SLIPWAYS. 321 



supplementary hauling-chain, and after trimming, is ready to 

 take on another ship." 



Slipway to accommodate more than One Vessel. 1 A method by 

 which a slipway can be made available for repairing two or 

 more vessels at one time is called relieving, and is accomplished 

 in the following manner: The transverse arms of the cradle 

 connecting together the centre and side ribs, and carrying the 

 sliding bilge-blocks, instead of being permanently fixed, are 

 hinged at their outer ends to the side ribs, and are thus capable 

 of being swung round parallel with the side ribs, upon which 

 they rest when in this position. After the vessel to be relieved 

 has been hauled up, strong baulks of timber are placed between 

 each pair of transverse arms to act as bilge-blocks, capable 

 collectively of eventually carrying the whole weight of the 

 vessel. Commencing at the top simultaneously on each side, 

 these new blocks are tightly wedged against the bilge of the 

 vessel, the weight being in this manner relieved from each old 

 bilge-block, and taken by the new ones resting on the ground. 

 All the old blocks are thus relieved and slid out on the arms, 

 the vessel resting on the new blocks and on the keel-blocks, on 

 the cradle. These latter are now relieved by placing under the 

 keel at proper intervals hydraulic presses, connected with the 

 pumps. Water, under pressure, being introduced into these 

 presses, the vessel is raised just sufficient to permit the keel- 

 blocks to be knocked out, after which, on exhausting the water 

 from the presses, the ship sinks back, and is entirely carried by 

 the new blocks supported on the ground. The cradle is now 

 clear and relieved from the vessel, and so soon as the hinged 

 transverse arms are swung round into a longitudinal position, 

 can be moved down the ways, and is ready to be used for 

 another vessel. 



Another method of relieving (Thomson and Cooper's patent) 2 

 is shown by Figs. 318 to 321. Instead of employing one cradle, 

 two are used, constructed in such a manner that a vessel having 

 been hauled up to a certain point on the main cradle, can be 

 transferred to an auxiliary one, the main cradle being thereby 

 set free to receive another vessel. With this object in view, 

 the main rails of the slipway are constructed in the ordinary 

 manner, and at the ordinary inclination, but of such additional 

 length as may be required for the working of the auxiliary 

 1 M.r.I.C.R, vc4. Ixvii. p. 141. Hid., vol. Ixii. p. H2. 



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