|Title||Report: Iron Steam Battery [Stevens] 32nd Congress, 2nd session, HR, Exec. Doc. No. 23, Jan. 6, 1862.|
|Collection||Stevens Castle Collection|
|Credit||Museum Collections. Gift of a Friend of the Museum.|
|Scope & Content||
IRON STEAM BATTERY. Letter from the Secretary of the Navy, transmitting: A report, of the board of examiners on the iron steam battery constructing at Hoboken. January 6, 1862.— Referred to the Committee on Naval Affairs, and ordered to he printed. Navy Department, January 2, 1862.
From a congressional document of the 37th Congress, Second Session. HOUSE OF REPRESENTATIVES. Executive Document No. 23.
Removed from publication; thirteen pages. Full text is in notes. RTF doc on file.
The Stevens Battery was examined by a committee at the direction of Congress and the report here is highly critical.
See archives 2013.002.0001 for the text of a published newspaper article related to Stevens Battery.
HOUSE OF REPRESENTATIVES.
Ex. Doc. No. 23.
IRON STEAM BATTERY.
THE SECRETARY OF THE NAVY,
A report, of the board of examiners on the iron steam battery constructing at Hoboken.
January 6, 1862.— Referred to the Committee on Naval Affairs, and ordered to he printed.
Navy Department, January 2, 1862.
Sir: A joint resolution of Congress, approved July 24, 1861, having authorized the Secretary of the Navy "to appoint a board of examiners to examine the iron steam battery, now building at Hoboken, New Jersey, and ascertain what will be the cost of the same, how soon it can be completed, and the expediency thereof, and report thereon for the next meeting of' Congress," Commodores Silas H. Stringham and William Inman, Captain T. A. Dornin, Chief Engineer A. C. Stimers, and Joseph Henry, esq., were appointed a board for the purpose indicated. They have completed their duties and submitted a report, a copy of which I have the honor to transmit herewith for the information of Congress.
I am, very respectfully, your obedient servant,
Hon. G. A. Grow,
Speaker of the House of Representatives.
REPORT ON THE IRON STEAM BATTERY CONSTRUCTING AT HOBOKEN BY EDWIN A. STEVENS.
Navy Yard, Brooklyn, December 24, 1861.
Sir : In obedience to orders from the Navy Department appointing the undersigned members of a board to examine the iron steam battery, now building at Hoboken, New Jersey, and ascertain what will be the cost of completing the same, how soon it can be completed, and the expediency thereof, we met at this place on the 1st ultimo, and entered upon the above duties by examining so
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much of the battery as has already been constructed, and by desiring Mr. Stevens to furnish us with plans and descriptions of the vessel as she would be when completed, ready for service.
These latter were received on the 10th instant, previous to which the board had visited the battery frequently; and having carefully examined the vessel, as far as advanced, and the plans submitted for her completion, we beg leave respectfully to report, that we found upon the ground of Mr. Stevens, at Hobo-ken, situated in an excavation or dock, a long slender iron vessel, in an unfinished state, evidently intended for high speed in smooth water.
DESCRIPTION OF THE PORTION ALREADY BUILT.
The shell of the vessel is nearly completed up to a height of 31 feet from the bottom, but without the decks or the beams upon which they are to rest. This vessel is 420 feet long, by 45 feet extreme breadth. The iron plating, with the exception of a keel-plate, which is ten inches wide and one inch thick, and the garboard strakes, which are thirty inches and five-eighths of an inch thick, is half an inch thick, riveted to ribs of angle-iron, six inches deep, three inches wide, and one half-inch thick ; a similar angle-iron reversed being riveted to each rib. These ribs are spaced two feet apart throughout the entire length. Extending across the bottom of the vessel at each rib are floor timbers two feet deep, formed of plate iron one-half inch thick, along the lower edge of which is riveted the angle-iron ribs, and along the top edge of which is riveted the reversed angle-iron.
