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



mining depths and the determination then becomes progressively 

 more accurate as the water becomes shallower. 



The addition of a separate line of receivers does not complicate 

 or materially increase the cost of the installation, since by means of 

 a multiple-pole switch the same compensator can be used on all the 

 receiver lines. The electrical compensator is provided with such a 

 switch. 



Another method of reducing the sounding error in shoal water, 

 which is applicable to larger vessels, is as follows: If an artificial 

 sound-source is placed near the center of the vessel, as shown at (S) 

 in Fig. 3, it is evident that accurate shoal soundings can be taken 

 without the addition of a line of receivers inclined to the horizontal. 

 The reflected sound from this source does not approach parallelism 

 with the line of receivers except for extremely shallow water. With 

 such an arrangement an operator in taking deep soundings will make 

 use of the stern sound-source (the propeller), while for soundings 

 in shallow water he will utilize the centrally located sound-source. 



It is evident, from a consideration of the sounding equation, that 

 the error in the determination of the depth (D) resulting from the 

 error in the determination of the sounding angle $ will become ab- 

 normal when the depth is sufficiently great to cause this angle to 

 approach 90°, since the value of the tangent then varies rapidly with 

 change of angle. This weakness can be partially overcome by sepa- 

 rating the sound-source and the hydrophone as far as possible. 

 When the hydrophone and the sound-source are placed in opposite 

 ends of the vessel, reliable soundings are given for depths as great 

 as three times the length of the vessel. 



Graphical Representation of Errors Introduced by Incorrect 

 Determination of Sounding Angle. 



In order that the nature and magnitude of the errors in sounding, 

 due to incorrect determination of the sounding angle $, may be more 

 clearly understood, these determining factors will be illustrated 

 graphically. 



In Fig. 8, the full line in the center of the shaded area gives the 

 relation between depth and sounding angle $ when the sounding 

 equation 



