Before entering upon the description of the cruisers just laid down for the Navy, it may be interesting to recall briefly the events which led to their production.
In June, 1881, the Hon. William H. Hunt, Secretary of the Navy, recognizing “the pressing need of appropriate vessels in the service,” appointed an Advisory Board, consisting of fifteen officers, selected with care from the constructing and executive corps of the Navy, and presided over by the late Rear-Admiral John Rodgers.
Four months' time was allotted to the Board to consider and report upon the number of vessels which should now be built, their class and size, material and form of construction, nature and size of machinery for each, ordnance and armament, appropriate equipment and internal arrangements. This would have been a tremendous undertaking for a body of experts accustomed to working in concert, but doubly difficult for such a Board. The report, which was incorporated by the Secretary in his annual report to Congress, passed over the subject of ironclads as not a present necessity and requiring more careful consideration and more intimate knowledge of modern practice than time would permit them to enter into or acquire. The necessity of reconstructing the cruising fleet was forcibly presented, and the general opinion of the Navy and the country well represented by the recommendation that thirty-eight unarmored cruisers of different classes should be built, which would have provided at the end of eight years a peace navy of seventy cruisers, of which about twenty would have been fair commerce-destroyers in time of war. The war navy was for defense only, and was to consist of five rams, five torpedo-gunboats, and twenty fast torpedo-boats.
The details of the report formed a rich field for criticism, both as to fact and opinion, and was the subject of much discussion in the press and in naval circles during the following session of Congress. The Naval Committee, led by the Hon. W. B. Harris, of Massachusetts, sifted the matter carefully, interrogated the members of the Board individually, and examined the shipbuilders and steel-makers of the country and many naval officers. In March, 1882, the committee reported to Congress, setting forth more clearly even than had been their custom for the preceding six years, the humiliating condition of the Navy, and recommended that six of the larger cruisers, one ram, and eight torpedo-boats be built. The bill presented therewith unfortunately contained measures making radical changes in the personnel and administration of the Navy, which prevented it from obtaining a hearing. Finally, owing to a political difference between two committees of the House, no appropriation was made for the increase of the Navy; but the Navy bill authorized the construction of one each of the two larger classes of cruisers recommended by the late Advisory Board, from any unexpended balance of the appropriation for the Bureau of Construction and Repair. This act created the present Naval Advisory Board, consisting of five officers of the Navy and two civilian experts. It requires the Board to advise and assist the Secretary of the Navy in all matters referred to them relative to the designs, plans, etc., of the vessels authorized to be built, makes the approval of the Board necessary for all such plans before work can be commenced, and gives the Board general supervision of the construction and trial when complete, under direction of the Secretary of the Navy. This Board was organized in November, 1882, with Rear-Admiral R. W. Shufeldt as President.
Congress, at the last session, upon the recommendation of this Board and the Secretary of the Navy, reauthorized the construction of the smaller of the two cruisers provided for in the act of 1882, and in addition two cruisers of about 3000 tons displacement, and one dispatch-boat, and appropriated $1,300,000 to commence their construction and procure the armament. Under the direction of the Secretary of the Navy, the Naval Advisory Board prepared general designs and published circulars giving the general features of the design of each vessel. These were submitted to prominent shipbuilders for suggestions, and upon their approval by the Department, the details were prepared in the appropriate bureaus, subject to the examination and approval of the Board. The Secretary of the Navy having decided to utilize the national navy-yards only for the construction of the masts, spars, rigging, boats, stores, etc., and ordnance, advertised on May 2d, 1883, for proposals for the construction of the four vessels. Sixteen bids were received for the vessels separately, from eight different firms. Those of Mr. John Roach, of Chester, Penn., proved the lowest in each case, his total bid being $2,440,000; $774,000 less than the Board's estimates, and $315,000 less than the next lowest bidder. These great variations were due to the lack of definite knowledge of the price of the high grade of mild steel required by statute.
About the 1st of August, the detail plans of the hulls and machinery having been approved by the Board and the Department, contracts were entered into with Mr. Roach for the following vessels, viz.:
Twin Screw Steam Cruiser Chicago.
Length between perpendiculars, 315 ft.
Length on water line, 325 ft.
Length over all, 334 ft. 4 in.
Depth from garboard strake to under side of spar deck, 34 ft. 9 in.
Height of gun deck port sill from load water line, 10 ft.
Height of spar deck port sill from load water line, 18 ft. 6 in.
Breadth, extreme, 48 ft. 2 ½ in.
Draught of water at load line, mean, 19 ft.
Displacement, 4500 tons
Area of plain sail, 14,880 sq. ft.
Complement of men, 300
Battery, four 8-inch long breechloaders in half turrets, eight 6-inch and two 5-inch on gun deck
Indicated horse power, 5000
Sea speed, 14 knots
Capacity of coal bunkers, 940 tons
Contract price for hull, machinery and fittings, exclusive of mast, spars, rigging, sails, &c., $889,000.
The Chicago is a coal-protected steam cruiser, built of mild steel throughout and without wood sheathing, and will contain the latest improvements in naval construction and ordnance. The battery will consist of four 8-inch high-powered breechloaders, weighing about 12 tons each, mounted in projecting half-turrets on the flush spar deck, the centre of the trunnions being 20.25 ft. above water. The turrets are unarmored, and the guns fight in large open ports. The only protection for the men is afforded by shields on the guns. The train of the forward guns will be 3° across the bow to 60° abaft the beam, and similar aft. Six 6-inch B. L. R., weighing about 4 tons each, will be mounted in broadside on the gun deck, with a train of 60° before and abaft the beam. This deck has been arranged and ports will be cut for two additional 6-in. guns on each broadside, which may be fitted if found desirable at any time. One 6-inch will be mounted in a recessed gun-deck port on each bow, with a train of from 3° across the bow to 52° abaft the beam. Two 5 -inch guns in recessed ports abaft the captain's cabin complete the main battery. The weight of the 8-inch projectile is 250 lbs.; 6-inch, 100 lbs.; 5 -inch, 60 lbs. There will be in addition, four 47 mm. and two 37 mm. Hotchkiss revolving cannon, mounted in fixed bullet-proof towers. Considering that these guns fire from 60 to 80 rounds per minute, and the shot from the heavier calibre can pierce the side of any unarmored vessel at 2000 yards, we obtain a conception of what a formidable element they will form in warfare. The number of probable hits from such a machine-gun battery along the water line emphasizes the great importance of minute watertight subdivision, both horizontal and vertical.
The Chicago is divided by nine complete transverse bulkheads extending to the gun deck, into ten main watertight compartments. The four amidship compartments, extending over 136 feet in length, are occupied by the machinery and boilers. An inner bottom extends throughout this space, forming a double bottom 3 ft. 6 in. deep amidships, which is divided by the vertical keel and transverse watertight frames into fourteen watertight cells.
The machinery and boilers are covered by a protective steel deck 1 ½ in. in thickness. The top of this deck is one foot above the load water line and is nearly flat, or has the ordinary round of the beams for about half the breadth amidships. At about 12- ft. from the side it bends downwards, striking the side at 4 ft. below the water line. Vertical longitudinal bulkheads extend on each side of and throughout the length of the machinery and boiler compartments. The space between them and the sides of the ship will be filled with coal, giving a coal armor of 9 ft. in thickness from the water line to 8 ft. above it, and aft an average thickness of 5 ft. from the water line to 14 ft. below it. These coal bunkers, with the pockets in the boiler rooms, form thirty -four watertight compartments when the doors are shut. The machinery compartments contain the vitals of the ship, and demand all available protection. It is not expected that the deck which covers them will resist a 6-inch shot at even so small inclinations as 6° to 8°, but the protection afforded by such a deck is of great value in preventing the direct access of shot and water to the main compartments, in resisting machine gun-fire, and from the fact that entering shell will probably explode among the coal without injury to the machinery.
