Ship-Lifting or Unlaunching.

“Give me a fulcrum,” said Archimedes, “and I will move the world.” We have not yet come to that point — to use matter external to the world, unless perchance meteoric iron; but we assuredly move very large things on the surface of the world, and we move them with a very unstable sort of fulcrum in its material state, but which yet by artificial means we contrive to consolidate.

“Unstable as water thou shalt not excel,” has ceased to be a perfect image for the poet. A Hebrew Caucasian, hight Bramah, doubtless as much Abraham as Braham the singer was, some score years ago caught this unstable fluid, this Undine, this water-kelpie, conjured it into an iron cylinder, with a moveable piston, fitted thereto a tiny pump which practically drove with every alternate stroke of the handle small wedges of water into the mass, gradually enlarging the bulk of the mass of water and so forcing up the piston by the accumulated power of the man’s arm, till the column of solid water below became a fulcrum capable of sustaining any number of tons’ weight that would not crush or burst the cast-iron cylinder itself, being commonly about three tons to every circular inch, equal to forty strong men. Such is the water-kelpie, held in a leash or collar of folded cow-hide by the cunning glamourie of one of our master mechanics, some sixty years since.

Three of these presses, two of them having rams or pistons eighteen inches in diameter, and one of them twenty inches, raised the Britannia tube, weighing, with its tackle, upwards of 2000 tons, one hundred feet high. But instead of a man’s arm to work the pump —heat from food acting through human muscles — the steam engine was used — heat from coal acting through water swollen in bulk, and thus rendered expansive, at every fresh pulsation driving a fresh wedge of cold water beneath the giant rams, till by gradual increment the work was done. And thus was a piece of knowledge accumulated for all time, convertible to many uses.

Archimedes, it is said, lifted ships out of the water, and swamped them — and Roman soldiers and centurions with them — by mechanical contrivance. They probably were not very large ships. But a short period has elapsed since modern engineers have taken to lifting ships out of the water, not to smash, but to examine and repair them. A large float has huge cranes in it, which take hold of cables fastened round a vessel, and she is lifted bodily by steam power, and water is pumped into the float at one part, as a counterbalance weight, while air upholds it at the other.

In the United States and elsewhere, hollow boxes of wood or iron, partly filled with water, are drawn under a vessel, and held in position. The water is then pumped out, and the pontoons by their buoyancy lift the vessel, which can then be examined and repaired.

The engineers connected with the Victoria Docks wanted to have a simple means of rapidly raising a vessel out of the water, and Edwin Clarke, one of the instinctive engineers of the day, was chosen to devise them. The ordinary construction of graving docks is an oblong space, enclosed by timber or masonry, with a flood-gate at the entrance, the sides being made to slope something to the shape of the vessel.

When the vessel enters at high tide, the gates are closed, the sluices opened, and the vessel propped in position, till the water runs out to the level of low tide, when the sluices are closed, and the remaining water, if for a very deep vessel, is pumped out. In the dock the vessel remains till all external repairs are done, when the water is let in, and the vessel floats away. In this mode the dock may be occupied many days together with one vessel.

Mr. Clarke’s object was to be able to raise a succession of vessels, and float them out of the dock as soon as raised; in this mode making one dock do the work of a dozen.

A row of cast-iron tubes, all out five feet in diameter, were sunk vertically at each side of the basin, about ten feet apart. The mode of sinking was peculiar. Being lowered to the bottom, a man in a diver’s dress was lowered inside. He dug under water, and filled pails, which were drawn up in succession, the tube gradually sinking till sufficient depth was attained; and so on in succession with all the tubes, the tops of which were connected with a framework of iron. From the top downwards, each tube was slotted parallel to the length of the dock. In this slot was a cross-head, carrying on each side a pair of long iron links. These two links were connected with two links on the opposite side of the dock, at a distance of sixty feet, by strong wrought-iron girders. At the bottom of each column was a powerful Bramah’s press, with a piston of sufficient length to carry the cross-head to the top of the tube, and with sufficient length of stroke to descend to the bottom.

Thus every pair of opposite columns laid was calculated to raise two cross beams, the columns extending the whole length of the dock. The presses were worked by a steam engine, being so connected as to form three sets of lifts, each of which sets being supplied from a common stock of water worked simultaneously, so that the middle or the ends could be raised more or less at pleasure. A kind of big gridiron was thus formed, about one hundred and sixty feet long and sixty feet wide, and capable of moving up and down through a space of some twenty feet.

