464 HYDROGRAPHIC MANUAL PaGE 392 



enough to ensure that the wire will clear the stern and not Hkely be fouled by the 

 propeller. Where the wire is led amidships, the arrangement is similar to that used on 

 survey ships. A boom is rigged of different sizes of pipe, which will telescope into one 

 another and be out of the way when not in use. The registering sheave is inboard with 

 a fair-lead on the outer end of the boom. The advantages of the midship installation 

 are that one of the anglemen can supervise operations more closely and can verify the 

 sheave reading more conveniently, and it is more conveniently located for reading a 

 thermometer for the temperatures required in a launch echo-sounding survey. 



A hand sounding machine may be located in any convenient space, usually on the 

 stern, where there is room for the men needed to operate it. The location of a power- 

 driven machine depends more on the type and location of the power plant of the launch. 

 It is usually more satisfactory to derive the power from the forward end of a gasoline 

 engine, as this interferes less with its operation. For this reason the sounding machine 

 is usually installed inside the hull near the forward end of the engine, if there is avail- 

 able space for it. It is then connected to the engine either by a belt or chain drive to 

 the flywheel, or by a system of gears and shafting to the jackshaft. Where installed 

 on the stern deck the connection is to the clutch shaft. A V-type of leather belt drive 

 is preferred to any other type of drive because it is much more silent in operation. 



Any power machine should be bolted through the deck beams or secured to a base 

 plate which itself is bolted through the deck beams. Where the sounding machine is 

 installed forward of the engine and sounding from the stern is preferred, the wire 

 may be led overhead tlii-ough two fau--leads suspended from the canopy and through 

 a window cut in the canopy to a registering sheave astern. 



464. Registering Sheaves 



A registering sheave is a device used to measure the amount of wire payed out 

 when sounding. It consists of a grooved wheel (circumference 23.911 inches) mounted 



Figure 83. — Registering sheave. 



in a yoke so that it will revolve freely, and connected by gears to an indicator on which 

 the number of fathoms of wire run over the wheel is indicated. The preferred type 

 of indicator is a counter, the numerals of which indicate fathoms and tenths of fathoms, 



