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Chwiliwch 15 miliwn o erthyglau papurau newydd Cymru

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32 erthygl ar y dudalen hon

AIR BAGS FOR RAISING SUNKEN…

Newyddion
Dyfynnu
Rhannu

AIR BAGS FOR RAISING SUNKEN VESSELS. The Titnes gives the following interesting description oi this useful discovery for raising sunken vessels :— The enormous ascensional power possessed by air when properly applied to the I urposa of raising sub- merged bodies long Biuoe pointed it out as one of the most useful agents in such operaiioi 3. The difficulty, however, was to obtain a material for making rvn p. tacles to contain the air which would offer sufficient resistance to the water-pressure at considerable depths of submergence. Ninety years since—in 1785—Pro- fessor St. C aire, of the University ot E-iinburgb, proposed the employment of ;sir Imps in raising sunken vessels, and the material which sugge- ted itself as the most desirable for the bags was india- rubber. But the india-rubber industry was then only in its infancy, and it does not appear that manufac- turers could then aid in giving practical value to the Professor's suggestions, so that the idea was not then further developed. The first appli 'ation of the air- bag system was made so recently as 1864 by M. B., tier in raising the steamer Louis, which foundered it the Lake of Boden. The operation, however, did not prove successful, the air bags bursting owing to the faulty form given to them. which was somewhat that of a balloon. In Russia the air-bag system was first introduced by M. J. Alexandrovsky, who successfully applied it in assisting to raise the turret ironclad Snurtch, whien sank in the Baltic in 1865. Admiral Popoff, of the Russian Imperial Navy, from the first realised the practical value of the invention, and mate- rially assisted M. Alexandrovsky in perfecting his system. After a course of experiments it was in time developed into a valuable means of raising sunken ships, and as such it has formed a very important ad- Sict of the Russian Imperial Naval Service, and has ewise proved useful to the mercantile marine of that country. The system as carried out in Russia consists in the employment of a series of cylindrical bags which are drawn down empty to the hull of a submerged vessel and are attached to it. Air is then pumped in from above, the bags are inflated, and the vessel is raised. This is the broad principle cf the application of the invention, which, however, is subject to various modifications, as will presently be seen. The bags are about 2U feet in length and 12 feet in diameter, and the lifting power of one of these is equal to about 60 tons. The larger baps measure 20 in length and have a diameter of 15 feet, and their lifting power is equal to about 100 tons. The cost of these bags varies from JE350 to JM75 each in St. Petersburg, according as a greater or less number is ordered. They are formed of thick canvas and india-rubber in alternate layers. The .inner and middle layers of canvas are formed of strips sewn together along the edges and placed longitudinally, or in the same way as the staves of a barrel. Between these, and on their outside, is a layer of sheet india rubber, next to which comes an outer layer of canvas formed of strips sewn together at their edges and disposed around the bag as are the hoops of a barrel, thus insuring strength and resistance against internal and external pressure. All the canvas layers are saturated with a solution of india- rubber. Over the outward canvas is a layer of matting, outside which comes a rope netting which is held up to the bags by straps, and cannot slip off when the bag is not inflated. The bags are further encased within a system of thick ropes placed around them horizontally and vertically, to which iron eyes are attached for con- necting them with the sunken vessel. By this arrange- ment the strains due to lifting are equally distributed over the entire exterior surface of the bag. In some cases a stout oaken beam is attached to the outer ropes, and the connecting chains are made fast to the beam. At the top of the air-bag and in the centre is a valve &om which proceeds the inflating hose, which is of indiarubber. In line with this hose, and at each end of the bag is a tube with a valve for the emission_of air, Which is fitted, when necessary, with a pressure gauge, by which the pressure in the interior of the bag can be ascertained. At the bottom of the bag are two lengths of hose, each opening into the bag at one end and ter- minating in a safety valve outside the bag at the other. When the bag has been fully inflated, if the air pumps be kept at'work, the surplus air will effect its escape through these valvee. The bursting of the bag is thus prevented, and an even distribution of the air pressure at the ends of the bag is secured. In the bottom of the bag, and placed directly under the inlet valve, is a manhole for the admission of a workman to inspect or Repair the bags. When not in use these bags occupy but little space, and therefore are convenient both for stowage and transport. Simple as are these useful appliances in construc- tion, in use they are no less BO. Assuming it to be required to raise a sunken veesel, divers would first descend to the wreck and ascertain the most convenient Points for passing the cables under her. That settled, Points for passing the cables under her. That settled, they would first pass a thin rope under her, with which they would draw uudcr