The magazines, shell rooms and fixed ammunition rooms are situated in the hold amidships, directly before and abaft the machinery space, only separated from the forward boiler room by the cable tanks, and from the after engine-room by a handing and light room. The flats beneath them are watertight and form a virtual double bottom extending about 40 feet before and abaft that properly so called. The deck above them is covered by protecting plating ¼ in. thick, the remainder of this deck is of steel 1 in. thick, making a complete watertight flat. All hatches leading through it have watertight covers, and the magazine hatches are surrounded by coffer dams leading to the berth deck. Additional bulkheads of steel make other necessary divisions in the hold, and with the shaft alley bulkheads and those already mentioned divide the ship into 85 watertight compartments.
A complete system of drainage is provided for by which the total pumping power of the steam and circulating pumps, with capacity of 2500 tons per hour, can be concentrated on any main compartment. In addition to the steam pumping system, there are six continuous acting hand pumps on the berth deck which have independent suctions to each main compartment and each compartment of the double bottom; they deliver into the fire main or directly overboard as required, and can also be used for flooding any compartment or flushing the large drain pipes. A fire main extends about three-fourths of the length of the vessel amidships on the berth deck with stand pipes to gun and spar decks, and will have cocks with hose attached at intervals on each deck; this main is supplied by one of the large steam pumps or any or all the hand pumps.
Material and Scantlings.—The Act of Congress of August 5, 1882, required these vessels to be “constructed of steel, of domestic manufacture, having as near as may be a tensile strength of not less than 60,000 lbs. to the square inch, and a ductility in eight inches of not less than 25 per centum.” See Appendix I. for “Tests of Steel for Cruisers.” The outside plating will weigh 23 lbs. per square foot, or be about 9/10 in. in thickness; worked lap jointed, and double riveted at edges and butts to the height of the protective deck, and flush jointed, for appearance sake, from there up, the flush jointed plates being single riveted at the edges. The sheer strake will be doubled for about 250 feet amidships, and a doubling plate will be worked at the water line extending from the stem to about 70 feet from the stern. The flat keel is formed of two thicknesses of plate each 25 lbs. per square foot, the vertical keel of plate 20 lbs. per square foot, or 2 in. thick; the continuous angles at its upper edge will be 3” X 3” X 7 lbs. per lineal foot, those at the lower edge 3” X 3” X 81 lbs. The butts of the vertical keel will be double strapped and treble chain riveted. Each butt of the flat keel plates will have a butt strap of the same thickness as the plates and treble chain riveted. The stem and stern post will be of hammered steel. The watertight inner bottom will be of plating 12 ½ and 10 lbs. per foot, except the shoveling flat in the wing coal bunkers, which will be 15 lbs, or ¾ in. thick.
The transverse frames formed as shown in plate II, are spaced four feet apart throughout the double bottom, and three and a half feet elsewhere. The framing throughout the double bottom is on the bracket plate system, the frames being each 5” X 3” X 10 lbs., and the brackets 12 ½ lbs. per square foot. The outer frame angle is continuous from keel to armor deck, and the reverse frame is continuous from the second longitudinal to the same height. Above the protective deck both frames continue to the spar deck. Before and abaft the double bottom the frames will be of the ordinary construction, the outer being continuous from keel to upper deck, and the inner bar from the second longitudinal up. This framing is continued to the extremities, the run having been kept sufficiently full to obtain the strength necessary to carry a protected rudder. The longitudinal frames within the double bottom are formed of continuous plates 3/8 in. thick, slotted over the outer frame angle; the inner continuous angles being 2 ½” X 2 ½” X 5 lbs. per foot, and the outer intercostal bar 3” X 3” X 7 lbs. The third longitudinal from the keel will form the outer boundary of the double bottom, and will be composed of intercostal plates of 15 lbs. per square foot and stapled angles 2 ½” X 2 ½” of 5 lbs. This is made carefully watertight. The fourth longitudinal from the keel stiffens the framing in the wing coal bunkers, and is continued right fore and aft. The longitudinal is also continued fore and aft as the berth deck stringer.
The main bulkheads are formed of plate 121 and 10 lbs. per square foot, stiffened by vertical angles 3” X 3” X 7 lbs. each, 30 in. apart. Below the berth deck horizontal T bars will be fitted, possessing additional stiffness and serving as edge strips. It is well to notice here that as the bulkheads and inner bottom are comparatively light—mainly ¼ in. and 5/16 in.—the durability of these parts will mainly depend upon the care exercised by commanding officers in keeping the ship dry, clean, and well painted. With this view, great pains will be taken to make every part accessible.
Spar Deck.—Stringers 11 ft. wide amidships of 17 ½ lbs. per square foot, flush jointed, single riveted at the edges, and double at the butts. Tie plates at side of hatches.
Gun Deck.—Stringers 14 ft. wide amidships, covering the side coal bunkers, of 122 lbs. per square foot. Continuous ties at sides of hatches. The plating on both these decks will be reduced to 10 lbs. per square foot at the extremities.
Berth Deck.—Protective plating for 136 ft. amidships over the engines and boilers. This will be worked in two thicknesses of ¾ in. each, forming butt straps and edge strips for each other. Before and abaft protective plating there will be a stringer 36 in. wide and 15 lbs. per square foot. Watertight flats before and abaft machinery spaces, plating 10 lbs. per square foot.
It will be noticed, from the arrangement of deck plating and the comparatively heavy bottom plating, that the Chicago will have ample structural strength. In fact, it has been estimated that under the most unfavorable circumstances of the vessel resting on the crest of a wave and subjecting to hogging, that the stress on the upper deck plating will not exceed three tons per square inch.
The rudder and steering gear are completely beneath the water line. Additional protection is given to the rudder-head, false rudder-post and tiller, by a horizontal shield or flat 1 ½ in. in thickness. A fighting hand wheel and the steam steering engine will be situated on the watertight flat, to which communication can be made by telegraph from the bridges. There will also be a hand-steering wheel aft on the spar deck, and a steam-steering wheel in the pilot-house on the forward bridge. There will be two bridges, one forward of the smoke-pipes, extending over the 8 -inch gun turrets. On this bridge a roomy chart-house and, probably, an armored pilot-tower will be placed. The second bridge will be over the after half turrets.
The Chicago will be bark-rigged—the area of plain sail being 14,880 square feet, or about two-thirds full sail-power. It is intended that sail shall be auxiliary, as the coal supply is ample to supply power for long voyages under steam alone. The normal coal supply is 800 tons, the bunker capacity is 940 tons, and 300 tons additional can be safely and easily stowed on the berth deck. Thus, with a total coal supply of about 1240 tons, the Chicago can steam 3000 miles at 15 knots and 6000 miles at 10- 11 knots per hour.
Passing to the structure again, the bow of the vessel will be strengthened for ramming; the peak compartment being carefully subdivided by an additional bulkhead, watertight flats and breast hooks, in order to insure, as far as possible, that damage incurred in ramming shall not extend beyond the collision bulkhead.
The vessel will be ventilated by an exhaust system similar to that so successfully employed on the U.S.S. Richmond. Two large blowers situated on the berth deck draw air through large ducts extending fore and aft and with branches to all living spaces and storerooms, and deliver into ducts leading to the open air. A separate system is used for the engine and boiler compartments. Pipes are fitted leading from the topsides to supply fresh air to the coal bunkers, and another system, delivering into the funnel casing, provides an exhaust for gases which may escape from the semi-bituminous coal to be carried.
Machinery,—The Chicago will have twin screws, actuated by two pairs of two-cylinder compound overhead beam engines, shown in plate V. Each engine, with its independent auxiliary machinery, will be placed in a separate watertight compartment 22 feet long and enclosed by the protective deck, which is 12 inches above the water line amidships, giving a height in clear between the inner bottom and the under side of beams of 15 feet 8 inches.