Upon fore and aft keelsons, made of plate iron in box form, 6 inches in depth and fastened to the tops of floor timbers, are placed ten horizontal fire-tube boilers, with the tubes over the furnaces. The boilers are arranged similarly to those in our large naval vessels, namely, five on each side, with one fire-room amidships, running fore and aft, common to both sides. These boilers occupy 80 feet of the length of the vessel, commencing at 124 feet from the stern. Within these boilers are thirty furnaces, with tubes of inches in diameter, and varying from 7 feet to 8h feet in length, placed over them. The shells of the boilers are one quarter of an inch thick, single riveted, with stays inch in diameter, placed 12 inches apart, attached to crow-feet, the toes of which are 6 inches apart; thus staying the flat surfaces every six inches. They contain, in the aggregate, 876 square feet of grate surface and 28,000 square feet of fire surface, as follows :
Tubes............................ 23, 380 square feet.
Furnaces......................... 2, 050 " "
Connexions.......................1, 890 " "
Tube sheets....................... 680 " "
Immediately abaft the boilers are the main engines, eight in number, already in a nearly completed state, occupying the whole breadth and depth of the present structure for a length of 53 feet. There are two propeller shafts, with four engines upon each, so arranged that each propeller is quite independent of the
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other. The engines are vertical, over-head beam, condensing engines, having common jet condensers, with vertical air-pumps, one condenser and air-pump serving for two engines. Each cylinder is 45 3/4 inches diameter by 3 1/2 feet stroke of piston.
The crank-shaft of each engine is forged separately with cranks, and crank pins forged on. These shafts are then connected together by a rigid coupling in such a manner that the entire shafting to each propeller, during a length of 186 feet, is rigid throughout. The brasses to these shafts are hollow, so that water may circulate through them, and keep the journals cool. The engines are provided with the ordinary slide valves, without cut-offs, worked by the ordinary Stephenson link, to cut off by lap at about half stroke. All the links upon each side are connected to a reversing gear, operated by a pair of reversing engines, very conveniently arranged, so that one man may readily manage, slow down, stop, start, or reverse the four engines attached to each propeller.
Forward of the boilers are two pumping engines and pumps for feeding the boilers; also two engines attached to each extremity of the same shaft, which extends across the ship, and upon which there is to be a large fan-blower, drawing its supply of air down through bomb-proof gratings in the bomb-proof deck above; causing throughout the lower part of the vessel an excess of pressure. This is to cause in the furnaces of the boilers a powerful draught independent of the height of the chimney, and throughout other parts thorough ventilation.
GIRDERS AND ENGINE FRAMES.
In rear of the boilers, attached to the sides of the ship, are strong plate-iron beams, running fore and aft, about 14 feet from the bottom. To these are attached five plate-iron girder frames, extending across the ship, and placed, one immediately forward of the forward boilers, and the other four between each pair of boilers. These fore and aft beams and athwart ship girder frames are very strong, and well calculated to strengthen that part of the hull, besides being capable of supporting any superincumbent weight that may be brought upon them amidships. The engine frames are eight in number, formed of plate iron, each extending quite across the vessel, and firmly fastened to the sides near the bottom, and at a height of about 14 feet above it. These engine frames are also well calculated to support any required superincumbent weight which it may be desirable to place upon them amidships.
WORK REMAINING TO BE DONE.
It now remains to complete a small portion of the plating near the bow and the stern; put in the beams and decks; attach a fore and aft box keelson to the floor timbers amidships throughout the whole length of the vessel; make the flue connexions and chimney to the boilers; connect the engines, and add a few wanting pieces; put in floor plates to engine and fire rooms; make and attach the propeller shaft bearers to the outside of the vessel; supply the propellers ; put in the required bulkheads ; apply the armor and the machinery for loading and working the guns; and to manufacture the guns themselves.
CHANGE OF PLANS.
Before describing the plans proposed for completing the vessel, it is proper to state that the original projector of the vessel was the late Robert L. Stevens, esq., deceased, and that his brother, Edwin A. Stevens, esq., who now proposes to complete it, has materially changed the plans from what appears to have been originally intended. Instead of the vertical sides above water, clothed with armor and pierced with gun ports, which seems to have been the design of Robert L. Stevens, the plans presented to us bear date of November, 1861, and
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resemble the inclined armor-plated ships, the designs of which have been patented in England by Captain A elderly Sleigh, in July, 1858, and by Mr. Josiah Jones in November, 1859, with the important exceptions that in the English plans the inclined armor is pierced with gun-ports, having an ordinary battery,, with the guns and gunners, protected overhead by a bomb-proof deck; whereas Mr. Stevens places his guns on the top of the upper deck, depending upon their immense size for their own protection, and for the protection of the gunner who aims and fires them, the training and loading of the guns to be accomplished by novel arrangements of steam machinery below the deck, yet to be elaborated the guns to be trained to a certain position and depressed twenty degrees, to bring the bore in the same strait line with that of a steam cylinder below, to the piston head of which is attached a rammer and sponge.
