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

Mr. John Thompson cont'd :

The foundation having been thus completed, guide-piles D (Fig. 2 - previous page), were driven in pairs, about 50 or 60 feet from each end of the intended platform, near the position in which it was to rest, and the platform, which was completely finished on shore, was launched like a ship and floated down between the guide-piles.

Both the guide-piles D, and the guide-timbers B, were aligned from the shore without difficulty ; but in order to obtain complete accuracy, corrected facing-pieces were affixed to the guide-piles, and corresponding facings to the platform itself, so as to bring it in absolute contact with its guides.

Chains were then attached to each side of the platform, carried over sheaves E at the tops of the piles, and being brought over to one side of the slipway, were connected together, and then attached to a winch, F, placed on a barge floating alongside. The scarp joints at the water-line junction were now carefully put into position, and watched to see that they were not displaced during the operation of sinking.

Large stones or ballast were now spread evenly over the platform, until there was sufficient weight to sink it, when it was carefully lowered by the winch. In this way any tendency of one side of the platform to sink before the other was prevented, and the platform could he placed in the position intended with certainty and accuracy.

In working under water by this system, the expense of divers’ work, preparing a foundation for a platform 360 feet long, was about £800 ; this, however, did not include the cost of slag, nor of the men employed in the barges to convey the slag.

With regard to the statement as to the strain put upon a ship by lifting it with ten or twelve presses off the cradle, he could not conceive how a ship could be much strained by such a process. There would be, no doubt, some strain, but nothing compared to what it was subject to both in launching and in meeting the waves of the ocean.

Mr. Giles had spoken of slipways of very large size ; but in the Paper, although they were referred to, they were not recommended. In several cases they had recommended their clients not to make slipways for ships of more than 320 feet long and 2,500 tons burden.