Once a Week (magazine)/Series 1/Volume 3/The essentials of armoured ships
THE ESSENTIALS OF ARMOURED SHIPS.
The results of shot—rifled shot, fired point blank at the armour plates of vertical sided ships, have turned public attention strongly to the importance of slanting the sides both above water and below, to such an angle that the shot may glance from them. In Number lxvii. of this work, I explained, with a diagram, this theory, which the “Times” calls Jones’ system, and I since find that Mr. Jones has taken out a patent, dated November 1, 1859. Long before this date, my MS. of English War Ships and their Uses, was in the editor’s hands, and on November 19th (No. xxi.),[1] the second part was published containing amongst other things, these words:—
“In the application of this armour, the size of the vessel and amount of displacement become most important. The enormous weight has a tendency to make the vessel top-heavy, and to set her rocking. But weight matters little when size is great. And these iron walls should be made to slope inwards at an angle of forty-five degrees, in which case it would be difficult to strike a plate direct with a shot. It would glance off, and the sloping inward would remove overhanging weight.”
The diagram in No. lxvii.[2] is simply the same thing explained in detail.
Mr. Jones’ specification was published in due course, on the 1st May, 1860—my description on the 16th of November, 1859.
But let not my readers suppose that I lay any stress on the prior demonstration of so obvious a principle, long recognised in many modes, such as the glacis of forts, the slopes of sea-walls, and other structures. Whoever has looked at the midship section of an old-fashioned line of battle ship, will have remarked that the bottom is nearly a hemisphere, with a small ridge called a keel at the lowest part. Upwards from this hemisphere the sides “tumble in,” so that the batteries of the three decks present a profile sloping inwards, at an angle of some twenty-five degrees. The object of this was evident—to keep the centre of gravity well within the base, and prevent the weight of the guns from rendering the ship top-heavy. Where the “tumbling in” point ceased, about the level of the upper deck, the bulwarks were made to curve outwards after the fashion of machicolated towers, whether to obtain a “line of beauty,” or for the purpose of making sure of catching the enemy’s shot, does not appear; but probably the object was to prevent the sea washing up the sides and on to the decks. Some reason, good or bad, is at the root of all our apparent arbitrary forms, and this is the most probable one. Most antique vessels “tumbled in,” probably to keep their weight within the base, and so to make them steadier.
It has been objected to this proposition of sloping sides, that it affords great facility for running down, by forming an incline for the attacking vessel to mount on. This is not good mechanical argument. Running down, means a large vessel running over a vessel of inferior size. Whether the vessel’s bulwarks slope inwards or outwards makes nothing to the argument, inasmuch as the bulwarks in any case may be supposed to crush down to the level of the deck, and therefore it is the height of the deck above the water which determines the power of mounting on her deck by the attacking vessel in order to sink her. But in attacking by running down a vessel with a continuous knife-edge defence all round her, the attacking vessel must have the cut-water formed with an acute slope, the point rising above the knife-edge of the attacked vessel, or she might be in the very unpleasant predicament of going under instead of over the enemy, which would make all the difference.
We may fairly assume that a ship so constructed would be practically impervious to shot, Whitworth, Armstrong, or other, such as we at present possess; but, non constat, that a gun cannot be constructed to effect the object. A sixty-eight pounder, smooth-bore, can batter in the four and a half inch plates placed vertically, or at right angles to the gun, and with a shot weighing three cwt. the whole plate might be driven bodily through the side, as was the case with the thin plates exposed to light shot in the first constructed iron vessels.
But from the angle-sided ship the heavy shot, as well as the light, will glance off! Quite true as to ordinary forms of shot, but there is a process yet to be tried to prevent the glancing. If the shot be of hardened steel, and pointed to an angle considerably more acute than the angle of the iron plates, the point will enter, forming a fulcrum, and will thus obtain effect proportioned to the weight. There are two circumstances to consider in the plates; first, the power to resist penetration, or to cause glancing; and secondly, the area of bearing surface on the vessel’s side to prevent their being driven through. If, for example, the plates were only of a square foot in area, like so many paving-stones in a horseway, each might be driven through the side in succession. But if put in like the flag-stones of a foot-pavement in large surfaces, the resistance would be in proportion to the extent of surface. Therefore, it is clear, other things being equal, that the larger the plates, the more secure they will be.
In fact, the weak places are the joints and the bolt-holes. The bolts pass through the plates at right angles, and the bolt-hole is equivalent to a crack through the plate. Every heavy blow tends to loosen the fastenings, and with one plate burst out, the destruction of the plates in succession, and the ship’s side with it, becomes a comparatively easy matter.
Attempts have been made to improve the fastenings in two modes. One is to groove the edges of the iron plates all round, and in the grooves to place iron tongues, to keep them in even position with regard to each other. But it is evident that the act of grooving must weaken the plate very materially, and predispose it to break, weakening it where it is already weakest. The other method is to bolt to the ship’s side, in parallel lines, a class of iron bars, known on railways as foot-rails, forming thus a species of dovetails into which the armour plates are slidden. The bolts are thus hidden, but the fastenings through the metal are weak, and the probability is that the rails would be broken, and the plates would fall out.
There is one remedy for the difficulty, and, as it appears to me, but one. It is to make the plates continuous by welding them together at the joints, to form one solid skin. That this has not yet been done is no argument that it cannot be done, if only the government of naval affairs will set the right kind of people to work to do it.
Whatever sum of money may be spent in experiments, will be well spent if the end be accomplished. It is scarcely possible to estimate the value of a vessel of iron, an entire and perfect solid plate throughout. This more than any other is the essential point in iron vessels. It is scarcely a problem, and the means are within grasp. When this shall be done, England will be the mistress of the narrow seas, and no country will be able to compete with her in sea sovereignty; for she can afford to build three ships to the rest of Europe’s one, and so economise her sea-warriors, both in numbers and safety, at the same time as materially to lessen the annual cost in men, with less annual wear in vessels. When forms and proportions and construction shall be right, and iron dealt with in true fashion, the ordinary processes of destruction will be arrested, and ships at sea may be as durable as palaces on shore. And so long as England shall be a doer of justice, the moral sense of the world will uphold her physical power on the ocean. The perfection of her iron ships—her indigenous manufacture—is no mere creature of the imagination, but a practical fact to be accomplished by science.
- ↑ See vol. i p. 431.
- ↑ See p. 398.