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



® 7-63 



fathom curve and back again into Newport Harbor, give some idea 

 of the accuracy with which the MV hydrophone gives soundings 

 over a favorable sea-bottom. (This course is laid off on the chart 

 of Fig. lo.) Unfortunately the sounding machine broke down at 

 the start, so the comparison data is not as complete as that taken on 

 board the Breckinridge. The deep sea lead, however, was provided 

 with a sounding tube which operated on the Kelvin principle and 

 for depths beyond lo fathoms the soundings were taken from this 

 tube and not from the amount of line let out. 



It is to be noticed that the hydrophone sounding curve (repre- 

 sented by the heavy full line) agrees very closely with the curve 

 representing charted depths (light full line) except for the shoal 

 area near Block Island. Here, however, the agreement with the 

 soundings taken by the hand lead is almost perfect. The hand lead 

 soundings in this region were taken with great care and there is no 

 doubt in the minds of the experimenters but that the charted depths 

 are about 2 fathoms too small. 



The sounding tube seemed to function badly for depths beyond 

 50 or 60 fathoms and indicated little or no change for depths be- 

 yond 80 fathoms. At first it was suspected that the charted values 

 were in error at the greater depths but the fact that the hydrophone 

 soundings agreed closely with the charted depths and that the sup- 

 posed position of the Blakeley checked perfectly on the return trip 

 led, all concerned to the belief that the charted depths are correct 

 and that, on the whole, the soundings taken by the hydrophone are 

 more reliable than those given by either the sounding tube or the 

 chart. 



Conclusion, 



The MV hydrophone is the result of two years of intensive re- 

 search work carried out by the Navy. It was developed as an 

 instrument of warfare at a considerable cost and those best qualified 

 to make such estimates claim that this expenditure is but a small 

 per cent, of the saving to the Allied Powers which the hydrophone 

 affected during the period of the war. 



During the past year the Navy has discovered that the same 

 qualities that enabled the MV hydrophone to detect and accurately 



