Volume Ten - Pre-Victorian to the present day - even more aspects - The Patent for the Penarth Slipway - 1881 . . .

Having now generally described the construction and working of a slipway, it is intended to consider some improvements lately introduced in the cradles, and to enter more fully into the various systems of hauling gear.

A method by which a single slipway can be made available for repairing two or more vessels at one time is of obvious importance, the single set of expensive hauling-up machinery, and the single cradle doing double or treble work, and so reducing the amount of capital invested, in proportion to the value of the repairs effected. This improvement, which has been introduced of late years, is called relieving, and is accomplished in the following manner : -

The transverse arms of the cradle connecting together the centre and side rails, 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 balks 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, and 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 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. In this manner lengthening can be readily carried out by cutting the vessel before taking it off the cradle, and relieving each part separately, the second part being moved down the way upon the cradle for a distance corresponding with the additional length required. As a matter of arrangement, it is, of course, necessary to place those vessels requiring the longest time for repairs at the upper part of the ways.