Part 15 (2/2)
Under each side of the s.h.i.+p and upon the launching ways there is built a timber framework capable of raising the s.h.i.+p bodily off the blocks upon which until now it has reposed. These two frames, being connected together by chains pa.s.sing beneath the keel, const.i.tute what is called the cradle, the ”toboggan” which is to slide down the ways, bearing the s.h.i.+p upon it.
It is easy to see that being top-heavy something must be done to give the s.h.i.+p support before the sh.o.r.es on either side can be taken away, and it is equally clear that these latter must be removed before she can slide down to the water. Neither would it do to let the vessel slide upon her own plates, so we see that the cradle fulfils a twofold purpose, first enabling the s.h.i.+p to reach the water without ripping holes in her own plates, and secondly giving it the necessary side support to prevent it from toppling over on the way.
When all is ready, but a short time before the hour appointed for the launch, a curious operation is performed. Between the main part of the cradle and the part which actually slides upon the ways wedges are inserted, hundreds of them, and they are all driven in simultaneously.
Their purpose is to make the cradle slightly higher and so to lift the s.h.i.+p off the blocks upon which it was built. If they were driven in one at a time each would only dig its way into the timber and nothing else would happen, but being driven all together a most powerful lifting action is produced which actually raises the mighty s.h.i.+p. So hundreds of men stand, each with his hammer ready to strike a wedge, while the foreman stands by with a gong. At a stroke on the gong the hundreds of hammers strike as one, and so the s.h.i.+p is raised off the blocks, which can then be removed, to facilitate which they too are built of wedge-shaped pieces which can easily be knocked apart. The sh.o.r.es, too, have ceased to serve any useful purpose and can be taken away until at last all sh.o.r.es and all blocks are gone and the vessel rests upon the cradle only. Meanwhile tons of grease have been put on the ways, and the s.h.i.+p, urged by its own weight, is straining to get down the greasy slope into the element for which all along it has been intended. At this stage the only thing which restrains it is a kind of trigger arrangement on either side which locks the cradle in its place. In some yards elaborate mechanical catches controlled by electricity are used for this, but in many the old device of ”dog sh.o.r.es” is still used. These are simply two stout wood props which fit between a projection on the ways and one on the cradle, there being one dog sh.o.r.e on either side. Just over each dog sh.o.r.e there hangs a weight.
The person who performs the ceremony cuts the cord which holds the weights, the weights fall, the dog sh.o.r.es are knocked away, and the s.h.i.+p is free. Slowly at first, but gathering speed every moment, she moves majestically downwards into the water, being ultimately brought to rest by means of chains.
Whether done by the simple dodge of cutting a cord or by the more refined method of pressing an electric push, the launching is generally preceded by the breaking of a bottle of wine against the bows and the p.r.o.nouncement of the vessel's name.
Once safely afloat, the vessel is towed away and berthed alongside a wharf whereon are cranes and other machines which lightly drop on board of her the ma.s.sive turbines and boilers which in time will propel her, and the guns with which she will fight. All the mult.i.tudinous little finis.h.i.+ng touches are here put into her until at last she sallies forth on her trial trips to show what she is capable of, after which follow trials of her guns, and then she takes her place in the fleet.
Thus, briefly sketched, we see the history of the wars.h.i.+p from her inception in the minds of her designers till she is ready to meet the foe.
CHAPTER XVIII
THE TORPEDO
In parts of South America there lives a little fish, which, if you touch its nose, gives you a severe electric shock. The natives call it the ”torpedo.” When an artificial fish came to be invented, capable of giving a very nasty shock to anyone touching its snout, that name was bestowed upon it too.
Even more than the submarine, the torpedo resembles a fish with its graceful outlines and its fins and tail, the chief difference being that the tail of the torpedo carries a couple of little rotating propellers.
Looked at another way we may say that the torpedo is an automatic submarine. As a matter of fact, we all know it best as the weapon of the submarine.
It was originally invented by an Austrian who took it to a Mr.
Whitehead, an Englishman who then had an engineering works at Fiume.