DESCRIPTION OF PLANS PROPOSED FOR HER COMPLETION.
The present plans of Mr. Stevens for completing the battery, of which the following description is derived from information, with illustrative drawings, furnished on call of the board, by him, contemplate an ordinary deck forward and abaft the machinery, 14 feet from the bottom, beneath which will be coal, fresh and salt water tanks, and powder magazine, and upon which will be salt water tanks, provisions, and shell rooms. At 21 feet from the bottom, a deck, which, forward and abaft the machinery, will be bomb-proof, by having a bottom layer of plate iron one-half inch thick; above this a layer of wooden planking, six inches thick, covered with another layer of iron one inch thick. This deck is continued over the machinery, but in this part is of ordinary material and strength.
THE ARMOR ABOVE WATER.
Over the latter part of the 21-feet deck is constructed, with inclined armor extending from 3 feet beyond the present side of the vessel to 14 feet inboard and 7 feet high, giving an upper deck, upon which the guns are to be placed, of 23 feet wide amidships. This inclined armor is formed of plate iron in seven laminae, six of which are one inch thick each, and the seventh three quarters of an inch, making the thickness of iron six and three quarters inches; supporting this iron armor are iron beams, eight inches deep, filled in between with locust; under these again are locust planks six inches thick, making, in all, six and three quarter inches of iron and fourteen inches of wood, placed at an angle of twenty-seven degrees with the horizon. The forward and after ends of what may be termed the loading-house within this inclined armor are enclosed by similar armor, inclined in a fore and aft direction, and it is forward and abaft of this that the 21-foot deck is bomb-proof.
The flat deck, uniting the upper edges of this inclined armor, is 120 feet long, and is made bomb-proof by having first a layer of plate iron one-half inch thick beneath the beams, between which is laid wooden planking six inches thick, which again receives two layers of iron of three quarters of an inch thickness each. Through this deck the heated gasses from the boilers rise between the bars of a bomb-proof grating, an ordinary smoke-pipe rising above the grating, which is to be removed, if desired, when going into action. Forward of the inclined armor, upon the 21-feet bomb-proof deck, are the capstans for weighing the anchors and the quarters for the men. Abaft the armor, upon the same deck, are the quarters for the officers, cabin, ward-room, and steerages. This bomb-proof deck and the inclined sides of the armor are covered with a light deck of 2-inch planking, supported by wooden beams 5 inches square and 2 feet apart, placed at such a height that its upper side is flush with the bomb-
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proof platform, upon which the guns rest. The edges of this light deck are supported by light iron sides one quarter of an inch thick, running up vertically from the outboard edge of the armor.
THE ARMOR BELOW WATER.
From the 21-foot line downwards 6 feet the sides of the vessel are protected by armor composed, first, of oak timbers placed next to the iron plating of the ship, having a thickness at its upper edge of 3 feet, with a triangular cross-section such that its outboard side forms a continuation of the slanting side of the vessel, which, up to the point of meeting the armor, has an angle with the perpendicular of about 26 degrees. From the 21-foot line down the outer side of this oaken armor extends, to a depth of 3 feet, iron plating 2 inches thick, within which, down to a depth of 2 feet, is iron plating one and a half inch thick, so that the side armor of the vessel, extending throughout the entire length, consists of iron 3 1/2 inches thick to a depth of 2 feet, and 2 inches thick for one foot further down, backed by solid oak 3 feet thick at the upper edge amidships, tlie thickness gradually lessening as it descends, until, at 6 feet depth, the iron side of the vessel itself is depended upon. As the vessel will draw 21 feet when loaded with stores, ammunition, and coal, the upper edge of this side armor will be on a level with the surface of the water. Near the bow and stern the oaken part of the side armor is not so thick as amidships, being 2 feet thick at its upper edge, at 40 feet from the bow and at 60 feet from the stern.
