On Floating Batteries - |
A Lecture given by Captain Fishbourne, R.N.,
on Monday 19 April 1858,
as reported in the United Services Institute Journal Vol II, 1858.
AT an Evening Meeting it is not desirable to attempt more than touching on the important points involved in the question of Floating Batteries; but, in doing so, it is impossible to pass without notice those constructed by the French for service in the late war with Russia., together with those constructed for our own government.
They differ so much in form from ordinary vessels that it is difficult to institute a comparison, but this may safely be affirmed that they very widely depart from correct principles.
No one who had sufficiently considered the subject could have supposed otherwise than that they would have been most difficult to navigate, of very limited utility, and would, under some circumstances, be unsafe. The results obtained from those employed at Kinburn, the only occasion on which any of them have been tried, are not sufficient to warrant the many sacrifices of number of guns, of form, &c., necessitated by the great weight of their iron casing, if it does not also show that their form was not their least defect.
It would appear that in the fort at Kinburn which the three French floating batteries engaged there were but thirty guns, of which number perhaps not more than ten were opposed to them, while the French batteries were supported by the Odin, which vessel was able to fight ten guns on the broadside, two of which were large pivot guns, also by eleven gunboats and by mortar-vessels. Yet so comparatively incomplete was the protection of the iron casing, and so comparatively ineffective the firing from the shipping, that they had a far greater proportion of men placed hors de combat than were so in the fort, though it was subjected to an enfilading fire from various quarters.
Thus the number of men placed hors de combat in the shipping amounted to one for less than three guns in the various forts engaged, while the number placed hors de combat in the forts amounted only to one for every four guns in the ships.
The number of guns employed by the Allies appears to have been eight times those employed by their opponents, yet the number of injuries inflicted by the former was only five times those inflicted by the latter.
It may fairly be affirmed that a large proportion of the injuries which occurred to the Russians were caused by riflemen placed in galleries on the unengaged side of the floating batteries, more particularly as the former were much exposed, owing to their guns, or many of them, being mounted en barbette.
And, when the further disadvantageous circumstances under which our opponents were placed are considered, the conclusion that there was something radically wrong will seem inevitable. Thus their guns were but 18 and 32 pounders, while ours were 32, 50, and 68 pounders. Nor did their forts afford much protection, as they were in a "neglected state," or composed of "slight earth and basket-work." And, while their fire was necessarily divergent, ours was convergent and enfilading.
In these remarks I would be understood rather as giving unqualified praise to the gallantry and endurance of the defenders, than as depreciating the services or the skill of our officers and men, or those of our ally. I apprehend that there was no deficiency in either respect to account for what occurred; we must, therefore, look elsewhere for an explanation.
The floating batteries having. been anchored at about six hundred yards' distance, were they not very different from other ships, we should have been warranted in expecting more satisfactory results from their fire; and, therefore, that they were not more effective must have been in a great measure because their form was so defective. A discussion of the consequences of their peculiarity in that respect will lead to the conclusion that no better results could reasonably have been expected.
Their dimensions varied little from the following: Length 180 feet, breadth 48 feet, draught of water 8 feet. Fig. I. represents nearly the greatest cross section of one of them.
Suppose then a b f e to represent that. cross section when the vessel was upright, and that it is situated on a rigid horizontal plane p l ; suppose also that section to be rolled on that plane through the angle x y z, say equal to 10° ; in that case a b and f will move to a' b' and f' respectively, and c, the centre of gravity, will be raised to c'.
It will be perceived from this figure that in this and corresponding forms the rise of c will be proportional to the angle of inclination, and in any form the rolling of which occasions a rise of c the amount will be in proportion as e t is longer than t c the shorter axis; the motion of c is analogous to that of the centre of an eccentric wheel when rolled on a rigid horizontal plane.