The high and low-pressure cylinders will be located side by side, with axes vertical, eight feet apart and respectively2 feet 1 inch and 3 feet 5 inches from the midship line, the cylinders of the forward engine being placed on the port side. Their diameters will be 45 and 78 inches and their piston stroke 52 inches. Each cylinder will be steam-jacketed and fitted with two double-ported main slide valves, worked by means of eccentrics through arms and rock shafts, each fitted with a steam cylinder and piston to balance the weight of the valves. Cut-off valves receiving motion from the beam centres, and adjustable between the limits of 1/8 and 5/8 of the stroke, will be fitted to the back of each main valve. The exhaust steam from the high-pressure cylinder will pass directly to the low-pressure steam-chests; it will also be arranged with suitable pipes to exhaust the steam into the condenser and atmosphere. The low-pressure cylinders will be fitted to receive the steam directly from the boilers, and also to exhaust into the atmosphere. The condensers are to be placed outboard of the low-pressure cylinders and to rest upon them and the frames of the air and circulating pumps. They will have tinned brass tubes exposing a cooling surface of about 5000 square feet each. An independent, double-acting, combined air and circulating pump will be placed beside each condenser. Two double acting feed pumps five inches in diameter will be worked from the cross-head on the piston of each pump.
The crank shafts for each engine will be “built up” steel forgings in two separate interchangeable sections, and secured to each other and the line shafting by couplings forged on the shafts. The line shaftings will be of steel 13 in., the after section being 13 ½ in. in diameter. The outboard portion of the shaft will be supported by two hangers or A frames. The propellers will be made of steel with four adjustable blades, to have a diameter of 15 ft. 6 in., and a mean pitch of 22 ft. 6 in. The beams are to be constructed of two cast steel plates of parabolic form, about 11 feet long between extreme centres; greatest depth of beam 48 in.; the web of the plates will be 1 ½ in. thick, with a perimeter 3 in. wide and 2 in. thick; the bosses for the beam centres to be 20 in. in diameter and 12 in. thick, those for the connecting rods to be 15 in. in diameter and 7 in. thick. These beams may be constructed of rolled steel plates. All the pins will be of steel. The beam pillow blocks and the fram.es upon which they rest will be constructed of cast steel, the body of the frames to be 16 in. wide and 1 ½ in. thick, the side flanges 18 in. wide and 1 ½ in. thick; one foot of each frame rests on and is firmly bolted to the crank shaft block, while the other rests on the steam-chest.
The reversing cylinders will be located between the cylinders and crank shafts, and will connect directly with the arms of the rock shafts; the valves to be operated by floating levers from the working platform. This platform is outboard of the crank shaft and opposite the space between the cylinders.
Beam engines have long been successfully employed in paddle steamers, but only occasionally used for screw vessels. One well-known instance, however, is the Louisiana, the fastest vessel on the regular lines from New York to New Orleans. Their application to the propulsion of a twin screw protected cruiser is novel, if not unique; but their adoption is not in the nature of an experiment, and was only after careful comparison with special designs of both vertical direct acting and horizontal types. It was found impossible to get a vertical inverted cylinder engine beneath the water line, and, if used, it would certainly have exposed the vessel to vital injury from guns of small calibre. On comparison with horizontal engines, the advantage of vertical cylinders in wear and less work lost in friction, the longer stroke and connecting-rod, the easy accessibility of the working parts of the beam engine, led to its adoption. We generally find poppet valves employed on beam engines, and it has been proposed to use them on the Chicago. Their advantages of small power required to work them and definite action are undoubted; but it has been the general opinion that their success would be doubtful when used upon an engine of this size, making as many as eighty turns a minute.
In regard to the use of twin screws, it seems hardly necessary to repeat the lines of argument concerning them. There seems to be little doubt they are equally if not more efficient as propellers than single screws. A war vessel now building of over 3000 tons displacement, with single screws, is an exception, on account of the great advantage of subdivision of the power; for, if one engine is broken down, three-fourths speed can be maintained with the other. This arrangement admits of more complete watertight subdivision and more convenient stowage—the engines for each screw being entirely independent and in separate compartments, the motive power cannot be disabled by bilging a single compartment. Again, experienced engineers do not consider it safe to put the tremendous powers now used into a single engine unless they are subject to periodical and frequent overhauling, as in the case of merchant steamers. The merchant service does not use twin screws on account of their greater first cost, larger running expenses, the liability to injury alongside docks and greater space occupied; all of which are good commercial, but not good military or scientific, reasons against their employment. It is found from experience that twin screw engines do not weigh much more than single engines of the same power. Twin screws render it possible to place the rudder and steering gear beneath the water line, and also furnish additional maneuvering power. With one screw going ahead and the other astern, a vessel can turn nearly on her own centre, though the time is slightly greater than when turning under full headway. This economy of space is, however, a great tactical advantage.
The weight of the machinery forming such an important factor in the design, the question of coal has demanded attention. It has been the custom to put into our naval vessels about fifty per cent, more grate surface for corresponding power than is customary in any national or merchant marine, the object being to use anthracite instead of soft coal, their rates of combustion being in the ratio of 1 ½ to 2. According to an eminent authority, “the advantages of anthracite over semi-bituminous coal are freedom from dust and smoke; both important in a war vessel, but particularly the latter.” The same writer goes on to demonstrate the commercial value of these qualities by saying, “They have to be paid for in the enormous excess of boiler required. So strongly marked is the inferiority of anthracite in this respect, that none of the transatlantic steamers voyaging to our ports use it for their return trips, although its cost per ton is fully one-third less [?] They prefer to pay this greater price rather than submit to the disadvantage of loss of speed or larger boiler.” It is well known to naval officers that our vessels on foreign cruises never obtain or try to obtain anthracite coal after leaving home. The fact is, that the neatness and cleanliness of our fine frigates has been obtained at a tremendous sacrifice of efficiency as war vessels. The question of smoke is more a bugbear than anything else in a high speed ship; for, in the first place, the best quality of Cumberland coal makes little or no smoke with properly designed furnaces and careful firing; the soft coal used in the British and French navies is not objected to on that account. In connection with the argument that a smoky fire, lasting even a few minutes, reveals the ship's presence to the enemy, it may be well to recall the fact that the blockade-runners put their faith in free- burning coal, and with the extra speed obtained from forcing the fires escaped in full view of the blockaders. The weight saved in the weight of machinery of the Chicago by designing on the basis of soft coal amounts to more than the whole weight of the armament, or to two days’ coal supply at full power, or other things being the same it would have
been impossible to carry a protective deck.
The type of boiler intended for the Chicago (see plate V) is new to the naval service, but is in successful operation in merchant steamers. There will be fourteen horizontal return-tubular boilers, designed to carry a working pressure of 100 lbs. per square inch, and constructed of steel which must conform to the “tests of steel for cruisers” prescribed by the Naval Advisory Board (see Appendix). They will be contained in two separate watertight compartments. The fire-rooms run fore and aft, and are to be 11 feet wide, except between the two forward boilers, which are canted inboard. There are to be two fixed smoke-pipes, each connecting with an up-take common to the boilers of each compartment. Each boiler will be 9 feet in external diameter, 9 ft. 10 in. in length on the bottom, and set inclining downwards from front to back, over a single furnace below the shell, being supported by girders of boiler plate lined with fire-brick. Each furnace is to have a grate about 7 ft. 8 in. wide and 7 ft. 6 in. long, making about 57 1/3 square feet, and aggregating 802 square feet in the fourteen boilers. The shells will be 5/8 in. and the heads ¾ in. and 5/8 in. The tubes will be of lap-welded iron. There is to be a steam drum in each smoke-pipe, concentric with it, and 9 feet in diameter, 9 feet long, 7/8 in. thick in shell; it is to have eight 18 in. and four 15 in. lap-welded flues passing through it.
The fire-rooms will be made airtight, and will be fitted with two large blowers each, which it is expected will be capable of maintaining a pressure of about an inch of water above the atmosphere. By this means the rate of combustion can be readily doubled when great speed is required for a short period.
