During the present naval warfare we have had the opportunity to watch the sinking of ships of every type and size; shortly after receiving their death wound the vessels usually disappear totally beneath the surface. It takes even big steamers only between four and ten minutes to sink, after being hit by a torpedo or shell beneath the water line, and yet occasionally a ship may float several hours before going down to the bottom of the sea.
It is clearly evident that the slow or rapid sinking of a ship depends on the distribution of its bulkheads andwater-tight compartments. A man-of-war, built on the latest models, has a great many small water-tight compartments, for she is meant to be able to continue fighting even after several of these compartments have been destroyed; whereas, an ocean steamer is so constructed that she will remain afloat only a short time after a collision with another ship, or if she runs into an iceberg or a derelict, she can endure a certain intake of water, and lists at a moderate angle far more readily than a warship, whose guns are rendered nearly useless if the ship is heavily canting. A warship must be built so as to withstand, without sinking, the injury caused by a number of gun holes even beneath the water line, where the inner part of the ship must necessarily be subdivided into manyparts. A warship is built at great cost, but so is an ocean steamer. The sunken "Lusitania" was worth 35,000,000 marks (nearly $9,000,000) and the mammoth steamers of the Hamburg-American Line, the "Imperator," the "Vaterland," were still more expensive to build.
The ordinary commercial steamer often has in her inner construction only athwartship bulkheads through the double bottom that run from one side to another and form large partitions; and in proportion to her height a steamer is again subdivided horizontally into several decks. But these are not usually water-tight, and the cross bulkheads already mentioned form the only water-tight divisions in the hold. In the big cargo spaces, these divisions practically do not exist, and the ship,throughout almost its whole interior, is open from keel to deck. This arrangement, of course, facilitates the rapid loading and unloading of the cargo; therefore, in this type of ship the engine rooms and boilers, surrounded and protected by coal bunkers, are the only really water-tight portions of the ship. Whoever has gazed down into the capacious hold of such a steamer will readily understand that if the water should pour into one of these spaces, at either end of the ship, the other end of the vessel would rise steadily upwards. In nearly every case, even the largest steamer, just before sinking, tilts abruptly its bow or stern straight up out of the sea, until the water rushing into the hold draws the vessel downwards, and with a mighty roar it plunges forever into the deep. Wehave repeatedly noticed at this moment that the air within the boat escapes with a shrill whistle from every possible aperture, and the sound resembles the shriek of a steam siren. This is a wonderful spectacle to behold!
The velocity with which a ship sinks depends on the size of the hold, and its distance from the ship's center of gravity, for the suction occurs more rapidly if the ship is struck at either end than if the blow is delivered amidships.
We are seldom concerned with ships having empty holds; those we pursue usually carry heavy cargoes, and therefore the water can only penetrate within, where space and air exist; whatever air is left around loosely packed bales and boxes must be driven out before the water can stream in;certain exceptional cargoes, like wool and cereals, absorb a given amount of water, but these can be discounted.
British Hospital Ship Gloucester CastleCopyright by Underwood & Underwood, N.Y.BRITISH HOSPITAL SHIP GLOUCESTER CASTLE, SHOWING RED CROSS ON BOW,SUNK IN THE ENGLISH CHANNEL BY A GERMAN SUBMARINEToList
Copyright by Underwood & Underwood, N.Y.
BRITISH HOSPITAL SHIP GLOUCESTER CASTLE, SHOWING RED CROSS ON BOW,SUNK IN THE ENGLISH CHANNEL BY A GERMAN SUBMARINEToList
Accordingly the air must escape through existing holes, as the water pouring in drives the air into the hold; the pressure with which the water comes in is equal to the air pressure in the hold. It is quite conceivable that a cargo may be so closely packed that there will be no space left for air to escape, but this is hardly ever the case; frequently, however, the cross-sections of the air vents are so small that the air escapes only very slowly, and the water enters very slowly in the same ratio; under these conditions it would take a long time for a ship to sink. This undoubtedly is very desirable in peace time, but in time of war this is not at all agreeable to our purpose; first, ifthe foundering of the vessel is prolonged we are prevented from accomplishing other work, and secondly, warships may come to the assistance of a sinking steamer.
Whenever possible we found it expedient to break open with an axe big holes in the lockers in case the hatch could not be quickly enough removed; or, if circumstances did not permit of our doing this, we shot holes with our cannon into the upper part of the steamer, above the hold, so that the air might conveniently escape and the water rush in. We employed, with excellent results, this method in the sinking of many steamers which otherwise would have settled too slowly.
