Statement of dimensions, weights, and other particulars of Her Majesty's ship Derastation, as completed for sea, and as estimated at various dates. *This includes the superstructure added in January, 1871, and the additions recommended by the committee on designs. Estimated consumption of coal in the Devastation, at speeds of ten and twelve knots. 9, 062. 0 9, 008. 0 8,872.0 9.295.0 26.2 54.0 218.0 Statement in Mr. Reed's memorandum on new designs for iron-clad ships, dated 2d March, 1869, page 311, report of committee on desigus of ships, (printed for Parliament). Coal carried. 1,400 tons: Coal carried, 1,600 tons; Calculations based on results of measured-mile trial, 31st October, 1872..... Coal carried, 1,400 tons: Calculations based on results of measured-mile trial, 31st October, 1872. Calculations based on six hours' trial, 15th April, 1873. Coal carried, 1,600 tons : Calculations based on six hours' trial, 15th April, 1873.. MOTIVE MACHINERY. The Devastation is propelled by twin screws, each driven by an independent pair of engines. These engines, which have been constructed by Messrs. John Penn and Sons, of Greenwich, are of that firm's direct-acting trunk type, contracted for prior to the adoption of compound engines, and they have cylinders 88 inches in diameter, and trunks 36 inches in diameter; the trunks reducing the effective area of the pistons to that due to a diameter of 80 inches. The cylinders are steam-jacketed, both at sides and ends, and the stroke of pistons is 3 feet 3 inches. The engines are fitted with expansion gear, which enables the steam to be cut off at any required part of the stroke. The main slide-valves are double-ported, and fitted with an equilibrium ring. The expansion-valves are of the gridiron form, with a variable stroke and cut-off. The admission of steam to the engines is regulated by equilibrium valves, which are worked by screws and suitable gearing, led away to the starting platform. To insure ready handling of the engines, small auxiliary slide-valves are fitted to each cylinder. Each pair of engines is fitted with a surface-condenser containing 5,432 inch tubes, 6 feet 3 inches long; the condensing surface for each pair of engines being thus 6,710 square feet. The tubes are packed with screwed glands and tape packing. The air,pumps and the circulating-pumps are double-acting, and are worked direct from the pistons. The condensing water is drawn through the tubes and the steam admitted to the outside. The crank-shafts are in two pieces, with solid couplings forged on. The turning-gear consists of a wormwheel and worm, worked by hand by means of a long ratchet lever. The disconnecting coupling is fitted with four steel pins, which can be drawn out of gear by means of screws and ratchet spanners. The thrust of the propellers is taken by a bearing fitted with ten movable collars. The screw propellers are 17 feet 6 inches in diameter, and have 19 feet 6 inches pitch, and are so fitted that the pitch can be varied from 17 feet to 22 feet. The number of blades to each is four, and the propellers are formed on the Griffiths principle. The boilers are eight in number, of the old kind, containing thirty-two furnaces, the four boilers in the forward fire-room having four furnaces each, while of the four boilers in the after fire-room two have three and two have five furnaces each. The length of bars is 6 feet 6 inches, and the width of furnaces 3 feet 2 inches, the total fire-grate area being thus 742 square feet. The boilers contain in all 2,592 tubes 3 inches in diameter and 6 feet long. The working pressure of steam is 30 pounds per square inch. The total heating surface is 17,806 square feet. A superheater is fixed in each chimney, of which there are two, the total superheating surface exposed being 1,866 square feet. The chimneys are telescopic, and are fitted with hoisting-gear and shell-proof gratings at the bottom. The length in the ship occupied by the engines is 32 feet, and that by the boilers 80 feet, this latter length being divided into two equal compartments, separated from the engines and each other by water-tight bulkheads. Telegraphs are fitted between the engine-rooms and the bridge, and, in addition to the ordinary means of ventilation, fans are fitted, driven by independent engines. A powerful fire-engine is provided with pipes leading to all parts of the ship. Engines are also fixed for moving the capstans and hoisting the ashes. The weight of engines and boilers complete, with water in boilers and condensers, and including spare gear and all the fittings above enumerated, is 985 tons, or but 2.96 ewt. per indicated horse-power developed when working at full power on the official trial. The following results were obtained on the official trial, September 2, 1872: Draught of water forward Draught of water aft..... Immersion of upper edge of screw. Pressure of steam in engine-room, 27 pounds. Revolutions Mean pressure in cylinders, starboard. Mean pressure in cylinders, port.. Indicated horse-power, port. Speed of vessel ... Immersed midship section, 1,460 square feet at 26 feet 5 inches draught. Co-efficient, 582. During the full-power trial the total power developed by the two pairs of engines was thus 6,637.71 horse-power, and the areas of grate surface and condensing surface, per indicated horse-power, were as follows: Area per indicated horse-power developed on full power trial: The trial-cruises of the Devastation, to ascertain the degree of success attained in the design as an engine of war, as well as her sea-going qualities, were made in the summer of 1873; and it may be said with confidence that never before did the proceedings of any single vessel elicit so large an amount of public interest as did those of this ship. The novelty of her design as an