The following advantages are claimed for these boilers over cylindrical marine boilers of ordinary construction having the same amount of grate and heating surface, viz. they occupy less space in the vessel, as a boiler 9 feet in diameter contains nearly the same grate surface as an ordinary boiler 12 feet in diameter. They are stronger and particularly well fitted for high pressures, as with the same thickness of shell the strength is in the inverse proportion of the diameter; and the large furnace flues, the weakest and least reliable portion of the ordinary boiler, are wanting here. The flat stayed surfaces, which are likewise a source of weakness, are of relatively small extent here. As the steam is generated to a great extent at the very bottom of the boiler and escapes readily from the furnace-crown, no mass of dead water can exist in it; the temperatures at top and bottom are nearly equal, and consequently the boiler is not liable to the destructive strains due to these differences of temperature arising with internal furnaces. The boilers are accessible for cleaning and repairs; the furnace-crown can be scaled with ease, as there are no seams or rivets in it. They are efficient steam generators and well adapted to high rates of combustion and forced draught, as the furnace is larger and higher than can be obtained in an ordinary cylindrical boiler. In consequence of the brick lining a high furnace temperature is maintained, favoring not only a perfect combustion of fuel, but increasing the efficiency of the heating surfaces.
The weight of the boiler, with its supports, furnaces, fittings, and water, is about the same as an ordinary boiler, but the amount of water carried is much less, and hence permits steam to be raised much quicker. Moreover, these boilers are cheaper to construct and keep in repair than ordinary boilers, on account of the simplicity of the casings and linings of the furnaces, which can be readily removed.
The question of the speed of these cruisers is one of the greatest importance and interest; but, on the other hand, an exceedingly delicate one to consider. The most, or, we may say, the only, satisfactory method of approaching it is by comparison with reliable trials and careful experiments upon similar vessels. The absence of any such data in the Navy makes it necessary to be very cautious. Ample power has been provided to obtain the designed speed, and if the machinery proves efficient and the screws suitable, it will not be a surprise if the Chicago makes nearly sixteen knots on the measured mile. When these vessels are finished and elaborate trials made of their speed and the efficiency of their machinery upon a measured distance, which is now the recognized standard of performance, then it will be possible to more carefully analyze the design, and, by giving to one part and taking from another, endeavor to improve in vessels which may follow. With this view the contracts have been carefully drawn, making it necessary to weigh each piece of material and every article or fitting that goes on board, both for the hull and machinery. In case of the Chicago the contractors guarantee, under penalty, that the weight of the machinery shall not exceed 937 tons.
Single Screw Steam Cruisers Boston and Atlanta.
Length between perpendiculars, 270 ft.
Length on water line, 276 ft.
Length over all, 283 ft.
Depth from garboard strake to under side of superstructure deck, 34 ft.
Height of main deck port sill from load water line, 11 ft.
Free board at extremities of superstructure, 9 ft.
Breadth—extreme, 42 ft.
Draught at load water line—mean, 16 ft. 10 in.
Displacement at water line, 3000 tons.
Area of plain sail, 10,400 sq. ft.
Complement of men, 230
Battery, four 8-inch and six 6-inch B.L.R.
Indicated horse power, 3500
Sea speed, 13 knots.
Capacity of coal bunkers, 580 tons.
Contract price for hull, machinery and fittings, exclusive of masts, spars, rigging, sails, boats, &c $618,000
The arrangement of the battery of the Boston and Atlanta, shown on plate VI, is certainly formidable and warlike in appearance, and the guns are mounted to command such an extensive train, or sweep of the horizon, that one of these vessels might prove no mean antagonist for a frigate of the Chicago class.
In vessels of the Boston class it is usual to have an open deck battery and a poop and topgallant forecastle, but here we may say that the poop and forecastle have been moved to the centre of the ship, forming a central superstructure, leaving the extremities clear and unobstructed.
Outside the forward port angle, and the after starboard angle of the superstructure an 8-inch long rifled gun will be mounted in a barbette about 3 feet high, built of 2 in. steel plates. The forward gun has a train from 40° abaft the beam on the port side sweeping the whole deck forward to 30° abaft the beam on the starboard side; similarly for the after gun. Within the superstructure six 6-inch B. L. R.'s will be mounted; two, on each broadside, with a train of 60° before and abaft the beam; one, forward in the starboard angle of the superstructure, may fight either through a forward or a broadside port, giving a total train of from 20° across the bow to 60° abaft the beam. The remaining gun is similarly mounted on the port side aft.
Comparing this disposition of the guns with that of an open deck battery with the two 8-inch and two 6 -inch in side half turrets, we have gained in strength of fire on each broadside by one 8-inch gun; the train of the 6-inch gun at the extremities has been much increased, besides the advantage of giving these guns a clean sweep across the bow and stern. The crews of the 6 -inch guns are protected from the fire of machine guns from an enemy's tops, and the guns cannot be fouled or disabled by falling spars and rigging. The manipulation of the guns is much simplified, and the service of ammunition much safer and more convenient, as the standing and running rigging leads to the superstructure deck. The side, at about the level of this deck, tumbles sharply home, plate VII, allowing convenient place for stowing the boats and manipulating the boat gear, which usually forms an obstruction to the fire of an open deck battery. The 8-inch guns will carry an armored mantlet as protection against machine gun fire.
The extremities of these vessels will not, of course, be so dry in heavy weather as if they had a forecastle and poop, but we should remember that every part of the deck is from 9 to 10 feet above the load water line, and that the men, instead of being exposed on an open deck or confined to a close berth deck, will have dry, airy quarters within the superstructure, which has a height seven feet in the clear beneath the beams. A bulkhead extends across the main deck abaft the after broadside guns. Abaft this on the starboard side is the captain's cabin. The space within the superstructure forward of this is devoted to the berthing of the men. It will be fitted with mess tables, seats, and chests for the crew. In all the cruisers particular attention has been paid to providing proper quarters and arrangements for the comfort and cleanliness of the men. The old-fashioned head will be replaced by the latest improvements; bathrooms and washrooms will be fitted and supplied with water, and a separate washroom will be fitted on the berth deck at the exit from the fire room for the use of the firemen. The officers' quarters are shown on the plan of the berth deck, the aftermost compartment being used as a bathroom.
Beneath the main deck the internal arrangements of the Boston and Atlanta are very similar to those beneath the gun deck of the Chicago. There are eight complete transverse bulkheads extending to the main deck, dividing the ship into nine main compartments, one less than the Chicago, as the Boston has a single screw and the engines occupy only one compartment.
The machinery spaces, extending over a length of 100 feet, are enclosed by a protective steel deck 1 ½ in. thick. Special structural arrangements have been made in order to so place this deck with reference to the water line as to afford the maximum protection to the buoyancy. The small draught of water of the Boston, two feet less than that of the Chicago, the larger diameter and length of the boilers, and the rapidly decreasing breadth of the vessel before and abaft the midship section, make it necessary to dispense with beams beneath the deck. The deck is stiffened at the sides, as shown on the midship section, by the transverse frames in the lower coal bunkers, the brackets in the upper, the fore and aft coal bunker bulkheads; and amidships by deep I girders. A light steel deck ¼ in. thick may be fitted over these girders in addition to the planking. One of the spaces marked A, between the flat and the deck proper, on each side will be utilized as a ventilating deck to lead air from the extremities of the vessel to the blowers amidships.
