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18 MARINE REVIEW. [December 5, BALANCING MARINE ENGINES. FULL TEXT OF REAR ADMIRAL MELVILLE'S PAPER--HE BELIEVES THE MACALPINE SYSTEM TO BE THE BEST YET DEVISED-- AWARDED A SPECIAL PRIZE. Rear Admiral George Wallace Melville and Naval Constructor D. W. Taylor were the authors of the prize papers upon the subject "The Theo- retical and Practical Methods of Balancing Marine Engines," which were read at the recent meeting of the Society of Naval Architects and Marine Engineers in New York. The paper of Naval Constructor Taylor, to which was awarded the prize, was reproduced in a condensed form in the Review of Nov. 21. A special prize was given to Rear Admiral Melville's paper, which is reprinted herewith. Rear Admiral Melville's paper 'is devoted to the MacAlpine system, which he believes to be the best solu- tion of the problem of engine balancing to prevent hull vibration that has thus far appeared. Mr. John H. MacAlpine, the author of the system, had been hitherto associated in his work with Admiral Melville. The paper follows: _ The balancing of engines has been familiar to the engineering profes- sion for a great many years, particularly in locomotive engines and very high speed engines on shore. Within the past fifteen years, the subject has attracted much more attention among marine engineers on account of the effect of lack of balance in the engine in causing disagreeable vibra- L.P, Piston Fig. 15 > ip Fig. 14. | é "1 "STLPPisi oN La -- Ae ; j AEBS th moe et aS t | | / i: aN ipa : No oD Pop ale Fe a mol aha ye; : to \ fa pak Na : ae | 4 AN: A/S. ce ahs Seah : UL) > : x ao a Wi : : readily observed by everyone who has been on board ship to any great extent--one which has been clearly brought out by many writers on our present subject, For instance, Mr. Yarrow says, in his paper read in 1892 before the Institute of Naval Architects: "Some years since, we had a boat in which severe vibration occurred at 200, 400, 600, and 800 revolu- tions per minute, but there was none at the intermediate speeds of 300, 500, and 700." Thus there are the proverbial two sides to this question. The engine must supply impulses to the ship at or near the rate at which the ship itself would naturally vibrate. In other words, there must be synchronism between the speed of revolution of the engine and the free vibration of the ship. We may recall the old illustration of soldiers march- ing over a suspension bridge, where, if the step corresponds with the rate of vertical swing of the elastic structure, there is danger of breaking down the. bridge by producing a large vibration. If the rate of march is in- creased or diminished, the vibration of the bridge will diminish, but the usual practice is to make the soldiers "break step," so as to avoid any chance of the dangerous timing of the impulses. If, in the ship, we could always be sure of avoiding these troublesome speeds of revolution, there would be little need for accurately balancing engines. But it would be far too serious a restriction on the use of the engines, and it is impos- sible to predict with any sufficient degree of accuracy what the period of vibration of the ship will be. Besides, Mr. Yarrow's experiments bring out what is otherwise very well known, that the ship is capable of re- sponding to very different speeds of impulse--or, in other words, it may vibrate in many different ways, each having a period peculiar to itself. It is now fully recognized that a reciprocating engine of the usual z ALTERNATIVE PLANS. CLEARANCE FOR EXPANSION © OF CYLINDERS. 3) ~~ a -s 1s Sy a ae SECTION ON C.D, Fig. 13. Fig. 12. i Sif eee: > Pig. 8. Cylinders 27, 39, 56 and 80 in. by 48 in. stroke; boiler pressure, 200 lbs. Plate 1. tions in the hull. The matter has been brought before various engineering societies by some of the most accomplished leaders in the profession, and several systems have been actually applied in practice, while still others have been advanced with strong arguments to show their capacity to solve the problem of engine balancing and thereby that of hull vibration. The system which has thus far been applied to the greatest extent in practice is the Yarrow-Schlick-Tweedy system of: four cylinders with unequal crank angles and other arrangements for preventing vibration. While this system has been partly successful in accomplishing its aim, competent, observers on the ships to which it is fitted have found that it is not a complete solution of the problem, and, indeed, in some cases the vibration has been said to be almost as bad as with unbalanced engines. Mr. John H. MacAlpine, who has published a number of articles on this subject, is a personal friend of the writer, and has favored him with very complete information with respect to a system devised by Mr. MacAlpine, and which is a complete solution of the problem of balancing a marine engine. The members of this society are, of course, well aware that our navy has not adopted the Y. S. T. system of engine balancing, and as the writer | is in a position to know the reasons which have actuated the engineer-in- chief of the navy in his decision, he believes it will be of interest to present to the society a discusson of the various methods which; have been pro- posed or actually tried for balancing marine engines, including the Y..S, T. system, giving their merits and demerits, and going at considerable length into the MacAlpine system of balancing, which the writer believes to be the, best solution of the problem thus far presented. Obviously, in a dis- cussion which aims to give a history of the subject, prominence will be given not only to systems which are correct, but to those which are only partially so. : Unbalanced engines do not at all times vibrate a ship, but only at par- ticular speeds of revolution. This is a well-known fact which can be 08 Lc ENGINEER', IN CHIER, USN. --<-- CHIEF OF BUREAU OF STEAM ENGINEERING, - Basen Me a { kind does not supply merely one set of impulses at the same rate as it revolves, but a number of different sets of sensible magnitude and various periods. This makes the problem of preventing vibration by the adoption of a.particular speed of engine a greatly complicated one. Thus the whole problem is complicated mathematically, whether we consider the effect produced on the ship or the forces we have to deal with in the engines. If we can produce an engine which, when placed in the comparatively delicate elastic structure of the ship. will have all its inertia forces balanced, so.that they do not strain the ship, or if only those are transmitted to the hull which will not nearly synchronize in period with vibrations of a kind they could excite, consideration of the effect on the ship practically ceases to be part of the problem. To produce such a balanced engine we must adequately meet the comparatively complex dynamical conditions in the engine, and the solution must be not merely a theoretical one, but it must result in an engine which will not fall behind our best marine engines of today in steam consumption, and must be equal to them in first cost, upkeep, and practicability generally. : If it was merely a diagram or design on paper that was wanted, it would be easy to produce a great variety of 'theoretically' balanced engines. If, for instance, we were allowed to "suppose" an infinite con- necting rod, or to "suppose" that a slotted crosshead would work as well as a connecting rod, all we require is to maké an engine with three cranks in one plane, the center one standing up when the outer ones were point- ing down. Counterbalance the cranks and properly adjust, the reciprocat- ing weights, and' the balance'is perfect. The engine would'not start from its dead points, but that would be found to be' dnly oné- ofits minor defects. Such sentences are, no doubt, trivial. Unfortunately, they ate not more so than many of the proposals that have seriously been put forward in this connection, all of which we. may dismiss as impracticable without any further notice. We are not at liberty to make suppositions.