Suppose now the force that inclined Fig. I. to cease acting in the original direction, to be removed to the other side of the figure, and to act in an opposite direction, c' will then fall towards c with all accelerated velocity proportional to the space fallen through, and, acting to produce a similar direction of rotation with that of the inclining force, will carry c to a greater height on the other side of the perpendicular; but this rise involves a greater subsequent fall, and consequently a still greater acceleration, producing a motion analogous to that of a child's rocking-horse, the merit of which is, that it possesses a quality that tends to perpetuate any motion communicated to it, but which is one least to be desired in a platform for guns, where rest is indispensable for perfect precision of fire.
If, on the contrary, we roll a vessel whose sections are similar in form to that of Fig. II. owing to the fact that all parts of the periphery
are equidistant from the centre of rotation, there would not be any rise of the centre of gravity c, except of course the trifling quantity shewn by the position of c', which arises from the centre of gravity being below the centre of rotation, but which takes place only in common with vessels of the form of Fig. I. in addition to the very great rise produced by the causes previously described.
It will be affirmed that water is not rigid, and that therefore these results do not occur ; no doubt this is in part true, but water resists, with great force, any effort to give a body rapid motion through it, and to that degree it acts as though it were rigid, and from that cause produces effects similar to those described, differing only in their amount.
But effects such as those described occur to ships at sea for another reason, and that is because the inclining forces are waves and hollows that are alternately above and below the mean level, and act alternately on one side or the other of any ship that may be afloat amongst them; consequently motion is communicated in an amount, greater, as the half-breadth is greater than the immersed depth.
Consequently the motions of the iron-cased batteries in question must necessarily have been rapid and extensive from the causes above described ; their defects would have been aggravated by their small draught of water, which, while it assimilates their motions to those of short. pendulums, deprives them of the advantage of the resistance to quick rotation offered by depth of immersion.
A further injurious effect would arise from the concentration at the sides of the weight of the iron casing, as by its inertia it would in the first instance resist inclination ; the sea therefore would break into the ports when they were open ; then again, when motion was communicated from the inertia, it would be continued too long. From all which it is evident that no precision could be obtained from such vessels at any time that the water was disturbed, which appears to have been the case at Kinburn, as the attack was delayed for two days owing to the swell, which it was said would have occasioned a great loss of ammunition had they opened fire.
The French Admiral seems to admit that their floating batteries were not very effective, for he considered that it was the vertical fire which most contributed to the capitulation.
The form of the floating batteries used at the siege of Gibraltar, prints of which are preserved in the topographical department of the United Service Museum, is in marked and favourable contrast to those with iron casing, whether French or English ; and approaches nearly to that of Fig. III. of which I was not aware until after I had written this paper.
The older forms of the French and Spanish architects were not adopted without much experience and mathematical knowledge, and we did not act wisely or reasonably in departing so widely from them. The following is a cross section of one of the batteries employed against Gibraltar:-
So much for form ; but the greater or less efficacy of iron casing, as shown at Kinburn, deserves further consideration. Thus many shot struck vessels thus sheathed without penetrating their sides, but it must be observed that these were fired from guns of comparatively small calibre, and the distance was considerable ; that is to say, it was quite beyond breaching distance even for a land battery, and still more so for a battery afloat, subject to motion and its consequent effect in preventing precision of fire. Further, it is to be presumed, from the neglected state of the fortifications, that neither the guns, powder, or shot were by any means equal in quality to those of the Allies, and it is probable that, arising from this, the shot were deficient in penetrating power.
It is a remarkable fact, that the very great proportion of the injuries to the personnel in the French squadron occurred to those on board iron-cased ships, and there is ground for the supposition that this would have been much greater if the Russians had had some disposable riflemen to have returned the fire of the French riflemen, and to have picked off the crews of their ships through the portholes.
And there can be no reasonable doubt, had the calibre of the Russians' guns been equal to those in the floating batteries, but that the crews of the latter would have suffered severely from the splinters that would have been thrown off from the framework supporting the iron plates by the violent concussion of their heavy shot on their sides.