ocean-cruising man-of-war, her odd appearance, and her fighting power, formed continued topics of discussion in the scientific and other papers, but the real source of interest to the English people was doubtless to be found in the fact that the vessel was looked upon by the general public as belonging to the same type as the unfortunate Captain. Hence, notwithstanding the vital points of differ ence between the two vessels, to which attention had been repeatedly drawn, her trials were watched with an interest amounting almost to anxiety. The preliminary trials had reference principally to the performance of the engines, boilers, turrets, and other machinery. The great importance of the first of these will be evident, since the vessel is an oceangoing cruiser, without masts and sails-i. e., she is entirely dependent on her engines for propulsion. As has been seen, at the full-speed measured-mile trial a speed of 13.8 knots per hour was obtained, the engines indicating 6,637 horse-power; and from a series of continuous steaming trials at various speeds, it was shown, with her full supply of coal, what distances could be run, the results of which are recorded above. The gunnery trials were made subsequently at the usual testing. ground off the Isle of Wight. The guns are capable of being raised and lowered by hydraulic pressure through a height of 20 inches, and may be thus placed for firing so as to obtain any desirable degree of elevation or depression in combination with small port holes. The projectiles used in the trials were 700 pound Palliser cored shot, with a battering charge of 110 pounds of pebble-powder. At the trial the guns were fired first with extreme elevation, and then with extreme depression in all directions around the ship. During two or three trials made by the vessel off Portland and Queenstown, the difficulty of judging of her behavior, with reference to the seas inducing that behavior, as compared with the behavior of ships of ordinary form under similar circumstances, suggested the desirability of prosecuting the ocean trials in company with some ship or ships of about the same dimensions but of less unusual type. Carrying out this idea, the vessel was placed in company with the Agincourt and Sultan, and thus made to form part of a division of the channel squadron. The Agincourt is one of the early iron-clads, having been built in 1862-65. She is 400 feet long, and is somewhat heavily rigged with five masts. She is completely protected by armor 5 inches thick. Her armament consists of twentyeight guns in a long row, after the old style of frigates; but although the thickness of her armor and the weight of her guns are now out of date, she is claimed to be one of the best sea-boats in the whole fleet. The Sultan, on the other hand, is one of the more modern iron-clads. She is short, not much longer than the Devastation, and is rigged with three masts as a ship. Her armament, consisting of twelve guns, is mounted in a central two-storied battery and protected by thick armor. The water-line also is protected by a belt of thick armor. A scientific gentleman who was on board the Devastation during these sea-trials wrote a highly interesting and valuable account of the proceedings, and, as a matter of interest in relation to the behavior of this class of vessels at sea, the notable points of this letter are extracted as follows: The squadron, consisting of these three vessels, put to sea from Plymouth Sound at the end of Angust, 1873; the programme laid down being to proceed to Bear Haven, on the southwest coast of Ireland, and from this point make occasional cruises into the open Atlantic, as suitable weather should occur. This programme was pretty strictly adhered to in all respects. The vessels arrived and anchored off Bear Haven on the 2d of September, after a cruise of four days, during which many points of interest came out, although no very heavy weather was met with. For purposes of comparison in pitching and lifting, &c., the Sultan had the height of the Devastation's upper deck at side painted on her in a broad white stripe, so that the behavior of the two ships might be quickly appreciated apart from the records of instruments. The lowness of the extremities of the Devastation gives a great deal of interest to the pitching and lifting (really the longitudinal rolling) of the vessel. Two trials were made, one on the 9th and the other on the 15th of September. On the first of these occasions, she was accompanied by the Sultan only, and on the second she was accompanied by the Agincourt only. The seas met with on the 9th of September were lumpy and irregular, the wind having shifted somewhat suddenly during the previous night. Having got well out to sea, about 40 miles off land, the wind was found to be blowing rather north of west with the force of a moderate gale, its speed varying from 40 to 45 miles per hour; and the largest of the waves were found to vary from 300 to 350 feet in length from crest to crest, occasionally reaching 400 feet-the greatest heights from Follow to crest being 15 and 16 feet. Going head to sea, at from six to seven knots, both vessels pitched considerably; the Devastation, however, had the best of it, pitching through smaller angles than the Sultan. The latter vessel was remarkably lively; at one moment she was to be seen with her fore-foot completely out of water, and the next with her bow dipped down to so great an extent that it was difficult to see from the flying deck of the Devastation-although the ships were pretty close together-whether the sea did not really break inboard; and this notwithstanding that the bow of the Sultan rises forward some 30 feet above the surface of the water. On the other hand, the forecastle-deck of the Derastation was repeatedly swept by the