COALING WARSHIPS AT SEA
The war between Russia and Japan has brought prominently before the public the necessity of being able to keep a war vessel well supplied with coal: a task by no means easy when coaling stations are few and far between. The voyage of Admiral Rojdestvensky from Russia to Eastern waters was marked by occasions on which he entered neutral ports to draw supplies for his furnaces, though we know that colliers sailed with the warships to replenish their exhausted bunkers. In the old days of sailing vessels, their motive power, even if fitful, was inexhaustible. But now that steam reigns supreme as the mover of the world's floating forts, the problem of "keeping the sea" has become in one way very much more complicated. The radius of a vessel's action is limited by the capacity of her coal bunkers. Her captain in war time would be perpetually perplexed by the question of fuel, since movement is essential to naval success, while any misjudged fast steaming in pursuit of the enemy might render his ship an inert mass, incapable of motion, because the coal supplies had given out; or at least might compel him to return for supplies to the nearest port at a slow speed, losing valuable time.
A TEMPERLEY-MILLER MARINE CABLEWAY COALING H.M.S. "TRAFALGAR" AT SEA
A carrier, from which are slung the sacks of coal, is hauled backwards and forwards by steel ropes stretching between the foremast of the transport and a mast rigged on the warship.
Just as a competitor in a long-distance race takes his nourishment without halting, so should a battleship be able to coal "on the wing." The task of transferring so many tons of the mineral from one ship's hold to that of another may seem easy enough to the inexperienced critic, and under favourable conditions it might not be attended by great difficulty. "Why," someone may say, "you have only to bring the collier alongside the warship, make her fast, and heave out the coals." In a perfect calm this might be feasible; but let the slightest swell arise, and then how the sides of the two craft would bump together, with dire results to the weaker party! Actual tests have shown this.
At present "broadside" coaling is considered impracticable, but the "from bow to stern" method has passed through its initial stages, and after many failures has reached a point of considerable efficiency. The difficulties in transferring coal from a collier to a warship by which she is being towed will be apparent after very little reflection. In the first place, there is the danger of the cableway and its load dipping into the water, should the distance between the two vessels be suddenly diminished, and the corresponding danger of the cable snapping should the pitching of the vessels increase the distance between the terminals of the cableway. These difficulties have made it impossible to merely shoot coals down a rope attached high up a mast of the collier and to the deck of the warship. What is evidently needed is some system which shall pay the cableway out or take it in automatically, so as to counterbalance any lengthening or shortening movement of the vessels.
The Lidgerwood Manufacturing Company of New York, under the direction of Mr. Spencer Miller, have brought out a cableway specially adapted for marine work. The two vessels concerned are attached by a stout tow-line, the collier, of course, being in the rear. To carry the load, a single endless wire rope, 3 / 8 inch in diameter and 2,000 feet long, is employed. It spans the distance between collier and ship twice, giving an inward track for full sacks, and an outward track for their return to the collier. On one vessel are two winches, the drums of which both turn in the same direction; but while one drum is rigidly attached to its axle, the other slips under a stress greater than that needed to keep the rope sufficiently taut. Since the rope passes round a pulley at the other terminal, pressure placed at any point on the rope will tend to tighten both tracks, while a slackening at any point would similarly ease them. Supposing, then, that the ships suddenly approach, there will be a certain amount of slack at once wound in; if, on the other hand, the ships draw apart, the slipping drum will pay out rope sufficient to supply the need. The constant slipping of this drum sets up great heat, which is dissipated by currents of air. As the sacks of coal arrive on the man-of-war they are automatically detached from the cable, and fall down a chute into the hold.
In the Temperley Miller Marine Cableway the load is carried on a main cable kept taut by a friction drum, and the hauling is done by an endless rope which has its own separate winches. In actual tests made at sea in rough weather sixty tons per hour have been transferred, the vessels moving at from four to eight miles an hour.
FOOTNOTES:
[19.] Cassier's Magazine.
[20.] Cassier's Magazine.
