34 



U. S. COAST AND GEODETIC SURVEY 



89. Installation of pulleys. — The standard pulley now used for 

 the counterpoise wire and tension weight cord are 4 inches in diam- 

 eter and weigh 1 pound each. For the arrangement illustrated in 

 figure 17, six such pulleys are required, two being used as movable 

 pulleys attached to the weights and the other four as fixed pulleys 

 which are secured to the ceiling of the tide house by screw eyes. 

 Under operating conditions the fixed pulleys do not hang vertically 

 but are deflected by an amount depending upon the weight of the 

 pulley itself and the strain on the wire or cord. In order that the 

 wire may pass vertically upward from the gage and also to provide 

 for parallelism in the strands supporting the movable pulley and 

 weight, it is necessary to make allowances for the deflection of 

 the fixed pulleys when securing them in position. Computations 

 depending upon the counterpoise weights used with different float 

 drums have been made and the results are given in the table below. 

 In these computations the distance from the center of the pulley sheave 

 to the end of the supporting hook is taken as 4 inches and a small 

 allowance has been made for the depth of the groove in the sheave. 



Float drum 



6-inch 



9-inch 



12-inch 



16-inch 



24-inch 



Counterpoise weight 



Counterpoise with pulley. 

 Counterpoise wire tension 



Float wire tension 



Offset, puUey-A 



Offset, pulley-B 



lib 



21b _ 



lib 



lib 



+Hinch-.. 

 4 inches 



21b 



31b 



11^ lb 



lib 



— Jriinch.. 

 39i inches. 



31b 



41b 



21b 



lib.. 



— H inch... 

 3H inches .. 



41b 



51b 



2Hlb.--. 



15 oz 



—H inch. 

 3?i inches 



61b. 

 71b. 

 31.2 lb. 

 14 oz. 

 — H inch. 

 3H inches 



The offset of pulley -A for the counterpoise wire indicates the position 

 of the screw eye for the support of the fixed pulley immediately above 

 the gage as measured from a point in the ceiling in a vertical tangent 

 to the counterpoise drum on the side from which the wire is led. The 

 measurement is to be made in the direction toward which the wire 

 leads if preceded by the plus sign and in the reverse direction if 

 preceded by a minus sign. The offset of pulley-B indicates the 

 position of the screw eye for the second pulley as measured from thf. 

 point of attachment of the fixed end of the wire, the latter being 

 in line with the two fixed pulleys. Measurements for the installation 

 of the pulleys for the tension weight cord are made in a similar manner, 

 the offsets being those corresponding to the 6-inch float drum, provided 

 that a 1-pound tension weight is used. In this case the first offset 

 is measured from a point vertically above the tension weight drum. 

 90. In order that the gage may be operated to its full capacity in 

 recording extreme ranges of tide, it should be the aim to have the 

 adjustment such that at approximate mid-extreme tide level the float 

 drum and counterpoise drum will each be half filled with wire, the 

 counterpoise half way between the limits of its motion, and the re- 

 cording pencil near the middle of the main roller. As the larger of 

 the counterpoise drums contains 14 feet of wire when filled, a fall 

 of 7 feet for the counterpoise weight as supported by a movable pulley 

 will be sufficient for the maximum limits of the gage operation. These 

 limits would require a ceiling height of approximately 8 feet including 

 an allowance of 1 foot for the combined length of the counterpoise 