There are to be two short masts of hollow plate iron, arranged with hinges near the deck, similar to those in the English steamer Great Western, so that they may be lowered to the deck when going into action.
The armament proposed consists of five 15-inch Rodman guns, weighing, with their carriages, sixty thousand pounds each, and two 10-inch rifle guns, weighing, with their carriages, forty thousand pounds each. These, as before stated, are placed on the extreme upper deck, over the engines and boilers; the deck upon which they rest is supported by columns of wrought iron, which rest upon the engines' frames and the strong plate iron girders before described as rising from the bottom and sides of the ship, between the boilers. These guns are mounted upon carriages of a novel construction, so arranged that they may be trained to any point in the horizon, by simply revolving a vertical shaft which passes down through the deck and is attached to steam machinery below; the upper end of the shaft terminates in a T head or horizontal cross-bar, whose length is equal to the interior breadth of the gun carriage. Between this head or cross-bar and the interior ends of the carriage are India-rubber springs, 40 inches long, and when the gun is fired it is expected, from experiments which have been tried with a 10-inch gun of 10,000 pounds weight, and a charge of powder of 18 3/4 pounds, throwing solid shot weighing 124 pounds, and calculations deduced from them, that the gun will recoil, at a maximum, twenty inches, or one-half the length of the springs, and that the reaction of these springs will restore the gun to the position which it occupied before it was fired, similar springs upon the opposite side of the cross-bars receiving the shock caused by this reaction.
It is expected there will be one man on this upper deck in time of action to each gun, who will direct, by appropriate signals or indicators, its training to those below, and aim and fire it. It is considered by Mr. Stevens that guns of this size will not be injured even when struck by the enemy's shot. This, however, is to be the subject of experiment before the completion of the vessel,
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and if opposite result should be arrived at from these trials they are to be protected by wrought-iron armor, in a manner about which he has no doubt ; and that when the gunner sees a shot coming he can stand on the friendly side of the gun for his protection, the carriage underneath being made shot-proof by wrought iron armor plates. When the gun is to be loaded the gunner on deck causes it to be trained to the loading position, which in each case brings the gun nearly in line with the keel; he then depresses it about twenty degrees, bringing its muzzle opposite a bomb-proof opening in the deck, corresponding in size and direction to the bore of the gun. Below the deck is a long slender steam cylinder, having upon the outer and upper extremity of its piston-rod a compound sponge and rammer. The attendant admits steam to either side of this piston, as required, and sponges out the gun; then the ammunition, being placed in position near the muzzle, is rammed home by the steam rammer, after which it is elevated by the gunner above, trained upon the enemy and fired.
PROTECTION BY PARTIALLY SINKING.
When the vessel prepares for action with the enemy she is settled to a greater than ordinary draught by the admission of salt water, as follows:
Water to be admitted into tanks below 2-foot line............... 213 tons.
" "" " interstices of the coal................ 350 "
" " pumped up into tanks on deck.................... 537 "
Total water for settling.................................1,100 "
Only one-half of this water is required when the ship is down to her deep load line, but the whole amount is provided for, so she may be brought to the fighting draught when her coal and provisions are nearly out.
This settling of the vessel is for the purpose of adding to the armor plates the protection secured by water against shot.
TO BE LIGHTED WITH GAS.
The vessel is to be lighted with gas, generated on board, by placing the retort in one of the boiler furnaces, in a manner similar to that in use on board the ferry-boat Hoboken.
FLOATATION AND STABILITY.
To determine the flotation and stability of the ship, we have carefully computed the weights of the vessel and all that it is expected to be put in it, with their centre of gravity, the displacement of the vessel, the centre of gravity of displacement, and the height of the metacentre. The displacement of the side armor is included in computing that of the vessel, and the extra beam it gives the ship was considered in estimating the height of the metacentre. The weights include those of four hundred men and officers, provisions for three months, ten thousand gallons fresh water in tanks, one hundred and twenty rounds of shot and shells, one hundred and fifty rounds of powder, and eight hundred tons of coal.
The result of the calculations are as follows :
Draught of water 21 feet. Displacement in cubic feet............................. 188, 248
Displacement in tons of 35 cubic feet each................. 5,378.5 tons.
