Chapter 3 — BEARINGS AND MOTION 



but remember that the finest equipment will 

 always need a competent operator. 



Range 



The distance from the sound source to the 

 target is called range. In sonar, range always 

 is expressed in yards. With modern sonar equip- 

 ment, range detection varies from less than 

 100 yards to thousands of yards. Ranges can be 

 measured to an accuracy of 1 percent of the 

 range scale in use. To achieve this accuracy 

 you must have up-to-date laiowledge of water 

 conditions and be able to make adjustments to 

 the equipment to compensate for variations in 

 the velocity of sound. 



Range is reported in thousands and hundreds 

 of yards. Some sample ranges, and the manner 

 in which they are reported, are listed here for 

 your information. 



3000 — "Range three thousand, closing." 

 2500 — "Range two five hundred." 

 1750 — "Range one seven five zero." 

 1100 — "Range one one hundred." 

 1000— "Range one thousand." 



800— "Range eight hundred." 



660 — "Range six six zero." 



150 — "Range one five zero." 



400 — "Range four hundred, opening." 



It should be noted that the word "yards" is 

 never included in a report, because ranges 

 always are given in yards. 



One range report by itself is insufficient to 

 conduct an attaclc, although such information as 

 whether the range is opening, closing, or constant 

 is of vital significance. A succession of both 

 bearing and range reports is required to deter- 

 mine target location and motion. 



SONAR CONTACT. BEARING 130° 



\*ll"/ 



SONAR CONTACT, BEARING 045° 



\|l|l// 



SONAR CONTACT. BEARINC 230° 



71.3 



Figure 3-1. — True bearings are independent of ship's head. 



21 