[CHAPTER XVIII]
AUTOMATIC WEIGHERS
Scarcely less important than the rapid transference of materials from one place to another is the quick and accurate weighing of the same. If a pneumatic grain elevator were used in conjunction with an ordinary set of scales such as are to be found at a corn dealer's there would be great delay, and the advantage of the elevator would largely be lost. Similarly a mechanical transporter of coal or ore should automatically register the tonnage of the mineral handled, to prevent undue waste of time.
There are in existence many types of automatic weighing machines, the general principles of which vary with the nature of the commodity to be weighed. Finely divided substances, such as grain, seeds, and sugar, are usually handled by hopper weighers. The grain, etc., is passed into a bin, from the bottom of which it flows into a large pan. When the proper unit of weight—a hundredweight or a ton—has nearly been attained, the flow is automatically throttled, so that it may be more exactly controlled, and as soon as the full amount has passed, the machine closes the hopper door and tips the pan over. The latter delivers its contents and returns to its original position, while the door above is simultaneously opened for the operation to be repeated. A counting apparatus records the number of tips, so that a glance suffices to learn how much material has passed through the weigher, which may be locked up and allowed to look after itself for hours together. The "Chronos" automatic grain scale is built in many sizes for charges of from 12 to 3,300 lbs. of grain, and tips five times a minute. Avery's grain weigher takes up to 5 1 / 2 tons at a time.
For materials of a lumpy nature, such as coal and ore, a different method is generally used. The hopper process would not be absolutely accurate, since the rate of feed cannot be exactly controlled when dust and large lumps weighing half a hundredweight or more are all jumbled together. Therefore instead of a pan which tips automatically as soon as it has received a fixed weight, we find a bin which, when a quantity roughly equal to the correct amount has been let in, sinks on to a weigher and has its contents registered by an automatic counter, which continuously adds up the total of a number of weighings and displays it on a dial. So that if there be 10 lbs. in excess of a ton at the first charge, the dial records "one ton," and keeps the 10 lbs. "up its sleeve" against the next weighing, to which the excess is added. Avery's mineral scale works, however, on much the same principle as that for grain already noticed, a special device being fitted to render the feed to the weighing pan as regular as possible. His weigher is used to feed mechanical furnace stokers. The quantity of coal used can thus be checked, while an automatic apparatus prevents the stoker bunkers from being overfilled.
Continuous weighers register the amount carried by a conveyer while in motion. The recording apparatus comes into action at fixed intervals, e.g. as soon as the conveyer has moved ten feet. The weighing mechanism is practically part of the conveyer, and takes the weight of ten feet. The steelyard is adjusted to exactly counterbalance the unloaded belt or skips of its length, but rises in proportion to the load. As soon as the conveyer has travelled ten feet the weight on the machine is immediately recorded, and the steelyard returns to zero.
Intermittent weighers record the weight of trucks or tubs passing over a railway or the cables of aerial track, the weigher forming part of the track and coming into play as soon as a load is fully on it.
Some machines not only weigh material, but also stow and pack it. We find a good instance in Timewell's sacking apparatus, which weighs corn, chaff, flour, oatmeal, rice, coffee, etc., transfers it to sacks, and sews the sack up automatically. The amount of time saved by such a machine must be very great.
Note.—The author desires to express his indebtedness to Mr. George F. Zimmer's The Mechanical Handling of Material for some of the information contained in the above chapter; and to the publishers, Messrs. A. Crosby Lockwood and Son, for permission to make use of the same.
[CHAPTER XIX]
TRANSPORTER BRIDGES
When the writer was in Rouen, in 1898, two lofty iron towers were being constructed by the Seine: the one on the Quai du Havre, the other on the Quai Capelier, which borders the river on the side of the suburb St. Sever.
The towers rose so far towards the sky that one had to throw one's head very far back to watch the workmen perched on the summit of the framework. What were the towers for? They seemed much too slender for the piers of an ordinary suspension bridge fit to carry heavy traffic. An inquiry produced the information that they were the first instalment of a "transbordeur," or transporter bridge. What is a bridge of this kind?
