328 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



"A small band, keyed into the first-motion shaft, was found 

 useful for hauling up the empty cradle, or for small vessels, and 

 as it ran GJ times as fast as the large barrel, it saved much time. 

 The large barrel was 5 feet in diameter and 7 feet 3 inches long, 

 and wound up a steel-wire rope 9 inches in circumference. 

 Ordinarily a single rope was used, and a light vessel of say 1500 

 tons could be hauled up without stopping ; but for heavier vessels 

 the rope was passed round a large sheave fixed to the end of the 

 cradle, giving two parts of the rope instead of one, with the 

 standing part fixed to an anchor-bolt in the foundation under 

 the steam-winch, by which the hauling power was doubled. If 

 necessary, a second pulley could be introduced, and the hauling 

 power thus multiplied threefold without putting more strain on 

 the gearing of the steam- winch. 



" The rate of haulage with the single rope was from 12 to 20 

 feet per minute, according to the weight of the ship." 



Stress in Hauling. The stress required for hauling up a 

 vessel varies very much according to the efficiency of the ways. 

 Everything being rigid, it may be found by the following 

 formula : 



S = tan 9(w + w,+ w,) + ' II f + w,f t . . (I) 1 



where S is the total pull on the links, w the weight of the 

 vessel, w l the weight of the cradle, and w 2 the weight of the 

 links, all in tons, the angle made by the rails with the 

 horizontal, r the radius of the rollers, rj the radius of the 

 roller-axle, / the coefficient of friction between the axle and 

 the bearing, and /i the friction between the links and the 

 rails. 



The total amount of pull to be provided in the hauling- 

 cylinders of Messrs. Lightfoot and Thompson's gear would be 

 this quantity S, added to the total pressure on the returning 

 ram, and what is required to overcome the friction of the 

 hydraulic apparatus. 



In practice, the values of / and f^ are difficult to determine, 

 and vary according to the state of lubrication, and as there is 

 besides another unknown element in the shape of extra pull to 

 overcome the effects produced by deflection of the ways, it is 

 usual to estimate the hauling power in a much more empirical 



1 M.P.I.C.E., vol. Ixxii. p. 145. 