It may be allowable here to make a slight digression in reference to the draught of water. There, is a general opinion among naval officers and others that small draught is necessary and desirable for American men-of-war in order to permit them to enter our ports. The advantages of large draught are many and important; it is the most valuable and economical direction in which to increase the dimensions of ships, and particularly of war vessels, because the increased depth beneath the water line renders possible a more efficient disposition of, and greater protection to, the machinery, and greater immersion of the screws. It has been shown that it enables us to obtain forms of less resistance, thus favoring economical propulsion and high speeds. Again, deep draught tends to produce, what is of great importance to gunners, a steady ship in a seaway. In view of these manifest advantages it seems advisable to draw attention to the fact that the Chicago, drawing 20 feet 6 inches extreme draught, can with safety enter thirty-two ports on the Atlantic coast; the Boston and Atlanta, drawing 18 feet 6 inches aft, can enter only six ports from which the Chicago is debarred, namely. New Bedford, Fall River, New Haven, Washington, Annapolis and Tampa. If the Chicago's draught had been two feet greater she would be debarred from only two ports among the thirty-two, namely, Marblehead and Vineyard Haven, showing that an extreme draught of 22 feet might be adopted as safe, convenient and advantageous for cruising vessels.
To return to the internal arrangements, an inner bottom extends throughout the length of the machinery spaces, forming a watertight double bottom containing twelve watertight cells. Longitudinal bulkheads extend, as in the Chicago, on each side throughout the machinery space, forming side coal bunkers, and affording a coal armor of about 8 feet in thickness above the water line, and an average thickness of about 5 feet below it. The arrangement of watertight flats and bulkheads forward is similar to that of the Chicago, but aft it is not so convenient, as the best part of the stowage beneath the flat is taken up by the shaft alley. Altogether the Boston is divided into seventy-three watertight compartments. Great care has been exercised in arranging openings to these compartments that they may really be watertight, that is, the watertight doors have been made readily accessible, and arranged for manipulation from below or from the main deck. The systems of drainage and ventilation will be similar to and in every respect as complete as those in the Chicago. The total pumping power is 2000 tons per hour.
All the cruisers will be fitted with bilge keels. As doubts are frequently expressed as to their usefulness in limiting the rolling of ships, the following experiment may prove interesting. It was made by Mr. Froude upon the Greyhound, a vessel of 1100 tons displacement, with bilge keels, and the Perseus, a sister ship, without them; both vessels having been carefully trimmed to the same natural period. Mr. Froude says: “Three times we had them outside the breakwater at Plymouth in a tolerably rough sea. We could not, indeed, find a long rolling sea that would make the ships roll very regularly; but the upshot was that upon all occasions the Greyhound rolled just half as much as the Perseus rolled. The biggest roll we got out of the Perseus was about 23°, and the biggest roll we got out of the Greyhound was 11 ½°, and the periods were just the same. The addition of bilge keels does not materially augment the period, but it augments immensely the destructive power of the surrounding water in killing the oscillation that the wave originates.” In his evidence before the Committee on Designs of Ships of War (1871), Mr. Froude gave the following table of results of many observations upon the rolling in still water of a large model of the Devastation. The model was 1/16 the dimension of the ship and loaded to give the corresponding displacement, centre of gravity and distribution of weight, as in the ship itself.
The advantages obtained by the use of bilge keels are clearly demonstrated by these experiments, and are abundantly confirmed in practice. The increase of resistance due to their use is very small and hardly to be detected in its effect upon the speed.
The structural arrangements of the Boston and Atlanta are similar, with the exception of the protective deck, to those of the Chicago. There is very little change in the scantlings which are as follows for the principal parts, viz.:
Outside plating, including flat keel plates, 20 lbs. per sq. foot. Vertical keel plate, 17 ½ lbs. per sq. foot, 40 inches deep. The stem and stern posts will be of hammered scrap steel. Inner bottom, 105 lbs. per sq. foot, except at centre and on shoveling flat, where it will be 15 lbs. The transverse frames throughout the double bottom to be spaced 4 feet from centre to centre, and before and abaft, 3 feet 6 inches apart.
The frame angles will be 5” X 3” X 10 lbs. per foot, and the reverse angles 4” X 3” X 8 lbs. per foot, except at watertight frames and bulkheads, where the angles attaching them to the outer skin, keel, &c., will be 3” X 3” X 7 lbs. per foot. The frames and brackets will be cut short of the skin plating and secured to keel angle longitudinals by angles 2 ½” X 2 ½” X 4 ½ lbs. per foot. Reverse frames will be worked in short lengths between the keel and second longitudinal, but continuous from the latter to the protective deck and longitudinal coal bunker bulkhead. Forward and abaft the double bottom, the transverse frames will be composed of frame and reverse angles, both as within double bottom, and floor plates 12 ½ lbs. per sq. foot. Both angles will be continuous from the keel to the superstructure deck, except in wake of continuous longitudinals where the reverse bar will be worked in short lengths.
The first and second longitudinals from the keel are continuous and formed of plates 16 to 20 feet in length, weighing 12 ½ lbs. per sq. foot. The outer and inner angles are 3” X 3” X 7 lbs. per foot and 2 ½” X 2 ½” X 5 lbs. per foot. The other longitudinals are fitted as shown on the midship section.
Decks.
Superstructure deck.—There is no plating inside the hammock netting except a tie plate alongside the hatches.
Main deck.—Within the superstructure there will be a continuous stringer 33 inches broad and of 15 lbs. per sq. foot. The remainder of the deck is completely plated with steel weighing 122 lbs. per sq. foot.
Berth deck.—The protective plating over the engines and boilers will be made up of two thicknesses, of 30 lbs. per sq. foot each, and armored shields or bars will be fitted in all hatchways. Before and abaft the protective deck there will be a stringer 30 inches wide and weighing 15 pounds per sq. foot. The watertight platforms or orlop deck will have a complete steel deck 10 lbs. per sq. foot.
The rig of the Boston and Atlanta will be that of a brig to topgallant sails, making a spread of 10,400 sq. feet of plain sail. With a fair wind this disposition of the sail power will be more efficient than a bark rig, because in the latter the main course can seldom be set on account of the smoke pipe. In order that the fire of the forward guns should be unobstructed and the ram always ready for use head booms will be dispensed with.
The coal bunkers of the Boston and Atlanta have a capacity of 580 tons, but nearly 200 tons additional can be safely taken on board when necessary, thus giving an endurance of 2500 miles at full speed and 5300 miles at about 10 knots an hour.
Machinery.—The motive power of the Boston will be furnished by a three-cylinder, compound, horizontal, back acting engine of 3500 indicated horse-power. Plates IX and X show transverse sections of the machinery through high- and low-pressure cylinders, with the principal working parts.
The engine is to have one high-pressure cylinder of 54 in. diameter, and two low-pressure cylinders of 74 in. diameter, and each will have a piston stroke of 42 in.; the cylinders will be placed on the starboard side of the ship with their axes parallel, and 9 ft. 6 in. apart. Each cylinder will be steam jacketed and provided with two main valves and two expansion valves, the latter will be adjustable while the engine is in motion to cut off between the limits of one eighth and five-eighths of the stroke of the piston. The two main valves will have separate valve stems and connections, but, of course, are worked simultaneously from the same cross-head. By making the valve in two parts we gain in quality and workmanship and greater facility of examination. These valves are to be worked by means of eccentrics and Stephenson links acting through arms and rock shafts. There is a joint in the suspending-rod of the main link, which allows slight play in order to prevent any vibration being carried to the reversing gear. Much space is saved by making the eccentrics large and fitting them over the crank-shaft couplings. A vibrating beam formed of two straps of wrought iron and two sets of well proportioned gibs, keys and brasses, couples the link-block with the rock-shaft arm pin. The further end of this vibrating beam is hung from a radius bar, which is so adjusted that it regulates the motion of the link-block to correspond with that of the link, so that there will be little, if any, relative motion. The expansion valves are to be operated by separate eccentrics. The high-pressure exhaust will connect with the low-pressure cylinders, so as to pass the steam direct to the steam-chests; it will also be arranged to discharge direct into the condensers; and the low-pressure steam chests will be fitted with the requisite pipes for admitting the steam direct from the boilers or for exhausting the steam direct into the atmosphere.
