Volume Two - The Era of Optimism, Investment & Development - The gridiron and slipway of the Penarth Shipbuilding & Ship Repairing Co. . . .

Broadside slipways are suitable for narrow rivers where there is no room for the length of structure which would be required for an end-on slipway. In a broadside slipway there are a number of sets of rails parallel to each other and a number of cradles. The hauling arrangement must be synchronised so that all the cradles rise or descend at the same rate. The cradles may be from 10 to 20 ft. apart, according to the weight of vessel to be supported.

Slipways require good foundations of uniform bearing power, since any inequality may cause damage to the vessel on the slip, and may also render the slipway unworkable. As the lower end of a slipway is under water a coffer-dam is necessary for its construction in most cases; on the other hand, as the weight is supported on the cradles over the under water portion of the way diminishes as the ways get deeper until, finally, the ship is afloat, such heavy foundations are not needed in this lower part as are required where the full weight of the cradles and ship is to be supported.

The inclination of the slipways varies from 1 in 15 to 1 in 30. The power required to work them depends not only on the inclination, but also on the state of lubrication, the presence of mud on the ways, and the speed of working, though the latter must necessarily be kept low.

The following formula has been given for calculating the power required:-


where W is the weight of the vessel, W1 the weight of the cradle or cradles, W2 the weight of the hauling ropes or links, all in tons; ø the angle made by the rails with the horizontal, r the radius of the rollers, r1 the radius of the roller axles, f the coefficient of friction between the axle and its bearing, and f1 the coefficient of friction between the ropes or links and the ways. (sorry for the character inaccuracies, its a software limitation!)

It was found that in a slipway having an inclination of 1 in 18, where the calculated pull required for lifting a certain vessel was 13.44 tons, the actual pull exceeded this amount by 9.44 tons, which represented the additional work required to overcome friction; and this was equal to 3.9 per cent. of the weight lifted.