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The Modern Marine Boiler. A. B. WILLITS U, 8. N., IN ENGINEERING MAGAZINE, The marine engines, often things of beauty and always in- teresting in their steady, graceful and potent functions, receive all the praise when the ship is making or breaking a record. While it is not at all uncommon to find the ordinary commercial traveller versed in the technicalities of this portion of the ma- chinery, and able to discourse glibly on the relative "horse- power" of the leading transatlantic liners, it is seldom that he has much knowledge of the boilers, those vast factories and res- ervoirs of that power of which he speaks, and which, in their hot and grimy compartments forward, giving but few signs of the intense strain they are under during every moment of the run, perform a duty not in the remotest degree indicated by a share of the glory of a successful trip. It is probable, neverthe- less, that in the mechanical world to-day, more thought is being bestowed on the boilers than upon the engines proper; and far from being commonplace accessories, they are constructions of the most scientific character, combining in their proportions the results of the greatest range of experiment and deepest study. Each element is so carefully considered, both by itself and in its relation to the other parts, that the final outcome is an appar- atus of elegance to the professional eye, and one in which strength, durability, accessibility and efficient capacity are ad- al ONE OF THE MAIN BOILERS, UNITED STATES STEAMSHIP NEW YORK. MARINE REVIEW. proportions to sustain the pressure put upon them, something like ten inches in this case, which would be both impractical and absurd. Spherical ends would of course obviate bracing and ultra thickness, but the practical advantages of flat ends are retained by a scientific system of bracing. This boiler weighs about seventy tons and contains eight furnaces, and 1,148 tubes, aggregating nearly a mile and a half in length. 'These form the major part of the 5,200 square feet of heating surface, as they are always surrounded by water to be evaporated. 'The quantity of water necessary to fill the boiler to a proper steam- ing height is about thirty tons, yet under forced combustion, such as is always used for full power, this 1s converted into steam at the rate of % of a ton a minute, demanding a continu- ous supply from the pumps, at that rate, to maintain a safe level. The furnaces contain 165 square feet of grate, upon which is burned nearly three tons of coal per hour (about forty pounds per square foot per hour), with an air pressure of less than one- tenth of a pound per square inch above the atmosphere. 'The steam pressure carried is 160 pounds per square inch above the atmosphere, quite the usual pressure for triple-expansion en- gines, but when it is realized that this gives a total disruptive strain on the cylindrical shell of more than 6,500,000 pounds, it no longer appears as ordinary but rather terrific; a force, too, which is not evidenced by the placid exterior of this veritable torpedo. (From Engineering Magazine, New York.) justed to a nicety which satisfies the conditions imposed with regard to the production of a given power within a limited space and with a minimum weight of metal. The boiler depicted in an accompanying engraving represents one of the main boilers of the United States man-of-war New York, now in the course of completion in Philadelphia, and is of greater dimensions than any previously built in this country. It does not differ in size, in any marked degree, from the largest built abroad for the ocean greyhounds, although the latter usu- ally possess more heating surface in proportion to grate, to their economical advantage at full power 'The structure is 15 feet 9 inches in diameter, and 18 feet long, and is double-ended, having an exactly similar arrangement of furnaces and tubes in each end, only one of which is shown in the view. 'The tubes con- duct the hot gases and smoke of combustion from the backs of the furnaces to the fronts of the boiler, whence they are led to the smoke-pipe by light castings, attached after being placed on board ship, this type being styled the return fire tubular or more generally, the Scotch boiler. The material is open- hearth steel, subject to the closest inspection and severest tests before acceptance. The nine great sheets composing the cylin- der are more than' one-and-a-quarter inches thick (144) and weigh between five and six thousand pounds each. 'The flat- heads are thinner, but so closely stayed by heavy steel braces running from end to end, as to compensate for that. Indeed if wholly unstayed they would have to be of simply monstrous Taking the entire six main boilers of this ship, a brief sum- mary of data is at least impressive and suggestive of the impor- tance of these elements. Their net weight is more than 4co tons, and they contain about three quarters of an acre of heating surface, with eight-and-a half miles of tubes. Their forty-eight furnaces will consume more than 400 tons of coal a day and evaporate 140 tons of water an hour to produce the 16,500 horse- power needed to drive the vessel twenty knots an hour. They will occupy a floor-space in the depths of the ship, roo feet long by thirty-six feet wide (double that allotted to the main engines) and will require a force of a hundred men to properly attend to and manipulate them. A contemplation of these few facts makes it obvious to any one that a high degree of skill and effi- ciency on the part of the attendants is important and necessary and that the element of carelessness here would be as likely to cause havoc and disaster, as it would in the engine-room or on the bridge. Kternal vigilance is the watchword, responsibility and anxiety being ever present with the performance of this un- seen duty. It has been mentioned before that the boilers of the great ocean liners were proportioned with a larger ratio of heating surface to grate area than are those of men-of-war and it 1s to this fact that the former show a more economical perfor- mance, by obtaining a given power ona lower coal consumption Badly informed writers have used this to animadvert upon the designers or constructors of wat-ship machinery without troubling themselves to find a reason for the difference in results, ie SCORN ieee AD cee Rs saa a aah i sh