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

Mr. T. Summers cont'd :

The third slipway where wire rope was used for haulage was their own smaller one. This had been worked for many years with ordinary chain, and, as that was found to be a slow process in consequence of the frequent “ fleets,” and as the links of the chain when passing over the barrel always bent, and frequently broke, they determined to alter the steam winch to suit wire rope. That had been successfully done, and much heavier vessels than before were now handled by the introduction of a large sheave fixed to the end of the cradle, giving two parts of rope instead of one, with the standing part fastened to an anchor-bolt in the foundation under the steam winch.

The rate of haulage with the single part of rope was from 12 to 20 feet per minute, according to the weight of the ship, and vessels had been frequently hauled up in forty minutes after they were blocked. The saving in time and expense of this system, as compared with the hydraulic method, was considerable, and on the first cost probably one-half or one-third. By the introduction of the sheave at the end of the cradle, and so hauling by two parts of the wire rope instead of one, the hauling power was doubled, and, if necessary, a second pulley could be introduced, and the hauling power thus multiplied three-fold, without putting any more strain on the wire rope or the gearing of the steam winch.

For instance, it was contemplated to fit the system to a slip suitable for vessels weighing 3,000 tons, to which must be added the cradle weighing 250 tons, or a total of 3,250 tons. Adding one-half for the friction of the cradle, would give a gross of 4,875 tons, on an inclination of 1 in 24, producing a strain on the wire ropes of 203 tons. Messrs. Bullivant guaranteed a strength of 360 tons with a rope 12 inches in circumference, so that two parts of such rope would have 720 tons of ultimate strength. Then 720 tons, divided by the strain of 203 tons, would give a factor of safety of three and a half. As before remarked, that could be increased by adding another sheave, so that vessels weighing 4,000 tons could be easily hauled up. If a small or light vessel had to be hauled up one part only of rope would be used, and the ship would come up rapidly.