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

Where the railway has only a single line, as in Fig. 13, the cutting must be made narrower; the navvy is then laced out of centre, and one side road only can be used. More attention is therefore required for keeping up the supply of empty wagons ; and the jib having to swing round through a greater average distance, the output is not quite so good. In Fig. 13 is represented a cutting 25 ft. deep for a single line.

For a wide canal, Fig. 14, three or more machines slightly in advance of one another may be used, the centre one leading. A similar arrangement was employed in making the new channel of the River Witham, near Boston.