Chapter 20: Boat and Ship Raising Lifts

In modern locomotion, whether by land or water, it becomes increasingly necessary to keep the way unobstructed where traffic is confined to the narrow limits of a pair of rails, a road, or a canal channel. We widen our roads; we double and quadruple our rails. Canals are, as a rule, not alterable except at immense cost; and if, in the first instance, they were not built broad enough for the work that they are afterwards called upon to do, much of their business must pass to rival methods of transportation. Modern canals, such as the Manchester and Kiel canals, were given generous proportions to start with, as their purpose was to pass ocean-going ships, and for many years it will not be necessary to enlarge them. The Suez Canal has been widened in recent years, by means of dredgers, which easily scoop out the sandy soil through which it runs and deposit it on the banks. But the Corinth Canal, cut through solid rock, cannot be thus economically expanded, and as a result it has proved a commercial failure.

Even if a canal be of full capacity in its channel-way there are points at which its traffic is throttled. However gently the country it traverses may slope, there must occur at intervals the necessity of making a lock for transferring vessels from one level to the other. Sometimes the ascent or descent is effected by a series of steps, or flight of locks, on account of the magnitude of the fall; and in such cases the loss of time becomes a serious addition to the cost of transport.

In several instances engineers have got over the difficulty by ingenious hydraulic lifts, which in a few minutes pass a boat through a perpendicular distance of many feet. At Anderton, where the Trent and Mersey Canal meets the Weaver Navigation, barges up to 100 tons displacement are raised fifty feet. Two troughs, each weighing with their contents 240 tons, are carried by two cast-iron rams placed under their centres, the cylinders of which are connected by piping. When both troughs are full the pressure on the rams is equal, and no movement results; but if six inches of water be transferred from the one to the other, the heavier at once forces up the lighter. At Fontinettes, on the Neufosse Canal, in France, at La Louvière, in Belgium, and at Peterborough, in Canada, similar installations are found; the last handling vessels of 400 tons through a rise of 65 feet.

Fine engineering feats as these are, they do not equal the canal-lift on the Dortmund-Ems Canal, which puts Dortmund in direct water communication with the Elbe, and opens the coal and iron deposits of the Rhine and Upper Silesia to the busy manufacturing district lying between these two localities. About ten miles from its eastern extremity the main reach of the canal forks off at Heinrichenburg, from the northward branch running to Dortmund, its level being on the average some 49 feet lower than the branch. For the transference of boats an “up” and “down” line of four locks each would have been needed; and apart from the inevitable two hours’ delay for locking, this method would have entailed the loss of a great quantity of precious water.

Mr. R. Gerdau, a prominent engineer of Düsseldorf-Grafenburg, therefore suggested an hydraulic lift, which should accommodate boats of 700 tons, and pass them from the one level to the other in five minutes.

This scheme was approved, and has recently been completed. The principle of the lift is as follows:--A trough, 233 feet long, rests on five vertical supports, themselves carried by as many hollow cylindrical floats moving up and down in deep wells full of water. The buoyancy of the five floats is just equal to the combined weight of the trough and its load, so that a comparatively small force causes the latter to rise or fall, as required. By letting off water from the trough--which is, of course, furnished with doors to seal its ends--it would be made to ascend; while the addition of a few tons would cause a descent. But this would mean waste of water; and, were the trough not otherwise governed, a serious accident might happen if a float sprang a leak. Motion is therefore imparted to the trough by four huge vertical screws, resting on solid masonry piers, and turning in large collars attached to the trough near its corners. All the screws work in unison through gearing, as they are sufficiently stout to bear the whole load; even were the floats removed, no tilting or sudden fall is possible. The screws are driven by an electric motor of 150 horse-power, perched on the girders joining the tops of four steel towers which act as guides for the trough to move in, while they absorb all wind-pressure. Under normal circumstances the trough rises or sinks at a speed of four inches per second. The total mass in motion--trough, water, boat, and floats--is 3,100 tons. Our ideas of a float do not ordinarily rise above the small cork which we take with us when we go a-fishing, or at the most above the buoy which bobs up and down to mark a fair-way. These five “floats”--so called--belong to a very much larger class of creations. Each is 30 feet across inside and 46-1/2 feet high. Their wells, 138 feet deep, are lined with concrete nearly a yard thick, to ensure absolute water-tightness, inside the stout iron casings, which rise 82 feet above the bottom.

