There is, no doubt, as Mr. Lloyd points out, a distinct advantage in small craft for such traffic, as it is obvious that a coal merchant could purchase small boat-loads of different classes of coals, to suit his customers, who could not find capital and wharf space for large cargoes of one class of coal only, and this would apply in equal degree to traffic in road-stone, bricks, drain-pipes, building materials, and many other classes of undamageable goods, and these small craft might also ply successfully on short branch canals, in districts which would not produce a sufficient traffic to warrant a large expenditure in improvement. Such locks would also, of course, accommodate craft sufficiently large to cross the estuaries of rivers, and to approach any docks with safety, and if sufficient depth of waterway is provided in the improved main lines, say 8 feet, or thereabouts, short coasting voyages might also be undertaken by craft specially constructed to do so, and also to navigate the canals.[279] Mr. Lloyd thinks that the heavy cost involved in constructing canals of sufficient size to pass craft suitable for coasting and short continental voyages would be fatal to cheap conveyance.
The largest locks hitherto constructed are those on the St. Mary’s Falls Canal, in the United States, and the Welland Canal in Canada. On the former canal the lock opened in 1851 is 515 feet in length and 80 feet wide. The great tidal lock at Eastham, on the Manchester Ship Canal, will be 600 feet long and 80 feet wide.
The Welland Canal, which is in some respects the most important in Canada, was begun by a private company in 1824 and opened in 1829. The original locks were of wood, 110 feet by 22 feet by 8 feet, and they bulged out on each side of the chamber to such an extent that they had to be hewn down from time to time to let vessels pass through. The canal was enlarged in 1841, and again in 1871, the depth of the canal having, on the occasion of the last enlargement, been increased to 14 feet. The drawing ([p. 415]) shows the general plan of the enlarged lock on this canal. It is 270 feet between the gates, 45 feet between the side walls, and has 12 to 14 feet of water upon the mitre sill.
The entire system of locks on the Manchester Ship Canal, now under construction, will be as under:—
Three locks at Eastham, namely, one 600 feet long by 80 feet wide; one 450 feet long by 50 feet wide; one 150 feet long by 30 feet wide.
Two locks at Latchford, namely, one 600 feet long by 65 feet wide; one 450 feet long by 45 feet wide.
Two locks at Irlam: similar to Latchford.
Two locks at Barton: similar to Latchford.
Two entrance locks to docks: similar to Latchford.
Small lock (Weston Marsh Lock), 229 feet long by 42 feet 8 inches wide, to connect the ship canal with the Weston canal.