The high-pressure piston will have one piston rod secured to a cross-tail, which will be coupled by four side rods with two other side rods to the cross-head. The low-pressure pistons are to have two rods coupled directly to the cross-heads; the latter are to be mounted on sleds, which are to run in troughs recessed in the pump chests. The connecting rods will be made with caps, secured by steel bolts.
The crank shaft is to be made in three separate interchangeable sections, and secured to each other and the line shafting by couplings forged on the shafts. The cranks for the low-pressure cylinders to be placed at an angle of 90° to each other, and that for the high-pressure cylinder to be set between the others and at angles of 135° from them. The shaft will be of steel, and 16 inches in diameter at the main journals. The arrangement of the pillow blocks of these journals is novel, and worthy of attention. Each pillow block will be made with a cast-iron pedestal, and two wrought-iron caps and wrought-iron and composition key-chocks above and below the brasses. By means of these and the stay rods, which take the place of the ordinary cast-iron framing, the brasses may be accurately adjusted in any direction, or readily removed.
There are to be two air and two circulating pumps, one of each coupled together and placed directly opposite the low-pressure cylinders; the pump chests will form supports for the condensers. The pumps will be horizontal, double-acting, and arranged to work independently or in connection with the main engine. Each couple, when working independently, will be operated through arms and a rock shaft by a horizontal direct-acting engine placed opposite the high-pressure cylinder. It will also be possible to make such connections that the circulating pumps shall be independent and the air pumps run by the main engine. There will be two condensers, with a total cooling surface of 8000 square feet.
The platform, with the gear for working the engine, will be placed between the condensers above the cross-head of the high-pressure cylinder; there will be suitable and convenient approaches to it from the deck, quarters and lower platform leading to the fire room and shaft alley.
The screw will be made of steel, and will have a diameter of 17 feet and a mean pitch of 20 feet, with four adjustable blades.
There are to be eight horizontal return tubular steel boilers, shown in plate XL They will be placed forward of the engines, four on each side of the vessel, divided into two groups by an athwart ship watertight bulkhead. There will be two standing smoke pipes, each connecting with an uptake common to four boilers. Each boiler is to be 11 ft. 8 in. in external diameter, and 9 ft. 9 in. long, and to have two cylindrical furnaces 43 in. in internal diameter. The furnaces will be of corrugated steel, if obtainable. Each furnace will have a grate surface of 25 square feet, aggregating 400 square feet in the eight boilers.
The boiler fittings are as usual in the service, except that the casting to contain the stop and safety valves will be made in one, thus necessitating but one opening in the boiler. The feed check valve is very conveniently arranged between two stop valves, so that it can be readily examined at any time.
It is the intention to utilize the advantages of forced draught and closed fire rooms, by which the power can be increased fifty per cent, for short periods. With this view there will be two blowers in each fire room, each capable of supplying 12,000 cubic feet of air per minute. Great care will be taken to make the fire rooms airtight.
Recent experiments have shown that, with air pressure in the fire
room of an inch to an inch and a-half of water above the atmosphere,
that 30 to 40 pounds of soft coal could be burned per square foot of grate
per hour, giving from 13 to 16 I.H.P. per square foot of grate surface.
There is nothing, however, particularly new in the employment
of airtight fire rooms, except in its use on such a large scale.
U. S. Dispatch Boat Dolphin.
Length between perpendiculars, 240 feet.
Length, extreme, 256.5 ft.
Breadth, molded, 31-85 ft.
Breadth extreme, 32 ft.
Depth from top of floors to top of main deck beams, 18.25 ft.
Depth from base line to top of main deck beams, 20.07 ft.
Top of main deck at side above load water-line, 6.28 ft.
Mean draught, 14-25 ft.
Displacement at mean draught, 1485 tons.
Area of plain sail,
Complement of men, 80
Battery—One 6-inch pivot, four revolving cannon.
Indicated horse power, 2300
Speed, 15 knots.
Capacity of coal bunkers, 310 tons.
Contract price for hull, machinery and fittings exclusive of masts, spars, rigging, sails, boats, &c., $315,000
The Dolphin, being intended for a dispatch vessel, capable of furnishing rapid communication from the seat of government to any point on the coast or the West India islands, or in event of the existence of a United States squadron, to act as fleet dispatch boat or flag-ship, the governing condition in the design has been high speed capable of being maintained for several days.
In order to obtain the most efficient and durable type of machinery, it was necessary to abandon any attempt at protection; thus we see from the drawings that the vessel is throughout of the ordinary merchant ship construction.
The Dolphin has a flush open spar deck without poop-cabin or forecastle; there will be a small central deck house near the cabin gangway and another around the boiler and engine hatches, otherwise the deck is uninterrupted fore and aft.
The armament is very light, consisting of one 6-inch B. L. R. mounted with a shifting pivot just forward of the fore-bridge, and four 47 mm, Hotchkiss revolving cannon mounted at the extremities of each bridge in fixed armored towers.
The Dolphin will be rigged as a three-masted schooner, the spars will be small and light, and there will be no head-gear; so that there will be nothing in the outward form of the vessel to prevent her from being fast and seaworthy.
The structural arrangements are those in practice in the construction of merchant vessels, except that unusual care has been taken to divide the hull into six watertight compartments by transverse bulkheads extending to the upper deck, and more than customary longitudinal strength is provided for. The bow is slightly ram-shaped and is made specially strong.
The principal scantlings and details of construction are as follows: The vertical middle line keel will be 20 lbs. per sq. foot. The side bars will be 9 inches wide and 22 ½ lbs. per sq. foot. The stem will be of best quality of hammered iron and 7 in. by 2 ½ in., except at the heel, where it is scarfed to the side-bar keels. The stern frame will be an iron forging of section about 10 in. by 41 ½ in.
The transverse frames are to be spaced 22 inches apart and be made up of a frame angle 4” X 3” X 9 lbs., reverse, an inner frame angle 3” X 2 ½” X6 lbs., both continuous from keel to main deck; and floor plates of 12 ½ lbs. per sq. foot and 18 inches deep amidships.
The flat sides or keelson plates on each side of and fitting closely against the vertical keel plate will be 12 in. wide and 15 lbs. per sq. foot. The continuous angles at the top of the keel will be 5” X 3”X 10 lbs. per lineal foot.
The first longitudinal from the keel is composed of an intercostal plate of 15 lbs. per sq. foot, extending 5 in. within the reverse bars, outer intercostal angles 3” X 2 ½” X 6 lbs. per lineal foot, and inner continuous angles each 5” X 3” X 10 lbs. The second longitudinal has an intercostal plate of 12 ½ lbs. per sq. foot, outer angle 3” X 2 ½” X 6 lbs. and inner continuous angles 5” X 3” X 10 lbs. The bilge stringer is simply composed of two continuous angles, each 5” X 3” X 10 lbs. per lineal foot.
The outside plating will be 17 ½ lbs. per sq. foot. This will be reduced to 15 lbs. at the extremities. The garboard strakes will be 25 lbs. per sq. foot, tapering to 20 lbs. The plating will be worked lap -jointed to within about two feet of the load water line and flush jointed above this height.
The plating and stringers on the main deck in wake of the engine and boiler hatches will be 15 lbs. per sq. foot ; forward and abaft of these the plating will be reduced to 10 lbs. The berth deck stringer will be about 30 in. wide and of 12 J lbs. per sq. foot.
The watertight flats forward and abaft of the machinery spaces will be formed of plates 10 lbs. per sq. foot jogged over the frames and attached to the plating by stapled angles 2 ½”X 2 ½”X 5 lbs. per lineal foot.
The bulkheads will be of the usual scantlings.
The Dolphin will have a steam steering engine, artificial ventilation, and will be lighted throughout by electric light and fitted with electric search lights, head lights, &c.
Machinery.—The Dolphin will have a single screw, actuated by a two-cylinder, compound, vertical, direct acting engine of 2300 indicated horse power.
