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



ascertain the corresponding limits of error as a function of the depth 

 by plotting the curves represented by the equation : 



d ± 0.2 

 D (fathoms) = i -|- 22.6 tan cos"^ — q~~q~' 



taking for the binaural arm (C) its value 28.98 inches in air (the 

 water path is 126 inches) and for the variable (d) the net compen- 

 sation of the line corresponding to various values of the sounding 

 angle <^. 



These curves have been drawn, one on either side of the true 

 sounding curve. Due to this personal error in determining <E>, the 

 maximum limits of which are set as ±0.2 air inches, it is evident 

 that a given sounding is liable to fall anywhere within the shaded 

 area bounded by these two curves. It is to be noticed that this area 

 widens in a vertical direction at both ends of the curve, i.e., the error 

 for very shallow and for great depths is greater than for inter- 

 mediate depths. The hydrophone installation in question has the 

 receivers installed along a horizontal line parallel to the ship's keel,. 

 as shown in the left-hand diagram of Fig. 7. 



In Fig. 9 the maximum error is plotted against depth as abscisssfr 

 and shows how the error is reduced for small depths when the line 

 of receivers is inclined to the ship's keel. The full line curve shows 

 the maximum error for various depths when the line of receivers is 

 parallel to the center line of the ship. The error increases rapidly 

 for depths below 10 fathoms. The broken line curve made of long- 

 dashes gives the maximum error when the line of receivers is inclined 

 30° to the horizontal in the manner shown in the right-hand diagram 

 of Fig. 7. Here the error at great depths is not materially increased. 

 The third curve gives the error when the line of receivers is inclined 

 60°. This arrangement further reduces the errors slightly in shallow 

 depths but clearly at the expense of increasing it considerably at 

 greater depths. 



It has been found that best results are given when the line of 

 receivers is inclined about 30° to the keel. Such an arrangement 

 reduces the error in shallow water sufficiently for all practical pur- 

 poses and at the same time does not materially increase the error for 

 greater depths. 



