318 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



Sir J. Coode regarded the method of forming a platform, or 

 way, by merely sinking it down into a dredged bed equalized 

 by a layer of rubble stone, as an unsatisfactory engineering 

 operation, and expressed an opinion that where the rise of tide 

 is considerable, and the means exist of laying the full length in 

 the dry, a slipway may be adopted with advantage for vessels 

 of moderate size ; but where the range of tide is small, the only 

 thing that would enable an engineer to lay a slipway that would 

 warrant a ship-owner in placing a ship upon it would be to 

 construct a dam, and lay the foundation in the dry. 1 



A slipway 2 of ordinary construction, designed by Messrs. 

 Lightfoot and Thompson, is shown by Figs. 314 to 317. The 

 longitudinal timbers, or rail-bearers, are supported by transverse 

 sleepers placed close together. The cluster of timbers forming 

 the centre ways consist of three baulks of whole timbers, all with 

 scarfed and keyed joints. The outer bearers are spaced 25 feet 

 apart centre to centre, and, having but little weight to support 

 and distribute, are composed of single whole timbers. 



The rails are of cast iron. The outer ones are single, about 

 5 inches deep and 5 inches wide. The centre rails are double, 

 of nearly the same sectional area, and are connected to each 

 other by a plate on which is cast a strong rack of about 6 

 inches pitch, for receiving the holding pawls of the cradle. 

 These pawls are introduced to prevent the cradle running 

 down the way, in the event of accident happening to the 

 haul ing-gear. 



On each side of the centre rail there are wings cast on to 

 support and guide the hauling-links, which extend nearly to the 

 bottom of the ways. 



The rails must be accurately cast and laid on the timbers, 

 with an intervening layer of felt, to ensure a good bed. The 

 joints must be carefully made, and throughout the work it is 

 absolutely essential to avoid all inaccuracies, as they would 1>< 1 

 certain to lead to breakage of rollers, carriages, or rails, which, 

 although not endangering the safety of the vessel, would, never- 

 theless, seriously interfere with efficient and economical working 



The cradle 8 is a structure of timber so constructed as to 

 receive and maintain the vessel in very nearly the same trii 

 as that in which she floats. It consists of a strong centre ri 1 

 built up of several baulks of timber securely bolted together, 

 1 M.P.I.C.E., vol. Ixxii. p. 163. Ibid., p. 138. Hid., p. 139. 