It happens sometimes that a ship may carry a cargo that floats and that is not porous, such as wood. It isimpossible to sink a vessel with such a cargo by admitting water into the hold. Shots therefore must be fired at the engine and boiler rooms to force this kind of a steamer to sink. In general this is a safe rule to follow, for these are always the most vulnerable portions of every heavily laden vessel, and this mode of attack is nearly invariably successful.
A warship is usually equipped with cross or lateral bulkheads, in addition to the longitudinal bulkhead that runs from stem to stern through the middle of the ship, dividing it into halves, and other bulkheads separate these two longitudinal sections into further subdivisions. With the exception of the great fast passenger steamers, these divisions by means of longitudinal bulkheads seldom exist on vessels ofcommerce, although exceptions are to be found.
The sinking of a steamer with a multitude of partitions is effected by its gradually listing more and more on the side in which the water is penetrating, until it capsizes completely and founders with the keel uppermost. A ship can also roll over on its side as it plunges downwards with stem or stern erect.
Theoretically a vessel might sink on a parallel keel, descending horizontally deeper and deeper into the sea; but it never occurs in reality. This hypothesis assumes that a ship has taken in at the bow exactly the same amount of water as at the stern, at exactly the same distance from the center of gravity; this, of course, is impossible; besides the holes through which thewater is pouring in must also be at precisely the same level, or else the water pressure would be greater at one end than at the other, and the slightest alteration of level would occasion a greater intake of water and upset the equilibrium of the boat.
There is one other point I will touch upon; it has often been asserted, especially in romances of the ocean, that as a ship sinks the suction creates a tremendous whirlpool which engulfs all things in its vicinity. This statement is naturally very much exaggerated. People swimming about may be drawn down by the suction of the foundering ship, but in my opinion no lifeboat which is well manned is in danger of this whirlpool. Even old sailors, deluded by this superstition, have rowed away in haste from asinking ship, when they might have stood by and saved many lives.
The question is now often being put, whether it will be possible to raise the vessels that have been sunk during the war. The raising of a ship depends above all upon whether the depth at which it lies is so great that it precludes the work of a diver.
I have already stated that the water pressure augments at the rate of one atmosphere (one kilogram to the square centimeter) to ten meters' increase of depth. If a diver working at ten meters' depth is under a pressure of one atmosphere, at fifty meters he will be under the tremendous pressure of five atmospheres. This is the greatest depth to which a diver can attain, and if by chance a diver has gone a few meters beyond fifty meters, no man tomy knowledge has attained sixty meters. The work of divers at a depth of forty or fifty meters is even then not very effective, as they are unable to perform heavy tasks, nor can they remain more than half an hour at a time under such a pressure, and I am speaking now only of experts; therefore only light and easy work can be performed by most divers at a great depth and the appliance of ponderous chains for lifting purposes can only be accomplished under unusually favorable conditions. To raise any ship at a depth above thirty meters must be considered as a very efficient job, whereas if this is attempted at a depth below thirty meters it can be done only by salvage companies where neither unfavorable bottom obstacles nor currents intervene. A strong currentrenders a diver's work impossible, for it carries him off his feet.
On the high seas the currents change with the ebb and flood. At the precise moment of the turn of the tide the undercurrent is supposed to be nil, and the diver must take advantage of this moment to perform his task. Another difficulty arises from the sand being shifted by the currents, and settling on the prominent parts of a wreck; it often envelops them to such a degree that the ship becomes so deeply embedded in the sand that it is no longer salvable.
According to my estimation eighty per cent of our enemy's sunken ships lie from fifty to a hundred meters below the surface of the sea, so that all possibility of their being raised is excluded. The largest ships nowadays have adraft of less than ten meters, and as the vessels sunk lie at far greater depths they are no source of danger to shipping in time of peace. Of the remaining twenty per cent of sunken ships half of them are unreclaimable, either owing to their position, or owing to the high cost of salvage, or because it is not even known where they lie. The other half or last ten per cent have probably for the greater part been sunk in channels where the currents are so swift that they are covered with sand, and diving enterprises are out of the question. In time of war such work cannot be thought of; after the war the ships will long since have been completely buried by the sand.
Maybe off the east coast of England one or two ships may be raised, for they lie at a lesser depth and areexposed to slighter currents than on the south coast of England, but in that district only the smaller and more insignificant vessels have been sunk, and it would hardly pay to raise them, especially as they are so damaged by torpedoes and mines that they would probably fall apart on being raised to the surface.
Therefore hardly a single ship will be salvaged, and the sea will retain all those ships it has swallowed in the course of this war carried on by all the nations of the earth.
Typographical errors corrected in text:Page 1: VAN FORSTNER replaced with VON FORSTNERUnusual words:Page 134: salvable (adj.) means that can be salvaged or saved
Typographical errors corrected in text:
Unusual words:
In Introduction, page xxi, line 6 from the bottom, for "1915" read "1916."