The question of metal-casing ships involves so much that it ought to receive a full and calm discussion. Thus, should it prove practicable to build efficient sea-going iron-cased ships, many of our large and expensive wooden ships would be superseded in most of the immediate purposes of war; and, though I am strongly impressed with the belief that the practice of effectually casing ships with iron, without otherwise materially impairing their efficiency, is surrounded with greater difficulties than are imagined even by those who have given the most intelligent consideration to the subject, I am still more strongly impressed that no one has more than a distant conception of what naval tactics will become in consequence of the introduction of steam, combined with rifled guns and improved gunnery.
To revert to the subject of the difficulties of iron casing. Take the case proposed in the House of Commons, that of cutting down a three-decker and coating her with iron plates - say the Duke of Wellington. This would involve taking an aggregate weight of, say 1,000 tons, from heights above the existing centre of gravity, varying from 12 to 33 feet, and placing an equivalent weight in the form of iron casing at a mean height of the load water-line ; this, supposing the total weight of "the Duke " to be 6,000 tons, would lower her centre of gravity upwards of three feet, of the effect of which on her motions it is nearly impossible to give more than a faint idea - it would at least produce an extraordinary rapidity of motion.
We all know how much ease is often given to a ship by running her guns in, the weight of which in the Duke of Wellington may be about 200 tons, and the distance five feet : from this an estimate may be formed of the effect in a contrary direction that would be produced - 1st, by moving 1000 tons eight or ten feet further out ; 2nd, by moving the same 1000 tons a mean distance of twenty feet lower down.
If we assume that the Agamemnon at her builder's draught is comparatively easy - for which of course I cannot answer, but she is reported to be so, and I think it probable that she would be so ordinarily in a calm - we may form from her an estimate of the effect of the change proposed in the Duke. When the former started with the telegraphic cable she drew three feet more than her proper load draught, which it might easily be proved did not lower her centre of gravity more than from eighteen to twenty inches, or little more than half that proposed in the Duke, and yet we find that at times, "in a calm, with a beam swell, the paroxysms of rolling, to which she was subject, were such that there was great difficulty in doing anything but hold on during them;" how far this will consist with fighting any, much less heavy, guns, I must leave my reader to decide.
We will suppose a metal-cased vessel broadside to the sea, and her opponent can always force her into that position ; her stability will be such that she will not yield to the sea when first it reaches her side, consequently, if her ports are open, the sea will break into them in quantities proportional to their less or greater height above the mean level ; it is impossible, however, but that she must yield, to accommodate herself to the altered plane or surface of the sea, as the wave rolls across towards a vertical plane passing through her centre; she will do so then rapidly, and, when the sea has passed the centre line, the action of the wave and that of the altered weight will cause her to recover herself with a rapidity proportioned to her increased stability ; this will be so rapid as to make it impossible for men to stand, still less to work heavy guns, except in the smoothest water, besides risking the masts.
Nor does the evil end here, for the great concentration of weight at the sides would act like that in a fly-wheel, and, though the oscillations of the ship should commence concurrently with those of the sea, the momentum of the sides would carry them through longer arcs, and establish oscillations that would not synchronize with those of the wave, from which the ports could be open but seldom ; and, when there was a concurrence of oscillations of wave and ship, the subsequent rolls of the ship would be very dangerous from their extent and rapidity.
The more extensive the arcs rolled through, the greater must be the depth and weight of iron casing if the ship is to be protected at her most vulnerable point, viz., between wind and water, and thus the protection establishes a necessity for a greater extent of sheathing.
It may readily be seen that, the broader a vessel is, the greater depth of casing she must receive, as the greater the breadth the greater is the extent of side subtending a given angle.
Thus the difficulties of attaining complete success are little short of insurmountable; but let it be granted that the greater portion of them may be overcome, that we may proceed to consider how far such vessels are likely to be brought into general use.
1st. Against shore batteries.- For the present it may be granted that the iron casing affords equal protection with anything which can be applied on land, but, to obtain it, two-thirds or three-fourths of the number of guns, as compared with the number in other ships, are sacrificed ; obviously, then, such a vessel would require to be three or four times the length of time employed by an ordinary ship in effecting a breach ; furthermore, against a battery, the upper and main-deck guns of two and three deck ships are often most effective, owing to their greater height giving command over the parapet.
