3. EQUIPMENT AND INSTRUMENTS 



73 



Figure 21. — Hand sounding machine. 



samples, and may be used for oceanographic 

 work such as vertical lowerings of a bathy- 

 thermograph. 



3-73 Registering sheaves. — A register- 

 ing sheave (Fig. 23) consists of a grooved 

 wheel mounted in a yoke so that it will re- 

 volve freely, and connected by gears to an 

 indicator which registers the amount of wire 

 payed out. Sounding sheaves measure the 

 wire in fathoms and tenths or in meters and 

 tenths. The depths may be registered on a 

 counter or by pointers on a series of dials. 

 Each sheave must be calibrated for the size 

 of wire used in the operation. When in use, 

 the wire must be in contact with the bottom 

 of the groove in the sheave for one com- 

 plete revolution to prevent slipping. The 

 sheave may be calibrated most accurately by 

 running the wire over it for an accurately 

 measured distance along a wharf or other 

 level space. The wire must be kept taut to 

 prevent slipping during this operation. The 

 calibration should be repeated as a check. 

 Correction factors should be computed if 

 necessary (see 5-93). 



Figure 22. — LL Type electric sounding machine. 



Figure 23. — Two types of registering sheaves. 



3-74 Sounding with oceanographic 

 winch. — When the ship is equipped with 



