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

Thus, supposing a ship to draw 16 feet and to have a length of 300 feet, the length of the slipway under water would have to be 450 feet — a most serious consideration where the provision of a rigid platform under water at every part was a sine quâ non. Again, such a slipway to be successful would require to be established in still water, and that without the use of jetties, which were highly objectionable in situations where strong currents prevailed.

He might be permitted to refer to Mr. Labat’s system at Bordeaux — alluded to in the Paper — a system of hauling up vessels broadside, and to a similar method adopted with great success at Budapest by Mr. M. Jackson, Chief Engineer of the Danube Steam Navigation Company. In some localities, and especially on the shores of silt-bearing rivers, the plan of hauling up vessels of moderate dimensions broadside on and over greased slipways, as contradistinguished from ways which had rails on them, was the best that could be adopted ; and he had no doubt that Mr. Jackson would cheerfully give the benefit of his great experience on that subject.

The cost of a modem slipway, capable of lifting a vessel of 2,500 tons, was said to be £25,000, exclusive of land. It would be highly satisfactory to know what proportion of that estimate was for foundations, the most important and the most difficult part of the structure, and also the nature of the foundations.

At Belfast, where a slipway was constructed in 1847 for vessels of 1,000 tons, the foundations had cost £12,000 out of a total expenditure of £17,000, the entire length being only 560 feet. It was a difficult matter to compare the cost of slipways with that of dry docks, sectional docks, and hydraulic lifting docks, unless the peculiarities of each case were well known and carefully considered.

Many dry docks capable of receiving vessels of much more than 2,000 tons displacement had been constructed in this country and abroad for less than £20,000 each, although instances might be given of dry docks which had cost from four to eight times that amount.