Add for iron plating...............................................................18.5 "
Total displacement ................................ 5,397.0 "
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Area of midship section.............................. 817.6 sq. ft.
Area of load water line..................................................................13,788.0 sq. ft.
Displacement per inch at load line................................................32.8 tons.
Weight of loaded ship by computation..................... 5,280 tons.
Add for contingent..................................... 117 "
Total weight provided for........................... 5,397
Depth of centre of gravity of loaded ship below load water line 5.49 feet.
Depth of centre of gravity of displacement below load water line 8.657 "
Height of metacentre above centre of gravity of displacement 10.535 "
Data for judging of the form of the vessel.
Midship section.Areas of immersed section.
Height from bot-Breadths.Distances fromAreas.
Having thus described the vessel and its appurtenances, it remains to state the cost, time required for its completion, and " the expediency thereof."
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The total cost of the vessel complete, except stores, is estimated
to be.............................................. $1, 283, 294 00
Of this amount there has already been paid by the government 500, 000 00
Leaving yet to be provided for...................... 783, 294 00
Of this latter sum Mr. Stevens states that he has expended,
from his own resources, towards the completion of the ship 228, 435 87
Leaving as a representative of the amount of work yet to
be done....................................... 554, 858 13
TIME REQUIRED FOR COMPLETION.
The time required for completing the entire structure, ready for service, is estimated by Mr. Stevens at four months from the date of recommencing the work.
EXPEDIENCY OF COMPLETING HER.
The expediency of incurring the above expense in producing such a vessel as described is best determined by examining in detail the many novel characteristics which she would possess.
She differs from the ordinary war vessels with which we are acquainted,
1.In having long slender ends.
2.In employing two independent propellers, with several engines attached to each.
3.In depending entirely upon a fan-blower for the ventilation of the lower part of the vessel when in action.
4.In employing a heavier armament than has ever yet been put afloat; and training and loading these heavy guns by steam machinery, below the deck, manipulated by persons who do not see the guns.
5.In having the guns exposed to the direct fire of the enemy, upon the top of, instead of within, an iron-clad vessel.
6.In settling the vessel when going into action; and in several other respects which will develop themselves in the course of this report.
1st. The great length of this vessel, compared with her transverse strength, strikes a nautical man at once, and a careful investigation clearly indicates that it would be the height of professional imprudence to send such a vessel to sea. The action of the waves would cause her to writhe and twist to an extent that would soon open the seams of her light iron sides. Her use, if completed, would therefore be confined to the defence of the harbor. Here her inconvenient length and her draft of water, which could not be reduced to much less than 19 feet, even for this service, when fully equipped, would militate against her usefulness to a certain extent.
2d. The employment of two independent propellers instead of one would appear to possess great advantages in effecting great rapidity of manoeuvre when in presence of the enemy, and would be all the more useful to her from being compelled to confine her operations to the defence of the harbor, the channels of which would be rendered comparatively restricted by her great length and draft of water.
The application of more than two engines to one propeller-shaft, arranged, as in the case of this vessel, to occupy a considerable portion of the length, has its advantages and disadvantages. It no doubt distributes over a greater area the reactive strains which the engines bring upon the vessel when they are in opera-
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tion, but it also adds to the first cost of the machinery, the space occupied, and the labor of attendance.
3d. In ventilating the lower part of the vessel by artificial means during action, it must not be forgotten that fresh air is a constant necessity to human life, and to maintain it in this vessel there must be always steam up, and the fan in operation.
4th. One of the most important features of the vessel is that of using very heavy guns. The five 15-inch smooth bore and the two 10-inch rifle guns throw fifty per cent, greater weight of metal per broadside than our heaviest 44-gun steam frigates armed with heavy Dahlgren guns.
5th. It being a part of the design of this vessel that these guns shall be large enough for their own protection against the shot of the enemy, it would be well to examine the question of how large must be the mass of cast iron to secure it against injury from such a source. The 15-inch Rodman gun now at Fortress Monroe is four feet diameter at the breech, and two feet one inch at the muzzle; is fifteen feet ten inches long, and weighs 49,100 pounds.
