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

Mr. John Thompson cont'd :

As a guide for accurate execution of this work, a line of piles A, was driven on each side of the foundation, clear of the sides of the timber platform, and to these piles guide-timbers B, were affixed at the required inclination of the slipway, and at the depth of the ends of the straight-edge above it. The foundation was now ready to be dressed off true by divers, who, as they frequently had to work in the dark, were provided with iron-faced straight-edges C, made about the weight of a similar volume of water, so as to be easily moved. These were long enough to reach across the entire foundation, and to slide underneath the guide-timbers. With these straight-edges the divers were able to dress the macadam face so truly, that in one case of a foundation 360 feet long, it was found, after the platform was finished, that there was only one error of ³⁄₁₀ inch.