Upon this gridiron was placed a huge tray or square saucer of sheet iron, rivetted together, with the edges rising upwards in vertical walls, about four to five feet high. The tray was divided into water-tight compartments by cross partitions of sheet iron, similarly to a ship, and was strutted and timbered with cross-beams to keep it in shape.

A few days back the public, ladies inclusive, were called in to behold an anti-launch, with the usual paraphernalia of spread tables and the eternal champagne bottles. The valves of the huge tray being opened, it gradually sunk under water as it filled, bearing down with it all the ram-heads with the gridiron.

A craft from Aberdeen, called the Jason, light in ballast, and feather-headed with a multitude of flags, of between eight and nine hundred tons burden, was hauled by a rope forward and pushed by a steam-tug aft, till her keel ranged fore and aft over the centre of the tray, carefully adjusted by measuring-poles, while lifting and moving.

The pumps were then set to work till the tray touched her keel, when a series of huge chocks were hauled by ropes and slid forward on the transoms of the tray till they formed a cradle all round her bottom. Then the rams were again set to work, and up went gridiron, tray and clipper ship till her keel stood some five feet above the water level, and captain and mates could walk round her as easily as a school of dolphins could swim round her in deep water. Then unmistakeably could be seen the traces in her copper of all the ricking and straining or scraping she might have undergone.

As the tray rose, the water fell through the valves, and when clear of water the valves were closed, and then the great tray floated with Jason and his Argosy, and captain and crew, and what golden fleecery they might have, all on board. The vessel was hoisted upon the tray for public inspection as deftly as Jeames of Buckley Square could hand up a letter.

Most frequenters of launches have observed how boats ply about, and their occupiers, with scoops and landing-nets, catch the floating tallow. Here also in this un-launch there was scope for the pickers-up of unconsidered trifles. Some half-dozen good-sized perch had got entangled in this giant iron sagene, and there were no weak meshes to burst through. The boys were after them, and old Father Thames must have been delighted to see them hold them up in triumph, incontestibly proving that he was not all poison, and inviting all anglers to try a punt off the Isle of Dogs, where there are positive live perch existing.

Now for a digression, to which the apropos will come. On a hot evening some ten years back I waited on the pier barge at Blackwall for a boat to cross the water. Two porters were taking the coolest place they could find, and discoursing first quietly and then excitedly. At last a screw-steamer came by, and gave point to their subject, one exclaiming, “I should like to know who inwented the first screw?”

His companion’s wit was uppermost, and he replied, “Vy Harkymeeds, to be sure.”

“Don’t believe it,” said the other; “depend on it, it was somebody behind Harkymeeds what inwented it for him, and he gave it his own name.”

In short the porter held a strong conviction that no real inventor ever got justice done to him, but that the invention was always officially appropriated; and had his fellow colloquist given the name of the direct assistant of Harkymeeds, would have been ready to testify that it had been appropriated third hand.

As usual, speech-making followed the symposium, and a director demonstrated that the new scheme was the best and most profitable and the company the most prosperous that had as yet been devised, and thereupon Edwin Clarke came to claim the very modest merit of having taken his idea from the moving of the Britannia tubes. If a tube of 2000 tons could be lifted by these hydraulic presses, 100,000 tons might be lifted by multiplying the presses; and in the details of working out he had been helped by numerous people, directly and indirectly, moreover having a body of engineers for directors, who, from time to time, corrected any crudities.

A more modest inventor never gave speech to public. He admitted the moving body behind ” Harkymeeds.” And now to the cui bono. The tray has to be lifted as well as the vessel, but there is no water to pump out as is the case with ordinary pontoons, so the cost of coal for the two processes is about equal. But then in a graving tidal dock the water runs out without pumping.

But again with the tray system, each tray may be floated away with its cargo, and one dock will serve instead of many, and a large amount of first cost and valuable space is saved; and what is more than all in time of business, the saving of time is great. Several vessels may be docked, examined, and discharged in a single tide.

It is also no slight advantage to have the vessel in daylight raised above the water’s level at will, so that a craft may be looked all over before going to sea to make sure of her trustworthiness. Nor does there appear to be any reason why the trays should not be so constructed as to be as durable as the stone dock they replace. Upon the whole, the plan is very valuable, even for a tidal water. It will be still more important where there a re no tides.

Author: W. Bridges Adams.


About libros19blog

Central Florida
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