Experiments were tried at Woolwich, in England, in September, 1857, by firing from a sixty-eight-pounder, ninety-five hundred-weight gun, with a charge of 16 pounds of powder, four wrought-iron shot, at a distance of 600 yards, and cast-iron shot, at a distance of 400 yards, at a target composed of three cast-iron blocks, each eight feet long, 2 feet high, and 2 1/2 feet thick — average weight of each block, 8 tons. They were placed one above another, a groove being cast oil the upper surface of the upper block 3 inches deep by 14 inches wide, to receive a corresponding projection on the under surface of the block above it.
This target was supported in rear by a rectangular mass, consisting of six heavy blocks of granite, each block 4 1/2 by 3 by 2 feet, leaving 4 1/2 feet of the centre of the target unsupported. This wall of cast iron was struck ten times, and entirely destroyed.—( Vide Naval Gunnery, by General Sir Howard Douglass, 5th edition, pp. 404, 405.)
There is no doubt in our minds but that the metal of the Rodman gun is much stronger than that of the cast-iron blocks forming the target above described, (for reasons of which see Notes on Sea-coast Defences, by Major Barnard, U. S. A., p. 36,) but still the results are so remarkable that, until further experiments are tried, bearing more immediately upon the case, we cannot consider any cast-iron gun as proof against the assaults of heavy ordnance, when exposed, as these are, to the direct aim of the enemy, by being placed upon the extreme upper deck of the vessel, with neither bulwarks or railing to screen them from view, and with the necessity of being trained to a position nearly in line with the keel every time they are loaded. Mr. Stevens has stated to the board that, if experiment shall establish that the guns are not thus, in themselves, their own protection from the effects of shot, he is prepared to cloth them with angular wrought-iron armor, which he considers will certainly be effectual.
6th. The project of settling the vessel down two feet beyond her deep load draught, when preparing her for action, by admitting water from the sea to different compartments of the vessel, and, after the battle is over, elevating her again to the normal draught by pumping the water out, is so remarkable a departure from all previous naval practice that the board have given the subject considerable attention in its various bearings upon practical operations.
Firstly. With regard to the compartments within the vessel which are to receive the water. The statement of Mr. Stevens upon this point is, that 213 tons are to be admitted into tanks below two-feet line. Now, these tanks are neither more nor less than the spaces between the floor timbers of the ship, or, in other words, the bilge, a part of the vessel which every prudent commander keeps as free from water as possible; but, aside from this, it is well known that the bilge water, of steamers especially, is constantly liable to choke the pumps, on account of the debris contained in it, so much so, that in all good steamships several dif-
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ferent pumps are arranged to pump from the bilge, not so much with, the expectation that they will all be required at once as that some of them may always certainly be in good pumping order.
The statement of Mr. Stevens further is, that 350 tons are to be put into the interstices of the coal. This we regard as highly impracticable. To say nothing of the impossibility of getting coal from the bunkers while they are full of water, the difficulty of again pumping the water out, filled as it would be with small particles and dust of tire coal, entirely precludes, in our opinion, the use of that part of the ship for such a purpose. Mr. Stevens proposes to use a kind of pump for this purpose which it would appear has worked very well for similar purposes in civil engineering. Its application to vessels-of-war, however, is novel, and it is liable therefore to the objection of all untried projects.
Secondly. The quarters for the men and officers are upon the bomb-proof deck, which is about on a level with the surface of the water at the ordinary deep-load draught, and would therefore be two feet below it when the vessel was in action. Her sides above this deck are made of thin iron, easily perforated by the lightest artillery; so that a heavy shot forward or abaft the loading-house, making a large perforation near the water-line, would flood this entire deck, adding immediately an enormous weight to the vessel, for which no provision had been made. But one consequence could follow such a disaster — the ship would sink. From these considerations it is very clear to us that, whatever theoretical excellence there may be in sinking the vessel for her better protection in time of action with an enemy, the plans here proposed for putting the project into execution are entirely impracticable, and would never be resorted to by any prudent commander.
HULL NOT SUFFICIENTLY STRONG TO SUPPORT ARMOR.
The sides of the vessel above the fourteen-feet line have no extra supports beyond those usually applied to a merchant steamer, and yet, in the proposed plans, they are to sustain the weight of the side armor and the upright side which rises from its upper edge, which amounts to 350 tons. Added to this is one-half of the upper inclined armor which protects the sides of the loading-house under the guns, amounting to 450 tons, making together 800 tons to be carried by the upper edges of these light, overhanging sides, without any provision being made to carry any extra weight whatever. This strikes us as a remarkable defect, which it would be difficult to remedy in any manner, even if the buoyancy was sufficient to carry the added weight of such remedies.