seas, to each of which she rose with surprising readiness; indeed, it invariably happened that the seas broke upon her during the upward journey of the bow, and there is no doubt it is to this fact that her moderate pitching was mainly due, as the weight of the water on the forecastle-deck during the short period it remained there acted as a retarding force. preventing the bow from lifting as high as it otherwise would, and this of course limited the succeeding pitch, and so on. The maximum angle pitched through on this occasion, i. e., the angle between the extreme elevation and depression of the bow, was 7. Each vessel behaved extremely well when placed broadside onto the sea, rolling very little. The trial of the ship on the 15th of September, in company with the Agincourt, was by far the most severe of any. Early in the morning the vessel got under weigh and steamed out to sea, accompanied by the Agincourt. The wind was blowing with considerable force from the northwest, while the sea was at times very regular, long, and undulating; just the sort to test the rolling propensities of a ship, but scarcely long enough to be most effective in doing so, either in case of the Devastation or Agincourt. The largest waves ranged from 400 to 650 feet long, and from 20 to 26 feet high. The ships were tried in almost every position with regard to the direction of the sea, and at various speeds, the result in point of comparison being extremely interesting. and, so far as the Devastation was concerned, very satisfactory. With the sea dead ahead, and proceeding at about seven knots, the Devastation pitched rather more than the Agincourt, although the great length of the latter compared with that of the former caused her bow to rise and fall through a much greater height, giving her the appearance of pitching through a greater, angle. The usual angles pitched through by the Devastation, measuring the whole arc from out to out, were from 50 to; the maximum angle pitched through was, however, 11°. The scene from the fore end of the flying deck when the vessel was thus going head to sea, was very imposing. There was repeatedly a rush of water over the forecastle, the various fittings, riding-bitts, capstan, anchors, &c., churning it up into a beautiful cataract of foam; while occasionally a wall of water would appear to rise up in front of the vessel, and dashing on board in the most threatening style, as though it would carry all before it. rushed aft against the fore turret with great violence, and, after throwing a cloud of heavy spray off the turret into the air, dividing into two, pass overboard on either side. All the hatchways leading below from the upper deck were closed; it was not, however, thought necessary to close the doors in the sides of the trunks leading up from the main hatchways to the flying deck, most of the men on deck preferring to remain here under the overhang of the flying deck. It was quite the exception for the water coming over the bow to get much abaft the fore turret; but this, however, occurred occasionally. The foremost turret makes a most perfect breakwater; it receives with impunity the force of the water, which, after spending itself against it, glances off overboard, leav ing two-thirds of the deck seldom wetted. There was one sea which came on board. while thus proceeding head to sea, which was much heavier than any other; it rose in front of the vessel some ten or twelve feet above the forecastle, and broke on the deck with great force, for the moment completely swamping the fore end of the vessel. A mass of broken water swept up over the top of the fore turret, and heavy volumes of spray extended the whole length of the flying deck, some small portion of it even finding its way down the funnel-hatchway-which had been left uncovered-into the fore stokehole. It should be borne in mind that the angles pitched through, given above, do not measure the inclination of the ship to the surface of the water, but only her inclination to the true vertical. Pitching and lifting are produced by the vessel endeavor ing to follow the slope of the waves, or, roughly speaking, to keep her displacement the same as in still water, both as to volume and to longitudinal distribution. As to the depressing effect of the water on the bow, a layer of water one foot deep over the entire forecastle exerts a pressure of 65 tons; this will produce a change of trim of 11 inches, together with an increase in the mean draught of 14 inches; i... the draught of water forward will be increased by 74 inches, while that aft will be diminished by 34 inches. A layer two feet thick will have double this effect; one three feet thick will have treble the effect, and so on up to a considerable angle. This follows from the fact that the front slope of the longitudinal curve of stability, up to a considerable angle, is very nearly straight. Hence the effect, even of a large body of water passing over the forecastle, tending to make the vessel dive down head foremost, is small and of no importance. It modifies, however, the transverse stability. When proceeding head to sea there was no appreciable rolling motion. With the wind and sea on the bow she pitched considerably less than when going head to sea, but rolled through 50 or 6°. With the wind and sea abeam. lying passively in the trough of the waves, the maximum angle rolled through was 14from port to starboard, 6 to the windward, and 74° to leeward, and this without perceptible pitching. When, however, proceeding at about 74 knots, with the wind and sea on her quarter, she rolled through 274° from port to starboard, 13 off the perpendicular to windward, and 144 off the perpendicular to leeward, beside also pitching through some 4 or 5. This is by far the greatest augle she has ever rolled |