SELECTIONS

Cromwell Argus, Volume VII, Issue 326, 8 February 1876, Page 7

SELECTIONS

Eftisittg. the VangttftrcL Mention has lately been made in Home telegrams of a large air-bag which was presented to the Admiralty by the Czar of Russia to assist in raising the sunken irondad The following notice of the contrivance appears in the Times of Monday, November 15 ':■ — ' ... The Russian air-bag, or" pontoon for the raising of sunken ships, was; successfully in; natedat Portsmouth on Saturday mornnlg, not, however, by the steam air-pumps of_ the Vesuvius, as was at first attempted, but by a double-action force-pump worked by manual labor. The weight of the bag previous to inflation was 47cwt 2qr 141 b, and it was inflated to the extent of about 2£lbs to the square inch beyond the atmospheric,pressure? or jusV sufficient to display its shape and allow it to be floated to its destination. It may b 6 stated here 'that the specimen which was presented by the Emperor of Russia .to the English Admiralty, for experimental purposes, measures 22ft in length, with a dianieter of i2ft., and that it resembles a cylindrical boiler in shape, having rounded ends. The bag itself is constructed of canvas and vulcanised indiarubber, and is enclosed in strong and firmly compacted matting formed of tarred spun-yarn. The whole is enveloped jn "a netting of f-inch rope, which is further strengthened by longitudinal and transverse of strong warps. These not only enable the bag to be readily attached to the exterior sides of a sunken ship, but are so arranged as to first receive the pressure of the air from within: or rather, to feel the strain of the upward tendency of the air-bag, produced by the difference between its own weight and the weight of the water 1 which it so prevent the bag from bursting. As the bags are intended to be used at considerable depths of submergence, it is evident that any number of atmospheres maybe pumped into them without producing any distress so long as the pressure within does not greatly exceed the pressure of the water. As in the case of a balloon, however, precautions must be taken to adjust the inflation to the variations of exterior pressure as the apparatus begins to ascend, otherwise the bag would explode as the weight of the water decreased, on its approaching the surface. The necessary . adjustment is secured by Self-actingvalves, which allow the air to escape as the pressure from without is gradually withdrawn, The total displacement of the bag which was tried at Portsmouth is about sixty tons: After being inflated by means of a two-inch flexible tube, it was dragged down the incline near the King's Stairs, and launched into • the water, whence it wa3 subsequently towed by the Camel round to the Oberon hulk, which is lyittg On the Hamilton Shoal off Haslar tlospitah Oberon, it may be remembered, was long used, for experimental purposes in respect of torpedoes and submarine mines, and ultimately received the temp <fo t)Mce at the hands of the Royal Engineers, who rent open its sides amidships. It was then shoaled to prevent its sinking in deep water". It has been determined to float the Oberon into harbor to ascertain the precise damage which was sustained to the double bottom by the explosion of gun-cottdn at the last trial, and to prepare her for further experiments. As her watertight compartments fore and aft are believed to be still intact, all that is required to float her is the introduction of some buoyant power within her midship section. Air-tight barrels were, we believe, about to be tried, but as the Russian invention has arrived in the yery nick of time, the rudimentary method of securing flotation has been discarded, and the air-bag system will be subjected to a test at once crucial and practical. After being floated to the wreck, the air will be allowed to escape; the bag will then fee taken down the hatchWay, placed in the hold, inflated, and the compartments fore and aft having been cleared of water and watertight, it is expected that the" Oberon will float. But while the bag may be the means t| floating the Oberon, it is highly questionable if any number of similar bags would prove efficacious in bringing the Vanguard to the surface. The position of the vessel, no less than its immense size, is against the success of the Undertaking. The Vanguard has a displacement of 5899 tons, and besides becoming embedded in, is fast being filled with sand. On the whole, therefore, the amount of dead weight to be lifted is Upwards of 5900 tons. To lift this mass would require about eighty-five of Admiral Popoff s bags, which at £350 each, Would entail an expenditure of some £30,000 for bags alone. When to this is added the cost of labor and material, and the cost of floating and repairing the Vanguard in case of her being recovered, the total will form a tolerable proportion of the price of, a.new ironclad. But the ominous probability must not be lost sight of that, after the country has incurred the great preliminary expense, the. attempt to raise the Vanguard might not prove successful. Indeed, the successful application of the Russian sysfcern depends in a great measure upon the bags being attached to the ship by means of cables passed underneath its keel, and this is clearly impossible in the case of the Vanguard, which rests upon a level bed of sand at a depth of nearly 20 fathoms. The depth, in fact, is so great that the divers are prevented from working, not only in consequence of the extreme pressure of the water (52|lbs to the square inch), which distresses their breathing an paralyses their limbs, but by reason of the 30 fathoms or so of loose piping which draws them back. Then an-

other formidable obstacle to be encountered is the exposed situation and the very great rapidity with which the tide courses at the spot where the V'angilard lies. But the powerful set of the tide not only makes diving extremely perilous to the men employed, but, unless the bags could be almost simul : taneously attached and inflated, it would speedily destroy their buoyancy, and consequently the value of the bags, by the rubbing and chafing which they would undergo against the sides and uneven surfaces of the ship. Indeed, practical men are fast coming to the conclusion that the only thing which can be done with the Vanguard is to blow her up, and afterwards recover her guns and as much of the wreck as possible.