EFFIENCY OF THE ARMOR.
Aside from the above defect, there can be little doubt that the loading-house is efficiently protected against the heaviest ordnance now afloat in any part of the world. Above water the armor is fifty per cent, thicker than is applied to the French and English iron-clad vessels, and, instead of being placed at right angles to the line of direct fire, is at an acute angle with it, an immense advantage in attaining impregnability.
The side armor, where it joins this upper loading-house portion, is well calculated to protect the vessel if she be kept at all times down to the loaded draught ; but forward of this, during a length of 96 feet, and abaft for a length of 136 feet, we regard it as very deficient in having the iron plating placed in an inclined position, while the oaken backing only supports it horizontally. Although the shot comes in a horizontal direction, the pressure upon the plating is at right angles to its surface, and therefore partially upwards. The result would be that the iron would give way for want of proper support in the direction where the support was needed.
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This would not admit the first shot which strikes this armor to the interior of the vessel below the bomb-proof deck, but there would be very little protection against the next shot which struck near the same place.
POWER AND SPEED OF THE VESSEL.
In designing the form of the vessel and determining the amount of steam power which should be placed in her, great sacrifices have been made to attain the very important desideratum in a war-steamer, high speed.
It is claimed by Mr. Stevens that her machinery is capable of exerting a power of 8,600 horses, and that this will give her a speed of twenty sea miles per hour—greater, it is believed, than that of any war steamer in the world. Although, for reasons already stated, the sphere of action of the vessel would necessarily be confined to the defence of the harbor, where great speed for any distance would not be required, but where, nevertheless, a high speed, even for a short distance, might, when manoeuvring against an enemy, be of immense advantage. Indeed, the great power claimed would be of very great advantage simply when applied to the propellers in opposite directions, for the purpose of turning round quickly.
To obtain this power of 8,600 horses, it is proposed to carry within the boilers a pressure of fifty pounds per square inch, and to run the engines seventy-five revolutions per minute.
With the above pressure and revolutions given, the power would be obtained, but prudent engineers would not place the limit of maximum pressure to be at any time carried upon boilers of this description at higher than twenty-five pounds per square inch. Not the slightest objection is urged against the use of steam of as high a pressure as fifty pounds per square inch, however, even when, as in this case, salt water is to be used in the boilers, because, as far as the latter condition could be brought as an objection, it is replied that such a pressure and the resulting power would only be required for a short time, at probably great intervals ; but if high pressure be desired, boilers strong enough to carry it with perfect safety should always be provided.
With regard to running these engines at a speed of seventy-five revolutions per minute : It will be remembered that each system of crank shafts has eight bearings, or one at each engine-frame, and that although the part which receives the power of each engine has been forged separately from the others, they are coupled rigidly together, giving what is virtually a single rigid crank-shaft of fifty-three feet length, with eight bearings. Each of these bearings is so arranged that it may be turned as on a pivot both in a horizontal and vertical direction, which would be a very useful quality if there were but two bearings, as then the axis of each could always point towards the other, no matter in what direction the cramping of the ship would move them; but it is clear that, when there are more than two, each bearing must remain in a fixed position or their axes will not be in the same straight line, but these bearings, extended over so great a length of the vessel, would, when the full power of the engine is upon them, depart materially from the straight line which perhaps existed when in a state of rest; and the result would be that, the journals of the shaft would be cramped in their bearings to an extent that would cause them to heat beyond the power of water to keep them cool, when running at higher speed than forty revolutions per minute.
There would be little or no difficulty, however, in overcoming this defect by substituting movable for rigid couplings between the crank shafts of each separate engine. With this modification there would be no difficulty, as far as the machinery was concerned, in running them eighty revolutions per minute. The power of 8,600 horses would therefore be modified as follows:
[page] 12 IRON STEAM BATTERY.
