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

Mr. Bruce Bell cont'd :

In the description of the mode of relieving the cradle from the ship in order to take up another vessel astern, the Authors observed that this was " an improvement which had been introduced of late years, " and they went on to state that the traverse arms, " 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, " and they then described the process of relieving the cradle. He could not say whether Mr. Thomas Morton originally fixed the arms in a permanent manner, but he could say that he had never seen one of Morton's cradles with arms so fixed ; and he knew that in the cradle furnished by Messrs. S. & H. Morton for the slip-dock constructed by him at Stornoway, thirty-six years ago, the arms were not so fixed, and that he relieved the cradle in precisely the same manner as described by the Authors (with the exception of swiveling the arms to take up another ship. In fact, all Morton's cradles, long before this time, were relieved in this manner.

As regarded the swiveling of the arms, and the introduction of hydraulic presses to relieve the keel, both systems had been in use on the Clyde for upwards of thirty years. The first set of these swivels were fitted upon the cradle of the Kelvinhaugh slip thirty-three years ago ; the cradle was also fitted with a set of Scott's keel-blocks, which could all be started at one lift, one connecting-pipe passing through the the whole set ; thus a ship was eased up bodily by a single pump. In view of this he could hardly see how the mode of relieving the cradle as described could be claimed as " an improvement introduced of late years. "

The great length of slipway extending under water, and consequently valueless, was one of the chief drawbacks of a slip-dock. The first design for a dock on this system was made for the Nelson slip-graving dock at Rotherhithe on the Thames in 1854, and was constructed in the following year. Another novel feature in this dock was the form of the ways, which in place of being laid on a straight incline were laid upon a curved incline, the bottom of the cradle being shaped to the same curve, the ways concave and the bottom of the cradle convex.