In view of the immense weight which they have to carry, the piers under the screw-spindles are extremely solid. At its base each measures 14 feet by 12 feet 4 inches, and tapers upwards for 36 feet till these dimensions have contracted to 8 feet 10 inches by 6 feet 6 inches. The spindles, 80 feet long and 11 inches in diameter, must be four of the largest screws in existence. To make it absolutely certain that they contained no flaws, a 4-inch central hole was drilled through them longitudinally--another considerable workshop feat. If shafts of such length were left unsupported when the trough was at its highest point, there would be danger of their bending and breaking; and they are, therefore, provided with four sliding collars each, connected each to its fellow by a rod. When the trough has risen a fifth of its travel the first rod lifts the first collar, which moves in the guide-pillars. This in turn raises the second; the second the third; and so on. So that by the time the trough is fully raised each spindle is kept in line by four intermediate supports.

The trough, 233 feet long by 34-1/2 feet wide, will receive a vessel 223 feet long between perpendiculars. It has a rectangular section, and is built up of stout plates laid on strong cross-girders, all carried by a single huge longitudinal girder resting on the float columns.

One of the most difficult problems inseparable from a structure of this kind is the provision of a water-tight joint between the trough and the upper and lower reaches of the canal. At each end of the trough is a sliding door faced on its outer edges with indiarubber, which the pressure of the water inside holds tightly against flanges when pressure on the outside is removed. The termination of the canal reaches have similar doors; but as it would be impossible to arrange things so accurately that the two sets of flanges should be water-tight, a wedge, shaped like a big U, and faced on both sides with rubber, is interposed. The wedge at the lower reach gate is thickest at the bottom; the upper wedge the reverse; so that the trough in both cases jams it tight as it comes to rest. The wedges can be raised or lowered in accordance with the fluctuations of the canals.

After thus briefly outlining the main constructional features of the lift, let us watch a boat pass through from the lower to the upper level. It is a steamer of 600 tons burden, quite a formidable craft to meet so far inland; while some distance away it blows a warning whistle, and the motor-man at his post moves a lever which sets the screw in motion. The trough sinks until it has reached the proper level, when the current is automatically broken, and it sinks no further. Its travel is thus controllable to within 3/16 of an inch.

An interlocking arrangement makes it impossible to open the trough or reach gates until the trough has settled or risen to the level of the water outside. On the other hand, the motor driving the lifting screws cannot be started until the gates have been closed, so that an accidental flooding of the countryside is amply provided against.

A man now turns the crank of a winch on the canal bank and unlocks the canal gate. A second twist couples the gates between the canal and the trough together and starts the lifting-motors overhead, which raise the twenty-eight ton mass twenty-three feet clear of the water-level. The boat enters; the doors are lowered and uncoupled; the reach gate is locked. The spindle-motor now starts; up “she” goes, and the process of coupling and raising gates is repeated before she is released into the upper reach. From start to finish the transfer occupies about five minutes.

If a boat is not self-propelled, electric capstans help it to enter and leave the trough. Such a vessel could not be passed through in less than twenty minutes.

Putting on one side the ship dry docks, which can raise a 15,000 ton vessel clear of the sea, the Dortmund hydraulic lift is the largest lift in the world, and the novelty of its design will, it is hoped, render the above account acceptable to the reader. Before leaving the subject another canal lift may be noticed--that on the Grand Junction Canal at Foxton, Leicestershire--which has replaced a system of ten locks, to raise barges through a height of 75 feet.

The new method is the invention of Messrs. G. and C. B. J. Thomas. In principle it consists of an inclined railway, having eight rails, four for the “up” and as many for the “down” traffic. On each set of four rails runs a tank mounted on eight wheels, which is connected with a similar tank on the other set by 7-inch steel-wire ropes passing round winding drums at the top of the incline. The tanks are thus balanced. At the foot of the incline a barge which has to ascend is floated into whichever tank may be ready to receive it, and the end gate is closed. An engine is then started, and the laden tank slides “broadside on” up the 300-foot slope. The summit being reached, the tank gates are brought into register with those of the upper reach, and as soon as they have been opened the boat floats out into the upper canal. Boats of 70 tons can be thus transferred in about twelve minutes, at a cost of but a few pence each. On a busy day 6,000 tons are handled.