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EQUIPMENT AND INSTRUMENTS 



4633 



and watch the wire at all times. With it in this position the ship can be maneuvered 

 at will to keep the wire vertical while sounding. A fau*-lead should be carried on a 

 davit or boom to lead the wire well clear of the side. The registering sheave, or counter, 

 should be mounted near the machine where it can be conveniently read by the operator. 

 A satisfactory installation is indicated in figure 82. The wire is led through a fair- 

 lead on a boom of 2}2-inch galvanized iron pipe. The fair-lead is attached to a pipe 

 cross which turns freely on the boom, and is rigged so it can be slid along the boom 

 afid used in any position when sounding. The fair-lead is counterbalanced by an 



Figure 82. — Installation of ship sounding machine. 



adjustable weight at the top of the cross. The registering sheave msLj be seen in the 

 figure on the boom above the sounding machine. A rocker arm (not shown in the 

 figure) is usually hinged at one end to the machine or rail and has a small pulley at the 

 other end which rides on the wire. The weight of this arm continuously takes up any 

 slack and by a sudden drop indicates clearly when the lead strikes bottom. 



An accumulator spring, between the end of the boom and the stay supporting it, 

 serves the double purpose of easing the strain of sudden surges due to rolling or pitch- 

 ing of the vessel and indicating the tension when reeling in. The tie rods of this spring 

 are marked to show each 25 pounds of tension up to 150 pounds. This spring should 

 be used with piano wire for depths greater than 200 fathoms and the speed of reeling 

 in should be regulated so that the tension does not exceed 100 pounds. 



On account of the wide variation in survey launches and their power plants, no 

 one standard method of sounding-machine installation can be specified. The wire is 

 usually led through a sheave mounted on a davit overhanging the stern, although there 

 is an increasing tendency to lead the wire over the side amidships. Where the stern 

 mounting is used the registering sheave is usually on a davit which overhangs just 



