Volume Eleven - Pre-Victorian to the Present Day - some more aspects - The Steam Navvy and the Dock Extension of 1883 . . .

Dunbar & Ruston's Patent Steam Navvy.

The bucket arm is made of two oak planks, bolted together at top and bottom, so as to leave a long slot between them, through which passes the main chain. On the back edge of each plank is a rack, gearing with a pinion fixed on the fulcrum shaft on the top of the jib. The same shaft also carries a swing frame provided with four rollers, which press on iron bars or runners fixed along the front edge of the arm, so as to hold it up close to the fulcrum, while yet allowing it to be moved longitudinally by the racks and pinions for lengthening or shortening it ; the movement is given by a pitch-chain wheel on the outer end of the fulcrum shaft, driven from a pinion on the handwheel shaft, which as already explained, is under the control of the wheelman.