The engine is to have one high-pressure cylinder of 42 in. diameter, and one low-pressure cylinder of 78 in. diameter, having 48 in. stroke of piston. The cylinders are to be placed directly over the crank shaft; each cylinder being supported by two wrought-iron columns, which are secured to the engine bed-plate, and by two cast-iron brackets, which form at the same time the cross-head guides and are secured to the condenser.
Each cylinder is to be made with a double shell, inclosing, in the case of the high-pressure cylinder, the receiver, and, in the case of the low-pressure cylinder, the steam-passage leading from the receiver to the steam chest on one side, and the exhaust-passage leading directly to the condenser on the other side. The total capacity of the receiver is to be about three and a half times the capacity of the high-pressure cylinder. Each cylinder will have an inner wearing cylinder cast separately, which, when secured in place, is to be surrounded by a jacket space to be filled with steam from the boilers.
The valve chests are to be placed on the forward side of the high-pressure cylinder and on the after side of the low-pressure cylinder.
Each cylinder will have a main slide-valve and a cut-off valve. The main slide-valves will be double ported, and worked by means of eccentrics and links coupled directly to the valve stems. The weight of each valve is to be counterbalanced by a piston working in a cylinder placed on the top of the steam-chest.
The cut-off valves are to slide on the back of the main slide-valves and to be adjustable, while the engine is in motion, to cut off between the limits of ¼ and 5/8 of the stroke of piston of the high-pressure cylinder, and of 1/3 and 5/8 of the stroke of piston of the low-pressure cylinder. They are to be operated by separate eccentrics coupled directly to the stems.
Each cylinder is to have one piston-rod, at the lower end of which the cross-head journal and the gibs for the cross-head guides are fitted. The crank shaft is to be “built up” and to have two cranks at right angles to each other; the forward or high-pressure cylinder crank being the leading one. Counter-balances are to be forged on the cranks. The crank-shaft is to be mounted on four journals having an aggregate length of 84 inches, and it is to be connected with the line-shafting by a disengaging coupling.
The crank-shaft pillow-blocks are to be made in one casting, forming the bed-plate of the engine, to which the columns supporting the cylinders and the brackets supporting the condenser are to be secured, and which is to be bolted directly to the engine frames forming a part of the hull of the vessel.
There is to be one surface condenser having an aggregate cooling surface of 4500 sq. feet. The tubes are to be placed athwart ships and so arranged as to be readily withdrawn and replaced. The refrigerating water, entering on the starboard side of the vessel, is to pass through the lower half and return through the upper half of the tubes, to be discharged through the outboard delivery valve on the starboard side of the vessel. The condenser is to be supported at each end by two brackets secured to the engine bed-plate.
The condenser is to be placed at the centre of engines below the cylinders, at such a height as to leave the centre main bearings accessible for examination and adjustment, and allow the shaft to be removed. To each side of the condenser are secured the brackets which support the cylinders.
The air-pump, circulating-pump, and feed-pumps are to be independent of the main engines. There is to be one horizontal double acting air-pump, and one horizontal double-acting circulating-pump, both worked directly from the piston of a steam cylinder placed between the two pumps. The circulating-pump will be capable of discharging 3300 gallons of water. There are to be two single-acting feed-pumps, secured to the sides of the steam cylinder, and worked from the cross-head of the circulating-pump. These pumps are to be placed in a fore-and-aft direction on the starboard side of the vessel, leaving a passage-way between them and the main engines. There are to be two bilge-pumps worked by an eccentric placed on the crank-shaft directly abaft the after main bearing. The bilge-pumps are to be single-acting plunger pumps, so arranged as to be thrown readily in and out of gear while the engine is in motion; they are to discharge the water into an outboard-delivery valve chamber on the port side of the vessel.
The steam reversing gear is to be placed on the port side of the engines. It is to consist of a steam cylinder bolted to the side of the condenser, the piston of which is to act by means of a link upon an arm of the reversing shaft, which is connected by means of arms and suspension rods with the links of the main slide-valves. The valve of the starting cylinder is to be operated by a hand lever from the platform on the starboard side of the engine.
There is to be a gallery running all around the engines on a level with the berth deck. The various valves, levers, and gears for working, regulating, and adjusting the main engines are to be operated from this gallery on the starboard side. There is also to be an upper gallery on a level with the spar deck.
The screw propeller is to have four adjustable blades, a diameter of 14 ft. 3 in. and a mean pitch of 21 ft. 4 in.
The boilers are to be cylindrical, braced for a working pressure of 100 lbs. per square inch above the atmosphere. They are to have an aggregate grate surface of 270 sq. feet and an aggregate water-heating surface of about 6600 sq. feet. They are to have internal cylindrical furnaces and horizontal fire tubes returning above the furnaces. Each furnace is to have separate back and front connections, the latter being provided with a damper.
There will be two single-end and two double-end boilers. The single-end boilers will have a diameter of 11 ft. and a length of 9 ft. 6 in. and contain two furnaces each. The double-end boilers will have a diameter of 11 ft. and a length of 18 ft. 3 in. and contain four furnaces each. The boilers will be placed with their longitudinal axes in the fore-and-aft direction of the vessel, the single-end boilers aft fronting the double-end boilers, with a fire-room 9 ft. 6 in. long between them. At the forward end of the double-end boilers there will be a fire-room 9 ft. long. On the starboard side there will be a passage way between the two fire-rooms and the engine-room.
There will be a vertical steam-drum 7 ft. 6 in. in diameter and 8 ft. 6 in. high, traversed by six flues 18 inches in diameter, and surrounded by the uptake.
The smoke-pipe will be stationary, 7 ft. 3 in. in diameter and 60 feet high above the level of the grates.
Provision is to be made for closing the fire-room hatches and other openings sufficiently tight to maintain an air-pressure equivalent to a head of water of one inch in the fire-rooms.
There will be two blowers in the after fire-room drawing the air directly from the engine-room and from a duct leading to the after part of the berth-deck, respectively; and one blower in the forward fire-room, taking the air from the forward part of the berth-deck. Each blower is to be capable of discharging 12,000 cubic feet of air per minute under a head of one inch of water at the discharge opening. The air is to be delivered directly into the fire-room. Each blower is to be driven by a separate direct-acting engine coupled to the shaft of the fan.
There is to be one horizontal steam pump, having a water piston 6 inches in diameter and 12 inches stroke, placed in the after fire-room on the port side. This pump is to be fitted for feeding and pumping out the boilers and for fire apparatus.
There is to be a distiller of 2000 gallons capacity per day, with tank, filter, and separate steam-pump, placed on a platform in the forward fire-room.
There will be two horizontal steam-pumps, each capable of delivering 1000 gallons of water per minute, connected for pumping out the watertight compartments, and also connected with sea-valves and fire apparatus. One of these pumps is to be placed on a platform in the forward fire-room, and the other is to be placed at the after end of engine-room on the port side.
There is to be an ash-hoisting engine fitted for each fire-room, and suitable arrangements are to be made for dumping the ashes on the spar-deck.
Two steam syphon-pumps with bilge connections are to be fitted, one in engine-room and one in after fire-room.
Through the courtesy of the Office of Naval Intelligence I am enabled to append to this paper a list of war vessels (see Appendix II) building at the present day, which shows that by far the larger part of the money employed in shipbuilding for war purposes is devoted to the construction of ironclads. There is no doubt that by adding to our navy more of the classes of cruisers just laid down and some of about 1500 tons displacement, we shall supply the most pressing need of the department; but it should not be forgotten that in order to take rank as a naval power, or to hold the sea against a naval power of fourth rank, for instance one of the South American governments, we must have armored seagoing vessels. By adding to our service unarmored vessels much larger than the Chicago, and even of tremendous speed, of which the advantage is in great measure fictitious, we should increase the expense of maintenance of the navy as much as by the addition of armored vessels of moderate size, but would not add to the naval power in anything like the same proportion.
