SALVAGE BY COMPRESSED AIR

Taranaki Daily News, Volume LIII, Issue 59, 18 June 1910, Page 10

SALVAGE BY COMPRESSED AIR

NEW .MEAN'S OF RAISING SUNKEN VESSELS. The attempt to raise the United States auxiliary cruiser "Yankee* is the first application to a United States warship of the British method of salvage 'by com* presed air used by Mr. John Arbuckle. The system has already proved its efficiency in the case of the raising of the steamship "Bavarian," of 1'2,000 tons, after she had run upon the rocks in the St. Lawrence river. In both the old -system and the new, the raising of a sunken vessel is accomplished by removing sufficient water from the hull of the ship to give the necessary ibuoyancy for notation. Under both methods, the space within the ship that is rid of this water is filled with air; but there is this important difference, that under the ordinary method the air is at atmospheric pressure, whereas under the Arhuokli: method it is under a pressure equal to the depth of the hold or comi partmeut from which the water is driven , out. : i «*•»< In raising ships, it has been customary ! to send down divers who, by means of patches of plating, plugs, wooden cais--1 sons, cement, etc., attempt to patch up the hole in the hull, and render the ship fairly tight. When these repairs had , been completed, .powerful pumps were installed upon the ship, or upon wrecking ; vessels moored alongside, and sufficient i waiter was ipumped out to lift the ship off the rocks and enable her to be towed to the nearest dry dock. , It frequently happened, however, that the perforations of the hull were so many or of such extent, sometimes large , portions of the bottom being torn en- • tirely away, that salvage by the pump- ■ ing method was practical!)- impossiblie. ■ This was largely due to the fact that the patchwork—plugs, canvas, cement, , and what not—was exposed to an inward , pressure corresponding to the depth of : the injured portion of the ship below water,' which pressure was so great aa to exceed the resisting strength of the temporary repairs. It occurred to Arbuckle a few years ago that there was no reason why the. compressed air method, as U9ed in driv- : ing tunnels below, rivers, should not prove effective in the salvage of sunken ships; for, if the mud, silt and waieF can .be held from entering the open end of the tunnel 'by opposing against it att air pressure equal to the water pressure at that level, it seemed probable that the water could foe expelled through the perforated bottom of a ship, ana aefa permanently at the 'level of this perforation, (by the same use of compressed air. Although it necessitates some exceeding difficult engineering work and the rxercise of considerable ingenuity, the method by which the compressed air is used : r 'freeing the ship of water is simple, anil easily understood. No attempt is made to" close the perforationa in the bottom of the hull, but great care is taken to render airtight the side* and roof of the various holds an« compartments. Air supply pipes are led into the various comparements, and compressed air is forced in and the water gradually expelled through the bottom, until the level of the water in the various holds has 'been driven down to the highest point at which the hull ha* fceea perforated. It is evident that as long a*, the air pressure is maintained, the water cannot re-enter. By estimating j thw capacity of the compartments this ' trented, and knowing the weight of the I vessel, it is possible to free the ship of 1 the exact amount of Avater to bring her Jto the surface and make her float at ' some predetermined draft. ii The "Yankee" is one of four mercjiant [ships bnilt between 1890 and 1802, which 'were pjtrchased during the war with ;! Spain and transformed into auxiliary | cruisers. Latterly she has served as a torpedo- supply ship. She is 3i)2ft long, ' 48ft 4in breadth, and draws 20ft of water on a' displacement of 6225 tons. In the salvage operations, it was decided to leave the lower holds, the engine and boiler rooms, and the greater part of the gun deck full of water, and 'lilt the ship by expelling the water from jttie' tipper portion of hold No. 1, from (the whole of the berth deck, and from 'the after portion of the gun deck. The first step was to. make special steel hatches, fasten them securely in place, and caulk them thoroughly .watertight. The gun' deck being of steel, was sufficiently watertight in itself, but the after portion l of the spar deck, being of wood and having comparatively little resisting strength', against the upward pressure of the air, it became necessary to reinforce it strongly. This was done by placing above the spar deck and upon the deck house a series of 10-inch beams, arranged in pairs, which extended the full width of the vessel.

The special steel hatches were provided with openings to which were coupled five large steel airshafts, which extended above the .surface of the water and were provided at their upper ends with air locks. The wrecking plant consists of a large schooner, which is fitted up,with living accommodation for the men; a big wrecking steamer ,upon which is installed a compressor plant capable of delivering 5000 cubic feet of free air per minute; a number of ship's 'boats, and a steam tug which makes regular trips between New Bedford and the scene of the wreck, two miles out in Buzzard's Bay. The difficulties of the work are greatly enhanced by the exposed position of the wreck, and there are necessarily many days when it is impossible to do any Work. These remarkable salvage operations have made excellent progress. The sections of the ship to i>e unwatered have been made airtight, the truss bridging over the spar deck is completed, and it is expected that very shortly, as soon ns a favorable conjunction of the wind and tides is presentcu. the "Yankee" will be brought to the surface and towed into dry dock. Considering the great depth of water in which the ship lief, her salvage will l>e one of the most remarkable feats of its kind in the history of wrecking operations.