SLIPWAYS. 



317 



for a width of 15 feet on both sides of the slipway. The whole 

 was then planked over with 3-inch redwood deals. 



For carrying out this work, 1 a 35-feet traveller was con- 

 structed to span the slipway transversely. Longitudinal timbers 

 were laid upon the prepared ground, having ordinary rails fixed 

 upon them, the diameter of the traveller-wheels being made to 

 suit the inclination of the slipway. 



Upon this traveller was placed a steam pile-driver, with 

 40- feet ladders, and a ram weighing 21 cwt. 



The foundation was partly made ground on the foreshore, 



FIG. 3U. 



FIG. 315. 



SECTION OF WAYS 'AND CRADLE 



FIG. 316. 



FIG. 317. 



and, to obtain the requisite inclination, an average of 10 feet of 

 excavation had to be taken out at low water, and carried to the 

 upper portion of the slip, to form the necessary embankment for 

 the slipway, and also for roadways leading from the ship-yard. 



As the tide ebbed, the traveller carrying the pile-driver was 

 allowed to go down by gravitation. The piles were then driven 

 in each successive row, two and four alternately, the engine being 

 worked across the traveller from side to side of the slipway. 

 When the tide flowed, the traveller was hauled above high-water 

 level, and the piling continued at the upper portions of the slip- 

 way, until the ebb allowed operations to be again resumed at 

 the lower end. The piles varied from 25 to 50 feet in length, 

 and were driven into the clay until the set at the last blow was 

 J inch, with an 8-feet fall of the ram. 



M.P.IC.K, yol. Ixxii. p. 171. 