Well, it may best be described as a very lofty suspension bridge, the girder of which is far above the water to allow the passage of masted ships. The suspended girder serves only as the run-way for a truck from which a travelling car hangs by stout steel ropes, the bottom of the car being but a few feet above the water. The truck is carried across from tower to tower, either by electric motors or by cables operated by steam-power.
The transporter bridge in a primitive form has existed for some centuries, but its present design is of very modern growth. With the increase of population has come an increased need for uninterrupted communication. Where rivers intervene they must be bridged, and we see a steady growth in the number of bridges in London, Paris, New York, and other large towns.
Unfortunately a bridge, while joining land to land, separates water from water, and the dislocation of river traffic might not be compensated by the conveniences given to land traffic. The Forth, Brooklyn, Saltash, and other bridges have, therefore, been built of such a height as to leave sufficient head-room under the girders for the masts of the tallest ships.
But what money they have cost! And even the Tower Bridge, with its hinged bascules, or leaves, and bridges with centres revolving horizontally, devour large sums.
Wanted, therefore, an efficient means of transport across a river which, though not costly to install, shall offer a good service and not impede river traffic.
Thirty years ago Mr. Charles Smith, a Hartlepool engineer, designed a bridge of the transporter type for crossing the Tees at Middlesbrough. The bridge was not built, because people feared that the towers would not stand the buffets of the north-easterly gales.
The idea promulgated by an Englishman was taken up by foreign engineers, who have erected bridges in Spain, Tunis, and France. So successful has this type of ferry-bridge proved, that it is now receiving recognition in the land of its birth, and at the present time transporter bridges are nearing completion in Wales and on the Mersey.
THE LATEST TYPE OF BRIDGE
The Transporter Bridge at Bizerta, Tunis. It has a span of 500 feet, and the suspension girder is 120 feet above high water, so that the largest vessels may pass under it from the Mediterranean to the inland lakes. The car is seen near the bottom of the right-hand tower.
The first "transbordeur" built was that spanning the Nervion, a river flowing into the Bay of Biscay near Bilbao, a Spanish town famous for the great deposits of iron ore close by. A pair of towers rises on each bank to a height of 240 feet, and carry a suspended trussed girder 530 feet long at a level of 150 feet above high-water mark. The car, giving accommodation for 200 passengers (it does not handle vehicles), hangs on the end of cables 130 feet long, and is propelled by a steam-engine situated in one of the towers. Motion is controlled by the car-conductor, who is connected electrically with the engine-room. The lofty towers are supported on the landward side by stout steel ropes firmly anchored in the ground. These ropes are carried over the girder in the familiar curve of the suspension bridge, and attached to it at regular intervals by vertical steel braces. The cost of the bridge—£32,000—compares favourably with that of any alternative non-traffic-blocking scheme, and the graceful, airy lines of the erection are by no means a blot on the landscape.
The second "transbordeur" is that of Rouen, already referred to. Its span is rather less—467 feet—but the suspension girder lies higher by 14 feet. The car is 42 feet long by 36 broad, and weighs, with a full load, 60 tons. A passage, which occupies 55 seconds, costs one penny first class, one halfpenny second class; while a vehicle and horses pay 2 1 / 2 d. to 4d., according to weight. The car is propelled by electricity, under the control of a man in the conning-tower perched on the roof.
At Bizerta we find the third flying-ferry, which connects that town with Tunis, over a narrow channel between the Mediterranean Sea and two inland lakes. It replaced a steam-ferry which had done duty for about ten years.
The lakes being an anchorage for war vessels, it was imperative that any bridge over the straits should not interrupt free ingress and egress. This bridge has a span of 500 feet, and like that at Bilbao is worked by steam. Light as the structure appears, it has withstood a cyclone which did great damage in the neighbourhood. It is reported that the French Government has decided to remove the bridge to some other port, because its prominence would make it serve as a range-finder for an enemy's cannon in time of war. Its place would be taken either by a floating-bridge or by a submarine tunnel.