a stouter one, by which in turn a chain cable would be hauled under. The ropes are ordinarily drawn under by means of wif: cbes on board ships above. It has, however, happened that this plan has failed to draw the cable under. In this emer- gency an air bag has been attached to the rope, and its asceusional power has been found ample to draw the cable under the vessel. The required number of chains having been drawn under the ship and made fast around her, the air bags are attached to them as near to the bottom of the ship as possible. The transverse chains are connected with a horizontal chain, which prevents them slipping laterally. Upon the baps being inflated, by means of air pumps placed on board a ship above, the submerged vessel begins to rise, and as the pressure of the surrounding water decreases, the surplus air quits the bags through the safety valves. When the sunken ve.sellieli in very deep water only a certain number of the air bags required to give floa- tation are attached to the vessel directly. Tho re- mainder, which are few in number, are made fast to chains connected with the wreck at a depth of only a few fathoms below surface. Upon inflating the bags the vessel is raised as far from the ground as the upper bagg were from the surface at starting. The ship, with all the air bags connected to it, is then floated into Shallower water, where the upper bags are detached from the chains at the surface and reattached a few fathoms lower down, when the ship is again raised to the height allowed by the upper bags and floated into still shallower water. This operation is repeated until the ship is raised to the surface, and the necessity for it arises from the fact that a vessel ascending with |reat rapidity acquires a momentum which raises it higher than is consistent with equilibrium at the sur- face, and it eventually becomes submerged again. A his is due to the continued decrease of pressure in the hags as they rise, owing to the escape of air through the valves, so that when the vessel reaches the surface the bags do not possess sufficient power of flotation to retain her in that position, and she therefore sinks ?gain. The same method of procedure is also observed ln cases where the Bhip does not begin to rise hori- 2°ntally, but with one end much higher than the Otha* vention has proved very valuable to the Rus- rernment, a number of vessels having been some of which were sunk at great depths—and irtially lifted on the surface by its aid. Among instances of its successful application was the if a merchant ship which foundered in the 1 1869, She was laden with pig iron, and, her great weight, it was resolved, if possible, ire her deck and take her cargo out after- The air bags were therefore attached with v, and when they had been inflated they to surface the deck, with the masts and together with the upper Btrakes of her rhich were torn from the hull of the thus demonstrating the power of the air- jm. In 1870 the gunboat Metch foundered in i of Tranzund in 21ft. of water, and was raised a of this system of air bags. The Ilmen was the same year in ten days, and the ironclad 'A was lifted for repairs, and was properly while-so lifted, the destruction of the lower her armour-plating, due to the action of the iheathing, being satisfactorily stopped. But lystem the vessel must have had her armour- jmoved before being docked, as at that time sre no docks which could take her in with irnr on. Similarly, in the same year, the the ironclad frigate Minin was raised, led by some barges, she was successfully I over the Neva bar to Cronstadt. In 1870, > Imperial yacht Standhart was conveyed Neva bar in thersame way, and the stern of the Prince Pojarskp was lifted by the same means. ompt was made in 1872 to raise a vessel ad mink in Biorke-Zund at a depth of 15 by means of barges, but the attempt failed. -bag system, however, was successfully ap- itwithstanding the comparatively small size, ight, and peculiar form of the vessel. In the ? year the pitch of the screw propellers of the Novgorod, required changing, and, three bags teen placed under her ptern, it was lifted 6ft. l6 water, and the necessary alterations made irew. Again, during last year the Novgorod larly twice lifted for alterations to her screws, ialtic, also, last year a mercantile vessel—the —foundered, and was raised by the air-bag notwithstanding that the ship was buried at a 11 fathoms in the mud and ooze at the bottom DM. The -air-bag system is likewise rendering istance to the engineers who are constructing bridge over the Neva at St. Peteraburgh. what has been btated it will be seen that the ystem has many advantages which admirably for the purposes for which it is required. It enoimous lifting power when the bags are in- ud when not in use they stowaway in a very >ace. In rough weather, although opera- >y have to be suspended, the work of raising is only delayed, and there is no labour away, inasmuch as the bags, uuiuflated,. can jd and left under water untilcalmer weather operations to be resumed, In the case of kat, owing to the winter setting in, the bags attached to the ship were left to themselves be winter, and operations were re-commenced jrmg at the point at which they had been re- id, no damage having been sustained in the e. It was one of these bags whiuh-as Etated Times—tbe Rusaian frigate Oiaf recently over as r. present from the R Admiralty, which experiments arc to be ma.de in order to dRptahility for raising th? V^g^ard.

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