WARSHIP PROTECTION AGAINST RAM, MINE, AND TORPEDO
The most perfect example of protection by subdivision of the hull into separate compartments is to be found in the warship. It is safe to say that there is no feature of the design to which more careful thought is given by the naval constructor than this. Loss of stability in a naval engagement means the end of the fight so far as the damaged ship is concerned. Nay, even a partial loss of stability, causing the ship to take a heavy list, may throw a ship's batteries entirely out of action, the guns on the high side being so greatly elevated and those on the low side so much depressed, that neither can be effectively trained upon the enemy. Furthermore, deep submergence following the entrance of large quantities of water, will cut down the ship's speed; with the result, either that she must fall out of line or the speed of the whole fleet must be reduced.
In the battle of the Sea of Japan it was the
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Courtesy of U. S. Navy Department
Below the water line this ship is divided into 500 water-tight compartments.
The Unites States Battleship Kansas
bursting of heavy 12-inch shells at or just below the water-line of the leading ship of the Russian line that sent her to the bottom before she had received any serious damage to her main batteries. Later in the fight, several other Russian battleships capsized from the same cause, assisted by the weight of extra supplies of coal which the Russians had stowed on the upper decks above the water-line.
In the matter of subdivision as a protection against sinking, there is this important difference between the merchant ship and the warship, that, whereas the merchant ship is sunk through accident, the warship is sunk by deliberate intention. The amount of damage done to the former ship will be great or small according to the accidental conditions of the time; but the damage to the warship is the result of a deliberately planned attack, and is wrought by powerful agencies, designed to execute the maximum amount of destruction with every blow delivered.
A large proportion of the time and money which have been expended in the development of the instruments of naval warfare has been devoted to the design and construction of weapons, whose object is to sink the enemy by destroying the integrity of the submerged portion of the hull. Chief among these weapons are the ram, the torpedo, and the mine. There can be no question that the damage inflicted by the ram of a warship would be far greater, other things being equal, than that inflicted by the bow of a merchant ship. The ram is built especially for its purpose. Not only is it an exceedingly stiff and strong construction; but it is so framed and tied into the bow of the warship, that it will tear open a long, gaping wound in the hull of the enemy before it is broken off or twisted out of place. The bow of the merchant vessel is a relatively frail structure, and many a ship that has been rammed has owed its salvation to the fact that immediately upon contact, the bow of the ramming ship is crumpled up or bent aside, and the depth of penetration into the vessel that is rammed is greatly limited. Furthermore, because of its underwater projection, the ram develops the whole force of the blow beneath the water-line, where the injury will be most fatal.
Even more potent than the ram is the torpedo, which of late years has been developed to a point of efficiency in range, speed, and destructive power which has rendered it perhaps the most dreaded of all the weapons of naval warfare. The modern torpedo carries in its head a charge of over 200 pounds of guncotton and has a range of 10,000 yards. Ordinarily, it is set to run at a depth of 10 to 12 feet below the water; and should it get home against the side of a ship, it will strike her well below the armour belt and upon the relatively thin plating of the hull.
Most destructive of all weapons for underwater attack, however, is the mine, which sent to the bottom many a good ship during the Russo-Japanese war. The more deadly effects of the mine, as compared with the torpedo, are due to its heavy charge of high explosive, which sometimes reaches as high as 500 pounds. Contact, even with a mine, is not necessarily fatal; indeed the notable instances in which warships have gone to the bottom immediately upon striking a mine have been due to the fact that the mine exploded immediately under, or in close proximity to the ship's magazines, which, being set off by the shock, tore the ship apart and caused her to go down within a few minutes' time. This was what happened to our own battleship Maine in Havana harbour, and to the Russian battleship Petropavlovsk and the Japanese battleship Hatsuse at Port Arthur.
Enough has been said to prove that when the naval architect undertakes to build a hull that will be proof against the blow, not merely of one but of several of these terrific weapons, he has set himself a task that may well try his ingenuity to the utmost. Protection by heavy armour is out of the question. The weight would be prohibitive and, indeed, all the side armour that he can put upon the ship is needed at the water-line and above it, as a protection against the armour-piercing, high-explosive shells of the enemy.
Heavy armour, then, being out of the question, he has to fall back upon the one method of defense left at his disposal,—minute subdivision into watertight compartments. Associated with this is the placing at the water-line of a heavy steel deck, known as the protective deck, which extends over the whole length and breadth of the hull and is made thoroughly watertight.
The double-skin construction, which was used
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Courtesy of Robinson's "Naval Construction"
These drawings show the minute subdivision of a battleship. Below the protective deck (shown by heavy line) the hull contains 500 separate water-tight compartments.