2nd. Against ordinary ships.- Let it be assumed that shot will not penetrate the iron casing; for the most part then they will be only vulnerable through their ports.
1. Then the greater number of guns and the greater precision of fire which is certainly attainable in an uncased ship would make her a dangerous competitor, particularly if she closes; for, though she cannot pierce the side, she will certainly make the wood framing splinter, and thus do nearly as much damage.
2. An iron-cased ship cannot have fine lines, consequently an uncased ship can always be built to be faster either by steam or sails ; the latter then may choose her distance or time of attack, or whether she will engage at all. The probability is that such ships will have masts and sails very disproportioned to their great weight, in which case they will sail but indifferently; and it is also probable that they cannot be constructed to carry more than a small proportion of coals, which would be a further defect.
It is too generally overlooked that effective fire is the best defence, because it destroys the enemy's means of attack ; now the only chance a ship has against a battery is that derived from her power of concentrating a large number of guns on a few, and of pouring in a torrent of fire that overturns guns or drives the men from them ; these advantages are abandoned in the iron-cased ship, and the increased time such a vessel would be under fire would enable those in the battery, either by rifles, or by the greater precision of their "great" guns, always obtainable in shore practice over ship, arising from the motion of the latter, to place the crew of the iron cased ship hors de combat, either through her ports or by a continued fire of the latter breaching her side.
But the question arises, Are we justified in admitting that metal casing will resist large-sized solid shot ? and, though it did, it must be borne in mind that the concussion of such would be so great, that the wood framing carrying the casing would be splintered perhaps more than if the shot penetrated.
Again, floating batteries must have large guns if large guns are opposed to them; and then they must have large ports, owing to which they would be proportionably more vulnerable.
But there is much room for the supposition that cylindrical or conical shot from rifles and guns will penetrate any casing which it will be practicable to apply.
These circumstances, when taken in connexion with the facts that the men in all vessels are collected close to the unprotected parts, such as the ports, and the little precision attainable from great guns at 1000 yards in any floating battery that has been built, as compared with the precision which is attainable from rifle musketry and from shore batteries, suggests doubts as to the propriety of our embarking any large sum in building such vessels without first making some well-devised experiments.
That other nations have done, or are doing so, is no sufficient justification, unless we know or have a well-grounded belief that they are acting wisely. We in some measure copied the French batteries alluded to, but we might have built far more effective batteries, at much less expense, and in sufficient time for them to have taken part in the hostilities.
On the other hand, it should be stated that the greater speed and greater fitness for making long passages attainable in the wooden ships would enable them to relieve colonies, or do infinite damage without hindrance from metal-cased ships, which alone would seem sufficient to establish that the latter never could be extensively used.
Nevertheless, it is manifest that floating batteries suited for service in shoal water, that would still be efficient gun platforms, are much required.
Sir George Sartorius proposed rafts for this purpose, as did also General Wavel, who further suggested that such should be built of the wood of which the balsas (rafts) of Guayaquil are made; these are merely balks of timber of very small specific gravity, lashed together, with a platform and hurricane-house in the centre, and propelled by sails.
This is very simple and efficacious, and could be readily put together with rapidity. I should contemplate rafts upon a much larger scale, to be driven by steam, and formed of iron on a cellular system. They would possess many advantages, and their form would obviate many disadvantages which could not be avoided either in other descriptions of floating batteries or in ships.
For, 1. If speed be so important as is supposed by many, greater speed could be obtained from such than from any other description of vessel.
2. The cost of their construction would be much less, while the facility of constructing them, and therefore their rapidity, could be much greater.
3. The precision of fire possibly from them would be so much greater that the effectiveness of their guns may be estimated as 6 to 1 of those in any other description of vessel, while, from the cellular system of construction, they would be much less vulnerable, they would be much less subject to being hit, as a very large proportion of the shot that would hit a ship would pass over them.