The mean effective pressure per square inch upon the piston when carrying fifty pounds of steam in the boilers was fifty pounds, in the calculations of Mr. Stevens. When carrying twenty-five pounds in the boilers this would be twenty-nine pounds, which would therefore give 8,600 X 80 by 29, 75 by 50, X 5,320 horse-power. Even this allowance gives the boilers credit for the excellent performance of producing one horse-power for every five and a quarter square feet of fire surface.
If, therefore, 8,600 liorse-power would produce a speed of twenty miles an
hour, that of 5,320 horses would give 3 [square root] 20 3 X 5320 over 8600 seventeen miles, nearly.
With regard to having allowed in this modification of the power an increased number of revolutions with a lessened pressure, it may be proper to state that the propellers have not yet been designed, and it will only be necessary to give a less pitch to them than would have been required with the greater pressure.
INABILITY TO FIRE IN A LINE WITH THE KEEL.
One of the important features claimed for this vessel is that each of her guns may sweep the horizon without changing the direction of the ship : that she could advance upon the foe with her unrivalled speed, firing her enormous guns in a direct line with her keel as she approached; similarly, that if chased by superior force she could retire rapidly, at the same time that nearly her whole armament was sending back its destructive shot and shells.
The armament, considered by itself, is certainly as well arranged for firing several guns in a line with the keel as in any other direction; but it will be remembered that forward of the guns, forming the quarters for the men, and abaft them, forming quarters for the officers, is a light wooden deck, made of two-inch planking, supported by wooden beams five inches square, placed two feet apart. Every artillerist knows what would become of this deck upon firing the first 410-pound shell across it a distance of one hundred and twenty feet: it would be demolished; and so also would be the same deck where it extends over the inclined armor when the guns were fired en broadside; but here it would not be of so much importance: the deck, and the light sides which support it, could be dispensed with, and might well be left out in the construction of the vessel; but the deck forward and abaft is a necessity, and would be destroyed by any prudent commander only when driven to the last resort. She would be compelled, therefore, to lay her broadside to the enemy, exposing to his fire the full length of each gun every time it was placed in position for loading.
In conclusion, we beg leave to express our highest appreciation of the objects Mr. Stevens has apparently had in view when planning this vessel — the most powerful battery, the highest speed, and the most thorough protection of any vessel yet produced — and our regret that the plans of the vessel, as presented to us, would not, in our opinion, accomplish fully and completely the ends proposed.
We look with the deepest interest upon every addition to the efficiency of our navy, of whatever character; gladly hail every improvement made to any department of it; but at the same time we cannot recommend the expenditure of important sums of money upon projects of more than doubtful success when put
[page] 13 IRON STEAM BATTERY.
into practical execution; and therefore we do not deem it expedient to complete this vessel upon the plans proposed.
All of which is submitted by, very respectfully, your obedient servants,
President of Board,
THOS. A. DORNIN,
Captain United States Navy.
ALBAN C. STIMERS,
Chief Engineer United States Navy.
Hon. Gideon Welles,
Secretary of the Navy, Washington., D. C.
I readily concur with the other members of the board of commissioners in the statement given in the foregoing report as to the condition of the vessel as it now is, and in reference to the general account of the plan proposed by Mr. Stevens for furnishing it, as well as in the statement given as to the amount of money and length of time which would be required to complete the vessel in accordance with the plan proposed. I also highly appreciate the objects intended by Mr. Stevens and the laudable endeavors which he has exhibited to improve the defences of our harbors; but I cannot, with my present knowledge, concur in the decided opinion expressed by the other members of the board in regard to the inexpediency of finishing the vessel.
If I rightly understand the design of Mr. Stevens, it is not to confine the operations of the battery to inner harbors, but also to employ it in outer harbors, and especially in the waters immediately beyond; and therefore the important problem to be solved is whether the vessel can be so finished, in conformity with the general plan proposed, as to withstand the waves of the sea to which she may thus be subjected. All the material objections which have been brought against the plans of Mr. Stevens are, in my opinion, merged in this one question ; and from a due consideration of all the facts which have thus far been presented to me, I am not convinced that it cannot be solved. On the contrary, it appears to me that, although the vessel may not be a convenient or safe ship for long voyages, she might be made of sufficient strength to withstand the exposure to which she would be subjected, and to efficiently perform the service required. If requested to do so, I will furnish the reasons for this opinion at a future time.
|Year Range from||1861|
|Year Range to||1862|
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