HAYES— U. S. NAVY MV TYPE OF HYDROPHONE. 383 



The sounding equation, D = C ,-{- L tan ^, on the other hand, 

 would seem to predict that the depth of water (D) is determined 

 with greater accuracy as the water becomes more shallow, since the 

 value of the tangent varies less rapidly with variation of the angle as 

 the angle approaches zero. This does not hold true, however, for 

 the reason that the error in the determination of $ becomes abnor- 

 mally large as the value of this angle approaches zero and it results 

 from these considerations that depths of from 2 to 5 fathoms are 

 not determined with as great accuracy as depths from 10 to 20 

 fathoms if hydrophones of the type described are used. This type 

 is shown in the left-hand diagram of Fig. 7, where the line of the 

 receivers is horizontal and parallel with the ship's keel. 



5 H 5 /3/~~---_ M 



V "A-^r V ^-- 



\ '\^^^ \ 



/ 



\ 



\ / . \ / 



/ 





For sma// i^/i/es of "P (Shofhvr vvoter) fao'>s>9')30* so fhof a' moi^ be 

 measured w/th /ess error fhon s. 



Advantage df Inclined Mydrdphdne Line fdr Sounding 



Fig. 7. 



This weakness arises whenever the same hydrophone receivers 

 are used for determining both the bearing of vessels or shore signals 

 and also for taking soundings. It is readily removed if a separate 

 set of receivers is installed for sounding purposes only. These re- 

 ceivers are mounted in a vertical plane parallel to the keel and along 

 a line making an angle of about 30° with the surface, the forward 

 end of the line of the receivers being lower as is shown in the right- 

 Ijand diagram of Fig. 7. With such an arrangement of receivers 

 the sounding angle $ will be given by subtracting 30° plus the angle 

 given by the compensator from 180°, and the compensator will only 

 be required to determine angles between 60° and 150°. In this way 

 the most accurate part of the compensator scale is utilized for deter- 