4. They could be used for attack in shoal water, or could retire to shoal water for protection against ships ; they could be used to embark, disembark, and protect a landing of troops, or used to move masses of men along shore with rapidity; they could be employed to form a necessary complement to shore batteries, by being placed where neither the latter nor ships could be.
5. They could always obtain shelter from bad weather, and would not require to be placed in docks for repair.
The precision of fire that might be attained from such results, as compared with any other description, would be something extraordinary :the value of which, in a mere commercial point of view, may in part be perceived by the facts related with reference to an attack of the French on Vera Cruz - of 311 shells that were fired, only three hit, and only 17 per cent. of the shot struck, though the distance was but 1,200 yards. They might be fitted with iron parapets considerably retired from their extremities towards their centres, of sufficient strength to resist almost any description of shot, and with nettings to prevent their being boarded without great difficulty; and, when employed as an addition to shore batteries, they might be surrounded by small piles, to protect them more effectually against boat attacks.
I am fully convinced that it is on the principle described that our coast defences in general should be constructed, while for some purposes of defence by attack they would be unequalled.
Their construction being elaborately cellular, they could hardly be so extensively injured as to be sunk, and, as they would not offer more than an inconsiderable vertical surface, it would be almost impossible to hit them, except when close; and, their guns being a fleur d'eau, nothing would be too low to escape the effects of their horizontal fire, the range of which might be usefully extended by the introduction of rifled cannon.
It was a grave mistake that the Baltic Fleet was not furnished with mortar-vessels and gunboats of this description ; a glance at the charts of that sea will show that such were indispensable to success, and with them half that fleet would have been much more efficient.
Chairman.- We shall be glad to hear any remarks that any gentleman may have to make upon the lecture which Captain Fishbourne has been kind enough to give us; and he I am sure will be very happy to answer any questions that any gentleman may think it right to put to him upon the subject.
Captain Ryder, R.N.- I wish to state that I saw the effect of these batteries at Kinburn, and I do not agree with Captain Fishbourne in speaking so lightly of the use of iron batteries. I rode round immediately after the action and observed sixty distinct marks from round shot. In the French batteries only two men were killed, although they were under fire for more than an hour within six hundred yards of the shore batteries. The floating batteries used at Gibraltar must have drawn 18 feet water.
Captain Fishbourne.- True two only may have been killed, but a very much larger number were placed hors de combat, and, though some of their wounds may have been slight, they showed their exposure and the incompleteness of the protection afforded by the iron casing.
Captain Ryder.- I do not suppose that any advocate of iron casing would say that it did more than diminish the effect of shot. I saw the effect on the shore batteries, and that there was no vestige of stone left on those parts that were opposed to the floating batteries ; here was nothing but rubble.
Captain Fishbourne.- This does not argue much effect, for Lieut. Dahlgren, after giving quotations from the official reports on the state of the fortifications, adds, "Considering the importance of excluding an enemy from the basin of the Dnieper, some surprise may reasonably be excited at the feebleness of the defences which were to command the entrance."
Major Jervois.- I think it may be said generally that we are not by any means able at present to determine what resistance we may expect from iron if adopted generally, either on land or at sea, or whether it will afford an effectual protection to those behind a parapet or bulwark. Experiments are now in course of being made at Woolwich and elsewhere, with a view to determine that question.
Mr. Geo. Rennie, C.E., exhibited a model of a floating battery, somewhat similar in form to a Martello tower, from the sides of which, owing to its circular form, he considered shot would be turned off. He proposed the application of a screw for the purpose of propulsion, and a double keel to ensure that the motion given should be in a linear direction.
That gentleman also exhibited a model of a gun-boat which he had designed for police service on the rivers in India. It is fitted with a gun on Dahlgren's principle, capable of being given an entire revolution, and is raised and lowered by a screw. Some boats of this class have been built for the East India Company.
Chairman.-Mr. Rennie, have you submitted your plan to the India House authorities, or to those at the Board of Control ?
Mr. Rennie.- No; you are the first person who has seen it.
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