In Sweden, as well as in Holland, where the channels are narrow, the usual speed is 3½ miles per hour, but 5 miles an hour is frequently attained, the difference depending on the area of cross-section.
In curves and shallows, in narrow canals or rivers, a breaking wave first appears at from 3 to 3½ miles per hour. At 4 miles an hour the effect of the wave on the banks becomes injurious. At 5 miles an hour the wave increases, breaking over the towing-path, and being followed by other waves in succession. In parts of the Clyde, from 120 to 150 feet wide, and about 10 feet deep, vessels of from 120 to 150 feet long, with from 16 to 18 feet beam, and from 5 to 6 feet draught, are propelled by engines of from 80 to 100 horse-power, at a speed of from 8 to 9 miles per hour. At this speed a surge rises at from 2 to 3 miles ahead, and a wave is caused, which measures 8 or 9 feet from the crest to the bottom of the trough.[289]
A speed of 5 knots per hour, or 8·37 feet per second, corresponding to a head of 1·08 foot of water, is the limit of speed fixed for the Suez Canal. This may perhaps be taken as the normal speed to be sought on the canals of England. On the determination of the normal speed, and of the tonnage of the boats to be accommodated, will depend, not only the steam-power required, but the section of the canals and the dimension of the locks. A speed of 30 miles a day, including stoppages, is even now attainable on English canals.
The rate of speed on a canal is, of course, affected by the size as well as by the number of the locks, by the depth of the waterway, and by the tonnage of the craft that navigates it. On some English canals there is a lock to be passed through about every half mile, and the rate of speed is under a mile per hour.[290] On others, however, a speed of 3 miles may be kept up pretty well. The economical rate of speed is often put at 2½ miles. At a higher rate of speed the cost of maintenance of the canal would be likely to counterbalance the saving due to quicker transit. Speed is also affected by differences of gauge, which in some cases compels cargo to be transhipped with much loss of time that might be obviated with a uniform gauge.
The size of craft which can traverse a through route depends on the least navigable depth in the canal and over the sills of the locks, and the least width and length of any lock along the route. Unfortunately, very few through canal routes exist in England which are not obstructed by some narrow locks, or shallow portions of canal, rendering the comparatively good width and depth of the remainder quite unavailable for a larger craft. In France, the same want of uniformity of gauge on the waterways has hitherto existed; but as almost all the waterways are under the control of the State, improvements and extensions have been constantly in hand; and we have already seen that in 1879 a law was passed for providing a uniform depth of 6½ feet, locks 126⅔ feet long and 17 feet wide, and a clear height of 12 feet under the bridges, throughout the principal lines of waterway in France. The works for securing this uniformity are being gradually carried out; and when they have been completed, 300-ton barges, 126⅓ feet long, 16½ feet wide, and 6 feet draught, will be able to traverse all the principal waterways of the country.
The depth of English canals ranges, for the most part, from 3 feet to 5 feet; but the Severn navigation to Gloucester affords a depth of 6 feet; the Gloucester and Berkeley Canal, 15 feet; the Aire and Calder navigation, 9 feet; and the Forth and Clyde Canal, 10 feet. The locks range in size from 72 feet length, 7 feet width, and 3½ feet depth of water over the sills, up to 215 feet by 22 feet by 9 feet on the Aire and Calder navigation.
It goes without saying that if the average rate of speed that can be maintained on a canal does not exceed 3 or 4 miles per hour, the canal will never compete with the railway as a quick means of transport. The use of such waterways would thereby be limited to heavy traffic, in the delivery of which time was a matter of minor importance. But more than two-thirds of all the traffic carried on British railways, and indeed on railways generally, is of this character. The question thereupon arises, Is the economy of water transport sufficient to compensate for a slower rate of speed? Sir James Allport, who, of course, held a brief for the railway interest, informed the Canal Committee of 1883 that the railway engine would accomplish ten times as much work as a canal boat, and would do in an hour what would occupy a day on a canal.[291] Mr. F. Morton, on the other hand, speaking as a railway and canal carrier of experience, declared that, in conveying minerals between North and South Staffordshire, railway waggons and canal boats averaged about the same time—seven to eight days.[292] However this may be, there can be no doubt that where canal transport is efficient it is much cheaper, and that is the main thing for the trader.
Mr. Bartholomew has made an elaborate series of inquiries and experiments upon the Aire and Calder Canal, with a view to determine the cost of different systems of canal haulage, and has found the results to be as under:—
- With steam tugs, carrying cargoes, 1⁄34d. per ton per mile.
- ” ” ” not carrying cargoes, 1⁄7d. ” ”
- ” horse haulage,⅕d. ” ”
The lowest of these charges is not comparable with the lowest railway rate of which we have ever heard, while the highest is much below what railway managers usually state to be the cost of carrying their cheapest traffic.