This gentleman took up the idea and developed it into the Whitehead torpedo, which is to-day used by half the navies in the world, the rest using something very similar. It is curious to note that the German variety is called the Schwartzkopf, the meaning of which is ”blackhead.”
The smooth, steel, fish-like body consists of two separate parts, which can be detached from each other. The front part called the ”head” is made in two kinds, the war-head and the peace-head. The former contains a large quant.i.ty of explosive and the mechanism for firing it on coming into contact with any hard body. It is only used in actual warfare. The peace-head is precisely the same shape and weight as the other but is quite harmless, so that when it is fitted to the torpedo the latter can be handled with perfect safety, a valuable feature during the frequent exercises through which our sailors go in their efforts to attain perfection in the use and handling of these valuable weapons.
So much for the head. The body of the torpedo contains a beautiful little engine precisely similar to a steam-engine but on a small scale, which is driven by compressed air, a store of which is carried in a compartment provided for the purpose.
Then there is an automatic steering apparatus controlled by a gyroscope, the purpose of which is to keep the torpedo steered in precisely that direction in which it is started. If any outside force, such as current or tide, deflects it from its path the gyroscope, acting through a rudder at the tail, brings it back again.
Like the submarine, moreover, it has rudders which can steer it upwards or downwards and these again are controlled automatically so that having been set to travel at a certain depth the torpedo can be launched into the water with the practical certainty that it will descend to that depth and then maintain it.
This remarkable result is attained by the use of two devices acting in combination, namely, a hydrostatic valve and a pendulum. Either of these alone would set the thing going by leaps and bounds, at one time above the required depth and at another equally below it, and so on alternately. The hydrostatic valve consists of a flexible diaphragm, one side of which is in contact with the water outside, so that since the pressure increases with increasing depth, it is bent inwards more or less as the depth varies. This deflection is made to control the horizontal rudders. Suppose that things are adjusted for the rudders to steer the torpedo horizontally when at a depth of ten feet: if it descends to twelve feet the increased deflection of the diaphragm will so change the rudders that they will tend to steer slightly upwards: if, on the other hand, it rises to eight feet the contrary will happen, with the result that it will descend. As has been said already, this alone would result in a continually undulating course, so the pendulum is introduced to check the too decided changes in direction and so produce a practically straight course.
There is an interesting feature, too, about the propeller. It is ”twin”
but not, as in s.h.i.+ps, two screws side by side. Instead, they are both set upon one shaft or rather upon two concentric shafts, like the two hands of a clock. The hour-hand of a clock is on one shaft, a solid one, which itself turns inside the shaft of the minute hand, which is hollow. The propellers of the torpedo are likewise, one on a tubular shaft and the other on a solid shaft inside it. These two shafts turn in opposite directions, but since the two propellers are made opposite ”hands” they both equally push the torpedo along. The reason for this arrangement is that without it the action of a single propeller would tend to turn the torpedo over and over. Instead of the torpedo turning the propeller the propeller would to some extent turn the torpedo.
The range of the torpedo depends, clearly, upon the quant.i.ty of compressed air which it is able to carry and that is limited by certain practical considerations. One of these is the s.p.a.ce required to store it, and a very ingenious method has been invented whereby the limited supply is eked out so that in effect its quant.i.ty is increased. As the air is used up the pressure in the air-chamber naturally falls and when that has gone on to a certain extent chemicals come into action which generate heat, whereby the remaining air is raised in temperature. This, of course, increases the volume of air and the result is just the same as if a greater quant.i.ty were carried to commence with.
The explosion is brought about by the pressing in of a pin which normally projects from the nose or point of the torpedo, and it would be very easy to knock this accidentally, causing a premature explosion, were not precautions taken to prevent it. These take the form of a little fan which is turned by the water as the torpedo proceeds through it. The firing-pin is locked by means of a screw so that it cannot be operated until it has been released by the withdrawal of the screw and that can only be done by the fan. Thus, while on the submarine or whatever s.h.i.+p carries it, the torpedo cannot be fired: it only becomes capable of explosion after it has pa.s.sed through the water for a certain distance, far enough, that is, for the fan to have undone the screw.
Thus the maximum of safety is combined with the maximum of sensitiveness when the object aimed at is struck.
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