EFFICIENCY OF TACKLE. 



461 



Efficiency of Tackle. The efficiency of rigging as calculated from tests made by the Ameri- 

 can Bridge Company is given in Table VII. The tables may be used in calculating the loads 

 that can IK- lifted by tackle as follows: 



Given pull in lead line, to find load lifted Divide the pull by 1.20 each time line is snatched 

 or passes over sheaves other than those in tackle blocks; multiply quotient by ratio of load to 

 UM<| lim- pull, Table VII, and the result is the load lifted. For example, lead line pull of engine 

 10,000 lb.; rigging as follows: 2 snatch blocks, 2 sheaves, and 7 parts of ij in. line in main 



falls. Then Load lifted = 



10,000 



(1.20)* 

 pull in lead line, reverse above operation. 



X 4.89 = 23,600 lb. If load to be lifted is given, to find 



TABLE VIII. 

 DATA ON CHAINS. AMERICAN BRIDGE COMPANY. 



c>" 

 o? 



^ ^^J^^/f_|-V% Cham 



,1" 

 IA^ 



Total Weight oF Chain = L'(t>20) + /// 



Hook** i" Hook Chain 



-H of" ' 

 i 04 

 *----* 



Total Weight oF Chain ~L'(f-*0) +24-4 



u i it 7 4" Twin ^^ Hook Chain 

 Hook ** ^ 



*!" 



\**+-*A 



~ 1 



Tote/ Weight of Chain - L f (6-?0) +48-5 

 Usual Length of L' is 8 feet> 



Hook 



FIG. 6. CHAINS. 