It would have been eminently more satisfactory to the writer to be able to indulge in the more intelligible and careful discussion of many points not here mentioned, possible only in describing finished vessels. It has been the endeavor to present briefly such a description as the general interest of the public and naval officers demands in what is sincerely hoped to be a beginning of the reconstruction of the cruising fleet of the navy. During so long a period of inaction we have in great measure wasted the experience and prestige gained during the war. Opponents of naval expenditure in the direction of progress have always argued that when the opportunity or emergency arrived we should have profited by the experience and enormous expenditures of foreigners, but they are as ready when the time comes to allege “servile imitation” and decay of Yankee ingenuity, forgetful that this same fertility of invention for which the country is in many arts so distinguished, is the result of great demand, great production and resources. For instance, our excellence in wood-working machinery is not the result of spontaneous genius, but of the abundance of wood and its extensive use in thousands of various forms and devices. No doubt it is high time that we gained some experience for ourselves, for it can hardly be supposed that our officers can maintain the high state of efficiency claimed for them, by service in a fleet which is in every respect twenty-five years behind the times. However, it is confidently expected that through the cautious but sure progress of our ordnance officers in powder and guns, and the care which the department has been enabled, through the wisdom of Congress, to give to these designs, that the vessels will prove apposite to the needs of the service and at the same time compare favorably with others.
APPENDIX I.
TESTS OF STEEL FOR CRUISERS.
Navy Department,
Naval Advisory Board, June i8, 1883.
The following rules are prescribed in order to insure the fulfillment of the clause of the act of Congress of August 5th, 1882. “Such vessels ... to be constructed of steel, of domestic manufacture, having as near as may be a tensile strength of not less than sixty thousand pounds to the square inch, and a ductility in eight inches of not less than twenty-five per centum:”
I. All ship-plates, beams, angles, rivets, bolts, boiler-plates and stays, to be inspected and tested at the place of manufacture by a Naval Inspector of Material, and to be passed by him, subject to restrictions hereinafter mentioned, before acceptance by the shipbuilders, whether government or private, for incorporation into said vessels.
II. Every plate, beam, and angle, supplied for these vessels, to be clearly and indelibly stamped in two places, and with two separate brands: 1st. With that of the maker, which shall distinguish the name of the manufactory or company. 2d. With the regulation brand of the Naval Inspector of Material. The latter not to be stamped upon any of the above-mentioned material until it shall have passed the required inspection and tests, have been accepted by the Inspector, and have been stamped with the maker's brand.
In case of small articles passed in bulk, the above-mentioned brands shall be applied to the boxing or packing material of the objects.
No steel material to be received at the building yards for incorporation into the vessels except it bear, either upon its surface or that of its packing, both of these brands as evidence that it has passed the necessary government inspection.
SHIP-PLATES.
III. In every lot of 20 plates test pieces to be cut from two plates taken at random; two test pieces being cut from each plate, one in the direction of the rolling, and one at right angles to it, shaped according to the annexed sketch. These test pieces shall in no case be annealed.
The test pieces to be submitted to a direct tensile stress until they break, and in a machine of approved character.
The initial stress to be as near the elastic limit as possible; which limit is to be carefully determined by the Inspector in a special series of tests. The first load to be kept in continuous action for five minutes. Additional loads to be then added at intervals of time as nearly as possible equal, and separated by half a minute; the loads to produce a strain of 5000 pounds per square inch of original section of the test piece until the stress is about 50,000 pounds per square inch of original section, when the additional loads should be in increments not exceeding 1000 pounds.
An observation to be made of the corresponding elongation measured upon the original length of eight inches.
The final elongation to be that obtained at rupture. The loads applied shall never be calculated from the indications of the pressure gauge if a hydraulic press be used.
CONDITIONS OF ACCEPTANCE.
In order to be accepted the average of the four test pieces must show an ultimate tensile strength of at least 60,000 pounds per square inch of original section, and a final elongation in eight inches of not less than 23 per cent.
Lots of material which show a strength greater than 60,000 pounds per square inch will be accepted, provided the ductility remains at least 23 per cent.
CASES OF FAILURE.
If the average of these four tests pieces, numbered 1, 2, 3, 4 (called Test I), fall below either of the required limits, the plates from which pieces 1, 2, 3, 4 were cut shall be rejected, and Test II made, consisting of pieces 5 and 6, cut from a third plate; if the mean of the results of these two fall below either of the above limits the entire lot shall be rejected. If it be successful, Test III or the mean of pieces 7 and 8 cut from a fourth plate shall decide.
If in any of Tests I, II, III any single piece shows a tensile strength less than 58,000 pounds or a final elongation less than 21 per cent., the plate from which it was cut shall be rejected and that Test considered to have failed, regardless of its average.
QUENCHING TEST.
IV. A test piece shall be cut from each plate, angle or beam, and after heating to a cherry red, plunged in water at a temperature of 82° Fahrenheit. Thus prepared it must be possible to bend the pieces under a press or hammer so that they shall be doubled round a curve of which the diameter is not more than one and a half times the thickness of the plates tested without presenting any trace of cracking.
These test pieces must not have their sheared sides rounded off, the only treatment permitted being taking off the sharpness of the edges with a fine file.
ANGLES, BEAMS, BULB BARS, T BARS, &C.
V. In every lot of 20 angles or beams, &c., test pieces to be cut from the webs of two taken at random, one from each. These pieces to be fashioned in the same way, and to be subjected to the same tests, both tensile and quenching, and to fulfill the same requirements for acceptance as already prescribed for ship-plates.
Angle bars are to be subjected to the following additional tests: A piece cut from one bar in twenty to be opened out flat while cold under the hammer; a piece cut from another bar in the same lot shall be closed until the two sides touch, while cold; a piece from a third bar of the lot to be bent cold into a ring so that one of the sides of the angle bar shall be kept flat and the other side forming a cylinder, of which the internal diameter shall be equal to 3 ½ times the breadth of the sides which remains flat. The angle bars submitted to these tests must show neither cracks, clifts nor flaws.
Single T bars to be submitted to the following tests: A piece to be cut from the end of a bar taken at random from each lot of 20, and to be bent cold into a half ring, so that the web remaining in its own plane, the cross flanges shall form a half cylinder, of which the internal diameter shall equal four times the height of the web of the T bar.
At the end of another bar of the same lot the web to be split down its middle for a length equal three times its total depth, and a hole drilled at the end of the slit to prevent it spreading; the piece thus split to be opened out in its own plane, so as to make an angle of 45° with the rest, care to be taken that the part opened shall be kept straight, except that it must be joined to the rest of the bar by a bend of small radius.
Bulb bars are to be subjected to the same tests as those prescribed for T bars, except that in bending one or more heats may be used.
All bars submitted to these tests must show neither cracks, clifts nor flaws.
VI. One bar from every lot of 20 of the bars from which rivets are made shall be subject to the same tensile test as that required for the plate tests. All bars not fulfilling the requirements of tensile strength and elongation required for plates to be rejected.
From every lot of 500 pounds four rivets are to be taken at random and submitted to the following tests, one rivet to be used for each test: 1st. A rivet to be flattened out cold under the hammer to a thickness of one-half its diameter without showing cracks or flaws. 2d. A rivet to be flattened out hot under the hammer to a thickness one-third its diameter without showing cracks or flaws. 3d. A rivet to be bent cold into the form of a hook with parallel sides without showing cracks or flaws. 4th. A rivet to be tested by shearing by riveting it up to two pieces of steel which are to be submitted to a tensile strain, the rivet not to shear under a stress of less than 50,000 pounds per square inch.
BOILER PLATES.
VII. Each boiler plate must be subjected to the same tests and in the manner prescribed for ship plates. The ductility in eight inches must not be less than twenty-five per cent., and the ultimate tensile strength must not be less than 57,000 pounds and not more than 63,000 pounds, and the average at least 60,000 pounds.
The acceptance of material under these tests will not relieve the contractor from the necessity of making good any material which fails in working or may be rejected by the Inspector.