CHAP. XX.] METHOD OF SHIP SOUNDING 423 



The other end of the fore and after, 100 fathoms long, is 

 rove through leading blocks on the lower boom and at the 

 masthead, and secm-ed to the sounding winch, on which it is 

 reeled up. The other end of the depth-Hne is rove through a 

 leading block on the sounding spar, through another block on a 

 davit placed a short distance before or abaft the sounding spar, 

 thi'ough a block shackled to a counterpoise 112-pound lead, 

 through a block on the submarine sentry davit, placed as 

 most convenient, and reeled up on the submarine sentry 

 winch. 



The leading blocks on the lower boom and sounding spar 

 should project at about equal distances from the fore and aft 

 Hne of the ship. 



The general arrangement is shown in Fig. 89. 



In depths exceeding 20 fathoms, and at a speed of 3| knots, 

 it is necessary to heave the lead up to the lower boom ;in lesser 

 depths it need not be hauled so far forward. 



The lead being hove sufficiently forward to "let go," the 

 winch is revolved rapidly in the direction of " heaving out "; 

 the leadsman, assisted by the action of the counterpoise lead, 

 gathers in the slack of the depth-line, and calls the depth as the 

 lead, resting on the bottom, passes him with the depth-Une 

 up and down and taut. 



The effect of the counterpoise is to make the working of the 

 depth-line practically automatic. 



It is necessary, when the depths change much on a hne of 

 soundings, to adjust the position of the counterf)oise accord- 

 ingly ; this is easily and quicldy done by means of the submarine 

 sentry winch, on which the depth-line is reeled up for that 

 purpose. 



In the Research, with no screw propeller to consi ler, the 

 counterpoise hangs over the stern; in a screw vessel it would 

 probably be desirable to take the counterpoise sufficiently far 

 forward to avoid risk of fouhng the propeller. 



It is claimed that the rapidity with which soundings can be 

 obtained by this method renders profitable the work of sounding 

 from the ship on large scale work such as the 69 inch scale 

 common in English waters. 



The nature of the bottom must be obtained by other means, 

 such as a boat's sounding machine with " snaj)per " lead. 



