1 returns to the trans- 

 ducer sooner than part 4, hence the echo is 

 recorded as a long trace. Because the trace is 

 drawn out, it is not as clear as a beam trace. 

 The ends are not clearly defined. At long range 

 the trace may be weak, but you can distinguish 

 it by the low doppler that accompanies it. 



If you have a stern-on target, the trace is 

 similar to a quarter trace. (See fig. 7-21.) On 

 a stern target, however, some of the echo re- 

 turns from the wake, some from the stern, some 

 from the conning tower, and some possibly from 

 the bow. This characteristic tends to make the 

 echo even longer than the quarter target. It is 

 not as solid as the quarter trace, but is quite 

 long. 



Stern traces also are irregular, and they 

 may vary in shape and length from echo to echo. 

 If the target is moving, doppler is down and the 

 left edge of the trace may be particularly irregular 

 because of the wake. 



The bow target traces, shown in figure 7-22, 

 are longer than beam traces. The portion of the 

 sound pulse that hits the bow returns ahead of 

 the part that hits the stern. The resulting echo 

 is lengthened. Doppler from a moving bow aspect 

 target is up. 



If the submarine is coming directly toward 

 your sound pulse, the trace is direct-bow, as it 

 appears in figure 7-23. Again, the trace is long, 

 because the echoes are returning at different 



ranges from various parts of the submarine. 

 The traces may be very weak until you are at 

 short range, when they begin to appear more 

 clearly. Because of the wake effect, direct-bow 

 traces are fairly irregular, especially at the 

 right edge. But the wake is not as prominent as 



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SIGNA 



ECHO 



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51.31(71)B 

 Figure 7-23. — Direct bow aspect traces. 



129 



