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 a sinking 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 to my 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 current renders 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 a draft 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 are exposed 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.