Plan and Longitudinal Section of the Battleship Connecticut
to such good effect in the Great Eastern, is found in every large warship; and in a battleship of the first class, the two skins are spaced widely apart, a spacing of three or more feet being not unusual. The double-hull construction, with its exceedingly strong framing, is carried up to about water-line level, where it is covered in by the protective deck above referred to. Below the protective deck the interior is subdivided into a number of small compartments by transverse bulkheads, which extend from the inner bottom to the protective deck, and from side to side of the ship. The transverse compartments thus formed are made as small as possible, the largest being those which contain the boilers and engines. Forward and aft of the boiler- and engine-room compartments the transverse bulkheads are spaced much closer together, the uses to which these portions of the ship are put admitting of more minute subdivision.
By the courtesy of Naval Constructor R. H. M. Robinson, U. S. N., we reproduce on page 143 from his work "Naval Construction" a hold plan and an inboard profile of a typical battleship,—the Connecticut,—which give a clear impression of the completeness with which the interior is bulkheaded. Although the ship shown is less than one-half as long as the Titanic, she has 27 transverse bulkheads as against the 15 on the larger ship; and all but nine of these are carried clear across the ship from side to side.
Equally complete is the system of longitudinal bulkheads. Most important of these is a central bulkhead, placed on the line of the keel, and running from stem to stern. On each side of this and extending the full length of the machinery spaces, is another bulkhead, which forms the inner wall of the coal-bunkers. Forward and aft of the machinery spaces are other longitudinal bulkheads, which form the fore- and-aft walls of the handling-rooms and ammunition-rooms.
To appreciate the completeness of the subdivision, we must look at the inboard profile and note that the spaces forward and aft of the engine- and boiler-rooms are further subdivided, in horizontal planes, by several steel, watertight decks or "flats," as they are called. Including the compartments enclosed between the walls of the double hull, the whole interior of the battleship Connecticut, below the protective deck, is divided up into as many as 500 separate and perfectly watertight compartments.
Moreover, in some of the latest battleships of the dreadnought type the practice has been followed of permitting no doors of any description to be cut through the bulkheads below the water-line. Access from one compartment to another can be had only by way of the decks above. Furthermore, all the openings through the protective deck are provided with strong watertight hatches or, as in the case of the openings for the smoke stacks, ammunition-hoists, and ventilators, they are enclosed by watertight steel casings, extending to the upper decks, far above the water-line.
In the later warships, further protection is afforded by constructing the first deck above the protective deck of heavy steel plating and making it thoroughly watertight, every opening in this deck, such as those for stairways, being provided with watertight steel hatches. This deck, also, is thoroughly subdivided by bulkheads and provided with watertight doors.
It sounds like a truism to say that a watertight bulkhead must be watertight; yet it is a fact that only in the navy are the proper precautions taken to test the bulkheads and make sure that they will not leak when they are subjected to heavy water pressure. Before a ship is accepted by the government, every compartment is tested by filling it with water and placing it under the maximum pressure to which it would be subjected if the ship were deeply submerged. If any leaks are observed in the bulkheads, decks, etc., they are carefully caulked up, and the test is repeated until the bulkhead is absolutely tight.
Now, here is a practice which should be made compulsory in the construction of all passenger-carrying steamships. Only by filling a compartment with water is it possible to determine whether that compartment is watertight. To send an important ship to sea without testing her bulkheads is an invitation to disaster. The amount of water that may find its way through a newly-constructed bulkhead is something astonishing; for although the leakage along any particular joint or seam of the plating may be relatively small, the aggregate amount will be surprisingly large.
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Between the boiler rooms and the sea are four, separate, watertight walls of steel. The whole is covered in by a 3-inch watertight steel deck.
Midship Section of a Battleship
Let us now pass on to consider the actual efficiency of the watertight subdivision as thus so carefully worked out in the modern warship. Thanks to the Russo-Japanese war, which afforded a supreme test of the underwater protection of ships, the value of the present methods of construction has been proved to an absolute demonstration.
