THE STEAMSHIP AUSTRAL.

Daily Telegraph (Napier), Issue 3637, 9 March 1883, Page 4

THE STEAMSHIP AUSTRAL.

The following is an outline of the means employed by Mr Eldridge, the Orient Company's naval architect, in raising the Austral, aud Avhieh, as our readers are aware have proved so successful. Tho Sydney Morning Herald says :—" The best authorities in England having been consulted by the directors of the Company as to the best'means of raising the Austral, the plan resolved upon Avas the construction of a ' coffer-dam.' Its main principle is merely that of a dam for keeping back water". In harbor works, forinstance, Avhere it is necessary to shut off the Avater from the bank or shore, it is customary to drive two rows of piles with a space between the rows, Avhieh is filled up with clay. By that means a kind of false bank is made, which keeps the water back while operations are carried on between the dam and the shore. In the case of tho Austral it would be absolute necessary before attempting to raise her to pump 'the water out: but the very first to be done was to make provision for keeping the water out when it avus pumped out. "The simplest and most effective method was to construct a dam all round the upper part of the ship. In other words, the sides of the vessel Avill be built up above the Avater, so that instead of being entirely submerged, its at present, she will be a fewfeet above the surface. The water Avith Avhieh she is noAv filled will then be pumped out, and the vessel should then rise by her own buoyancy. The steamship lies in about 52 feet of water at the deepest part. No part of the deck reaches the surface. The forepart is only lSin under Avater at low tide, but in the aftcrpart there is, m one corner, 2G-J-ft of water washing over the upoer deck. The coffer-dam commences at the upper deck, and Avill, Avhen finished, reach above the surface, the full length of the vessel. It is being made of planks of kauri pine, strongly fitted together, and forming a Avail lOin in thickness. It is made m sections 16ft in length. Each section Avhen completed, is loAvered and strongly secured in its place by divers. Already the forepart of tho ship has been treated in this way, but the heaviest work has yet to be performed in the aftcrpart, where there is from 20ft to 20ft head of water to contend Avith. The fixing of this coffer-dam nr wall is, however, by no means the most difficult part of the work. A\ lule the ship is full of water the outer pressure against this wail is at present neutralised by the resistance of the water on the inner side, but when the pumps are put in operation this resistance will, of course be removed, and the Avail Avillhave to Avithstand the enormous lateral pressure of 01b to the square inch. In order, therefore, to prevent a collapse, tho two Avails Avhieh will extend along the ship from stem to stern will have to bo shored up on the inner sides. In the fore part of the ship this has already been done. Not only are there great strongbeams extending horizontally from side to aide, but there are numerous powerful supports extending across the A-essel diagonally. The same thing will be done the full length of the ship, the wall or cofferdam being also shored against the masts Avhcrevcr practicable, so that it will be, for all practical purposes, as strong as the permanent sides of a ship. AVheu'"this walling is completed all round it will, instead of being caulked, which would be a Avork involving' great delay, be made watertight by means of an outer covering of canvas. For this purpose 26,000 square feet of canvas will be required. As already stated, there arc about 100 men engaged at the ship. Of these 16 are divers, one of whom was sent from England and another is expected to arrive within a few days. Mr Eldridge speaks very highly of the manner in which some of the local divers do their work. Pumping machinery has been obtained from Melbourne. The machinery Avill be capable of puming 230 tons per minute. The operations arc rendered somewhat more difficult than is usually tho case v/ith sunken A-essels, iv consequence of the slight rise and fall of the tide in Syduoy Harbor. The maximum rise and fall is about five feet. This affords very little opportunity for taking advantage of a low tide. In some port's, where there is a rise and fall of say 30 feet a great deal of work can be done at low tide. At Milford, for instance, where there is a fall of about 30 feet, they have what is technically known as a ; gridiron,' upon which vessels rest when left high and dry by the receding 'tide. Even such a largo vessel as the Great Eastern has by those means had her under sides cleaned and painted at low tide Avithout the delay and expense of docking. In connection with the Austral, however, the rise and fall of the tides has been so slight as to be of very little advantage. AVhen all the necessary preparations have been completed pumping will commence, and it is anticipated that when a quantity of water equal to the weight of the slip has been pumped out of her she will become sufficiently buoyant to move. She Avill then be gradually "drawn in shore into shallower water, and grounded until she can be fairly set afloat. The coffer-dam will then, of course, have to be stripped off, and the vessel docked. She is at present resting on a sandy bottom, and the direction iv which she is to be dragged is, it has been ascertained, perfectly free from rocks."