The Nantes "transporter" over the Loire differs from its fellows in one respect, viz. that it is built on the cantilever or balance principle. Instead of a single girder spanning the space between the towers, it has three girders, the two end ones being balanced on the towers and anchored at their landward extremities by vertical cables. The gap between them is bridged by a third girder of bow shape, which is stiff enough in itself to need no central support. The motive power is electricity.
All these structures will soon be eclipsed by two English bridges: the one over the Usk at Newport, Monmouthshire; the other over the Mersey and Manchester Ship Canal at Runcorn "Gap," where the river narrows to 1,200 feet.
The first of these has towers 250 feet high and 685 feet apart. The girders will give 170 feet head-room above high-water mark. Five hundred passengers will be able to travel at one time on the car, besides a number of road vehicles, and as the passage is calculated to take only one minute, the average velocity will exceed eight miles an hour. The cost has been set down at £65,000, or about one-thirtieth that of a suspension bridge, and one-third that of a bascule bridge. The bridge is being built by the French engineers responsible for the Rouen transbordeur.
Coming to the much more imposing Runcorn bridge we find even these figures exceeded. This span is 1,000 feet in length. The designer, Mr. John J. Webster, has already made a name with the Great Wheel which, at Earl's Court, London, has given many thousands of pleasure-seekers an aerial trip above the roofs of the metropolis. The following account by Mr. W. G. Archer in the Magazine of Commerce describes this mammoth of its kind in some detail:—
"The two main towers carrying the cables and the stiffening girders are built, one on the south side of the Ship Canal, and the other on the foreshore on the north bank of the river; and the approaches consist of new roadways, nearly flat, built between stone and concrete retaining walls as far as the water's edge, and a corrugated steel flooring, upon which are laid the timber blocks on concrete, resting on steel elliptical girders and cast-iron columns. The roadway in front of the towers is widened out to 70 feet, for marshalling the traffic, and for providing space for waiting-rooms, etc. The towers are constructed wholly of steel, rise 190 feet above high-water level, and are bolted firmly to the cast-iron cylinders below. Each tower consists of four legs, spaced 30 feet apart at the base, and each pair of towers are 70 feet apart, and are braced together with strong horizontal and diagonal frames. Each of the two main cables consists of 19 steel ropes bound together, each rope being built up of 127 wires 0·16 inches in diameter. The ends of the cable backstays are anchored into the solid rock on each side of the river, about 30 feet from the rock surface. The weight of the main cables is about 243 tons, and from them are suspended two longitudinal stiffening girders, 18 feet deep, and placed 35 feet apart horizontally, the underside of the girders being 82 feet above the level of high water.... Upon the lower flange of the stiffening girders are fixed the rails upon which runs the traveller, from which is suspended the car. The traveller is 77 feet long, and is carried by sixteen wheels on each rail. It is propelled by two electric motors of about 35 horse-power each.... The car will be capable of holding at one time four large wagons and 300 passengers, the latter being protected from the weather by a glazed shelter.... The time occupied by the car in crossing will be 2 1 / 4 minutes, so, allowing for the time spent in loading and unloading, it will be capable of making nine or ten trips per hour. This bridge, when completed, will have the largest span of any bridge in the United Kingdom designed for carrying road traffic, the clear space over the Mersey and Ship Canal being 1,000 feet.... The total cost of the structure, including Parliamentary expenses, will be about £150,000."
Mr. Archer adds that, in spite of prophecies of disastrous collisions between transporter cars and passing ships, there has up to date been no accident of any kind. To those in search of a new sensation the experience of skimming swiftly a few feet above the water may be recommended.
[CHAPTER XX]
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.
By permission of] [Mr. Gordon Thomas.
A BOAT LIFT
A canal barge lift which has superseded ten locks at Foxton, Leicestershire. Two tanks, balancing one another, run on separate tracks up and down an incline. At the bottom and top of the incline the tank is submerged so that a barge may float in or out.