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 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.
[Illustration: Courtesy of _U. S. Navy Department_
Below the water line this ship is divided into 500 water-tight
compartments.
THE UNITED STATES BATTLESHIP KANSAS]
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.
[Illustration: Courtesy of Robinson's "Naval Construction"
HOLD PLAN.
INBOARD PROFILE.
These drawings show the minute subdivision of a battleship. Below the
protective deck (shown by heavy line) the hull contains 500 water-tight
compartments.
PLAN AND LONGITUDINAL SECTION OF THE BATTLESHIP CONNECTICUT]
The double-skin construction, which was used 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.
[Illustration: 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.
[Illustration: 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 LIES IN SUBDIVISION]
"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 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.
[Illustration: 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]