The following facts, which were given to the writer by Captain (now Admiral) von Essen of the Russian Navy, at the close of the Russo-Japanese war, and were published in the "Scientific American," serve to show what great powers of resistance are conferred on a warship by the system of subdivision above described. The story of the repeated damage inflicted and the method of extemporised repairs adopted, is so full of interest that it is given in full:
"Immediately after the disaster of the night of February 8th," when the Japanese, in a surprise attack, torpedoed several of the Russian ships, "the cruiser Pallada was floated into drydock, and the battleships Czarevitch and Retvizan were taken into the inner harbour, and repairs executed by means of caissons of timber, built around the gaping holes which had been blown into their hulls by torpedoes. The repairs to the Pallada were completed early in April, and about the 20th of June the Czarevitch and Retvizan were also in condition to take the sea. On the 13th of April, during the sortie in which the Petropavlovsk was sunk with Admiral Makaroff on board, the battleship Pobieda, in returning to the harbour, struck a contact mine, and was heavily damaged. Similar repairs were executed, and this ship was able to take her station in the line in the great sortie of August 10.
"On June 23 Captain von Essen's ship, the Sevastopol, was sent outside the harbour to drive off several Japanese cruisers that were shelling the line of fortifications to the east of Port Arthur. This she accomplished; but in returning she struck a Japanese mine, which blew in about 400 square feet on the starboard side, abaft the foremast, at a depth of about 7 feet below the water-line. The rent was from 7 to 10 feet in depth and 35 to 40 feet in length. The frames, ten in all, were bent inward, or torn entirely apart, and the plating was blown bodily into the ship. She was taken into the inner harbour, where the injured portion of the hull was enclosed by a timber caisson in the manner shown in the engravings on page 155. The caisson—a rectangular, three-sided chamber—was built of 9-in. by 9-in. timbers, tongued and grooved and carefully dovetailed. The floor of the caisson abutted against the bilge keel. The outer wall, which was at a distance of about 10 feet from the hull, had a total depth of about 34 feet, the total length of the caisson being about 75 feet. Knee-bracing of heavy timbers was worked in between the floor and the walls, and the construction was stiffened by heavy, diagonal bolts, which passed through from floor to outside wall, as shown in the drawing. Watertight contact between the edge of the caisson and the hull of the ship was secured by the use of hemp packing covered with canvas. The whole of the outside of the caisson was covered with canvas, and upon this was laid a heavy coating of hot tar. The caisson was then floated into position and drawn up snugly against the side of the ship by means of cables, some of which passed underneath the ship and were drawn tight on the port side, while others were attached to the top edge of the caisson and led across to steam winches on deck. After the water had been pumped out, the hydraulic pressure served to hold the caisson snugly against the hull. The damaged plating and broken frames were then cut away; new frames were built into the ship, the plating was riveted on, and the vessel was restored to first-class condition without entering drydock.
"On September the 20th, during operations outside the harbour, the Sevastopol again struck a mine, and by a curious coincidence she was damaged in the exact spot where she received her first injury. This time, however, the mine was much larger and it was estimated to have contained fully 400 pounds of high explosive. The shock was terrific and the area of the injury was fully 700 square feet. The ship immediately took a heavy list to starboard, which was corrected by admitting water to compartments on the port side. She was brought back into the harbour, and a repair caisson was again applied. The repairing of this damage was, of course, a longer job. Moreover, it was done at a time when the Japanese 11-inch mortar batteries were getting the range and making
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The battleship Sevastopol was twice struck by a mine; but she remained afloat and was repaired by the use of caissons without entering dry dock.
Safety Liens in Subdivision
frequent hits. One 11-inch shell struck the bridge just above the caisson and, when it burst, a shower of heavy fragments tore through the outer wall of the caisson, letting in the water and necessitating extensive repairs. Nevertheless, the Sevastopol was again put in seaworthy condition, this time the repairs taking about two and one-half months' time. During the eleven months of the siege of Port Arthur five big repair jobs of the magnitude above described were completed, and over one dozen perforations of the hull below water, due to heavy projectiles, were repaired, either in drydock or by the caisson method."
Now, when it is remembered that the Sevastopol was not a new ship, and that her internal subdivision was not nearly so complete as that which is found in the most modern battleships, it will be realised how effective are properly built bulkheads and thoroughly watertight compartments against even the most extensive injury to the outer shell of a ship. It is claimed for the latest battleships of the dreadnought type, built for the United States Navy, that they would remain afloat, even after having been struck by three or four torpedoes.
Now, it is inexpedient to build merchant ships with such an elaborate system of watertight compartments as that described in this chapter. Considerations of cost and convenience of operation render this impossible; but it is entirely possible to incorporate in the large passenger steamers a sufficient degree of protection of this character to render them proof against sinking by the accidents of collision, whether with another ship, a derelict, or even with the dreaded iceberg. The manner in which the problem has been worked out in several of the most noted passenger steamers of the present day is reserved for discussion in the following chapter.
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This ship has twenty-four compartments below the water line. Fire-bulkheads protect passenger decks.
The 65,000-Ton, 23-Knot Imperator—Largest Ship Afloat