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

Mr. T. B. Lightfoot cont'd :

He had read Sir Frederick Bramwell’s paper on the floating dock built for the Island of St. Thomas, and other methods of docking vessels for repairs, with much interest, and would have named it in their communication had it not been that slipways were only mentioned in it incidentally, in common with careening and other systems. The same speaker, as well as others, urged the necessity for having an absolutely rigid support or floor for the vessel in place of one of a slightly yielding nature. He regretted that no reasons had been given for that preference, for unless it could be demonstrated that the majority of vessels of the present day had perfectly straight keels, it seemed to him that a rigid support must be positively injurious.

Far from the keels being straight, they were in many instances bent considerably, sometimes to the extent of 4 or 5 inches, that bending being the result of a settlement of the wooden or iron structure, and if, when being docked, the curved, keel were compelled to settle down on a level and rigid support, it would be suddenly forced back into a straight line, an action which could not fail to set up most destructive strains. On the other hand, on a properly constructed slipway, the cradle and foundations yielded slightly, and accommodated themselves somewhat to the shape of the vessel.

It was for that reason they considered Mr. Bruce Bell was wrong when he advocated a firm and unyielding masonry or concrete foundation, and differed from those speakers who contended that a rigid support was the best. The enclosing of the tipper portion of a slip within watertight walls was of course a system only to be adopted in special cases; but it must be remembered, that not only was the amount of enclosing wall much less than that for a dry dock, but the pressures to be resisted both by the walls and by the gates, were also much less ; and therefore the cost was comparatively small. The arrangement was adopted not because slipways proper were found to be unsatisfactory for vessels of large size, but to economize length in situations where there was a tide.

Mr. Giles had instanced a dry dock constructed at a cost of 20,0001., which would accomplish all that the slipway mentioned in the paper would do. He did not know if Mr. Giles understood that the slipway would accommodate two vessels of 280 feet at one time ;