Chapter 3 — BEARINGS AND MOTION 



000 



270 



SUB H090 



TRUE PICTURE 



180 

 RELATIVE PICTURE 



Figure 3-7.— Effect of gyro failure. 



B 



71.4 



be heading for a target bearing 090° true, but 

 the target echo is presented at the top of the 

 scope. 



The effect of gyro failure is illustrated in 

 figure 3-7. Part A shows the scope with normal 

 gyro input. The submarine is located to the 

 right of center. The stern line is at 270° and 

 indicates that the ship is on course 090° true 

 and headed for the contact. 



With a gyro casualty, the stern line will 

 swing 90° counterclockwise. The entire video 

 presentation will change a like amount in the 

 same direction as shown in part B of the illus- 

 tration. To remain on target, the bearing cursor 

 must also be trained 90° counterclockwise. The 

 dials below the scopes in the illustration indicate 

 the direction in which the beau'ing cursor is 

 trained to maintain contact. 



CONVERTING TRUE AND RELATIVE 

 BEARINGS 



bearing is 029° and the ship's course is 027° 

 true, for instance, as in figure 3-8, you can see 

 that the true bearing of the target is 056°. The 

 true bearing is obtained by adding the ship's 

 course and the target's relative bearing. Thus, 

 by the formula we have: 



027°T + 029°R = 056°T. 



Now examine figure 3-9. The ship is on a 

 course of 180° true, and the target is at 251° 

 relative. Again, it is easy to determine true 

 target bearing by applying the formula as before: 



180°T + 251°R = 431°T. 



This time the bearing is greater than 360°. When 

 the answer exceeds 360°, you must subtract this 

 figure to obtain the correct answer. Thus: 



180°T + 251°R = 431°T - 360°T = 071°T. 



Even though you lose gyro input to the sonar, 

 you can easily determine the true bearing of 

 the target if you know your ship's course and 

 the relative bearing of the target. If the relative 



RULES FOR CONVERSION 



Certain rules are established for converting 

 true and relative bearings. After each rule is 



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