Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/869

Rh CANAL 787 register tonnage of the vessel. The speed varied from one mile to three miles per hour, according to the size of the vessel and the state of the weather. In I860 steam-tugs were placed upon Ihe canal to do this work. They are iron boats, 65 feet long, 12 feet beam, and draw G feet 3 inches of water, fitted with high-pressure engines ; the diameters of the cylinders are 20 inches, stroke of 18 inches, pressure of the steam 32 Ib on the inch, and the cost of each 3000. Nearly the whole of the sea-going craft are now towed by these tugs. The vessels range from 30 tons up to 700 tons register, with a draught of water from G to 1 6 feet. They are towed either singly or in a team, according to circumstances. Sometimes as many as thirteen loaded vessels of from 50 to 100 tons register have been towed by one tug at the rate of 3 to 3.* miles an hour. The heaviest load drawn by any one tug has been 1690 tons of goods in three vessels. Their draught of water varied from 14 feet 6 inches to 15 feet 6 inches, and they were taken the whole length of the canal at the speed of 2 miles an hour. The smaller vessels are towed at a speed of 4 miles an hour, to which as a rule they are restricted. The employment of steam for towing has been found very advantageous. The vessels rub less against the banks, the power being right ahead, and not on one side as with horses. The wear on the ropes used in tracking is reduced, the speed is increased, and vessels can be moved along the canal in weather which would have prevented horses doing the work. With a strong wind athwart the canal vessels cannot be tracked in train ; they must then be taken singly, or at most two at a time. When vessels are towed in train, as a rule the largest and heaviest draughted are placed first, ! and the hawser leading from the first vessel to the tug is O O taken from each side of the bow. With this arrangement, and a skilful management of the tug, the vessels can be kept fairly in the line of the canal. The only disadvantage of this system, on a canal the sides of which are unprotected, is the additional wear caused by the run of water between the sides of the large vessels and the banks. Such vessels occupy a large part of the sectional area of the canal, and being taken along at a much greater speed than they were by horses the wash of water is more prejudicial. When the vessels or trains of vessels are heavy, and the tugs are working up to their full power and speed, the water thrown back by the action of the screw against the bow of the first vessel is thrown off by it to the banks on either side, and is the cause of considerable wash. This has been attempted to be remedied by placing the first vessel farther back from the tug; but in practice it is found that a distance of 40 to 50 feet is the farthest separation that can be allowed without sacrificing that hold between the two which prevents the vessel sheering from side to side. The first vessel being kept steadily in her course, the others follow without much difficulty. The employment of tugs has afforded an unexpected facility for cleansing the canal from deposit of mud. Formerly it was difficult to remove this deposit from the slopes of the banks on which it collected, sometimes in- j conveniently contracting the capacity of the canal. Since the vessels have been moved at greater speed and in trains this deposit has been entirely removed from the slopes to the bottom of the canal, whence it can readily be taken out by the dredger. But though all efforts to improve barge-canals can never bring them to compete with railways in the quick con veyance of passengers, it is surprising to find in how many places they still command an enormous traffic in goods and minerals, and thus act as a valuable relief to overburdened railwaj s. This is specially the case in the manufacturing districts of England, where the Birmingham Grand Junction and other canals seem to carry on as brisk a trade as they did in days gone by when they had no competitors but the stage coach and the carrier s van. These remarks, however, as to railway competition do Ship not apply to Ship-canals, which, undisturbed by competing canals, schemes, retain all the monopoly they ever possessed ; and indeed, in the recent construction of the Suez and New Amsterdam canals, they have acquired an importance before unclaimed for works of that class an importance which entitles them to the highest consideration in any engineering treatise ; for, apart from their structural interest to the engineer, their usefulness in affording a short and sheltered passage for sea-borne vessels has long been acknowledged and can hardly be over-estimated. The Languedoc Canal already mentioned, by a short passage of 148 miles, saves a sea voyage of upwards of 2000 miles through the Straits of Gibraltar. By the Forth and Clyde Canal sea-borne vessels, not exceeding 8-J- feet draught of water, can pass from opposite coasts of Scotland, through the heart of the country, by 35 miles of inland navigation and avoid the dangers of the Pentland Firth ; the Crinan Canal substitutes a short inland route of 9 miles for a sea voyage round the Mull of Kintyre of about 70 miles; and the last great canal between Suez and Alexandria saves vessels a tedious voyage of 3750 miles on their route to India. To most of the early ship canals that have been executed, the principles of construction already stated are generally applicable the depth of water and dimensions of the locks and all other works being increased to suit the larger size of craft which use them, and therefore further notice of such details is not required. But having still to illustrate the larger class of works, we proceed to describe some of the largest of the ship-canals already constructed and projected, and in doing so, we shall consider ship- canals under the following three classes : First, Canals which on their route from sea to sea Three traverse high districts, surmounting the elevation by locks classes of supplied by natural lakes or artificial reservoirs, such as the s lpcs Languedoc in France, or the Caledonian Canal in Scotland ; Second, Canals in low-lying districts, which are carried on a uniform water-level from end to end, and are defended against the inroad of the sea at high water by double acting locks, which also retain the canal water at low tide, such as the canals of Holland and other low countries ; Third, Canals, of which the Suez is the only example yet made, without locks at either end, and communicating freely with the sea, from which it derives its water supply. The Caledonian Canal in Scotland is as good a specimen Caledonian of works of the first class as can be selected. Canal. In 1773 James Watt was employed to survey the country between the Beauly at Inverness and Loch Eil at the mouth of the river Lochy, a distance of about 60 miles, with the view of forming a ship canal between the two seas, to save about 400 miles of coasting voyage by the North of Scotland through the stormy Pentland Firth. The district referred to, called the &quot; Great Caledonian Glen,&quot; as will be seen from Plate XXXVI., embraces a chain of fresh-water lakes, which, in connection with the surrounding glens, have afforded an interesting field for the speculations of the geologist ; and no doubt the first conception of a canal through the district owed its origin to the apparent facilities for inland navigation which the lakes afforded. 1 In 1801 Telford was employed by Government to report, and the ultimate result of that report was the construction of the canal, which was opened in 1823. The summit-level is at Laggan, between Loch Oich and Loch Lochy, whence the drainage flows to the Eastern and Western seas. Life of Telford Caledonian Canal