SOUNDING 277 



fathom), to the spindle of which is affixed an ordinary 

 engine-room counter. For working heavy vertical or 

 mid-water nets this sheave may be bolted to the deck, 

 but for work of a lighter character it may be slung 

 from a davit in place of the ordinary snatchblock. If 

 necessary a single turn of the wire may be taken right 

 round the sheave, but this tends to chafe stranded 

 wire. For bottom trawling the recording sheave is 

 scarcely necessary. A sufficiently good estimate of the 

 amount of warp paid out can always be made by eye 

 or by counting the revolutions of the drum, making 

 allowance for the thickness of a heavy wire, if appreci- 

 able in comparison with the sheave. 



All rollers and sheaves should be brass-bushed if 

 possible, and they should be kept drenched in oil ; 

 it is astonishing how soon oil disappears when 

 i,opo fathoms of rope are being paid out, and what 

 disaster attends a block jammed for want of it. 



2. SOUNDING. 



A sounding should always be taken before any gear 

 is shot. In surveying vessels the deep-sea sounding 

 machine is generally rigged in the bows ; it can be 

 driven by a swifter from the deck engine. Some forms 

 of deep-sea sounding machines for example, the 

 Lucas (used by the Hydrographic Office), the Sigsbee, 

 and the Le Blanc can be driven by their own little 

 engines. 



Until recently piano-wire was used for all soundings ; 

 but it is very stiff, and liable to kink and snap if not 

 checked the moment that the lead touches bottom.. 

 Instead of this, a stranded wire has come into use in 

 the Navy, of which the following is the specification : 

 Seven strands of 24 S.W.G. galvanized crucible steel 



