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1901.] MARINE REVIEW. | 23 supplant the reciprocating engine. With.a view to give it a fair trial, Messrs. Denny built the excursion steamer King Edward, which has recent- ly. been put in service'on the river Clyde. Nearly all of the published ac- counts of trial trips of torpedo-boats have called particular attention to the marked absence of vibration at high speeds, so that this has already been advanced as a strong argument in favor of the adoption of the turbine. In addition to others which have been given, it should be stated at once that the turbine is perfectly balanced, for it would be impossible to run it at the high speeds necessary, unless it were in perfect dynamical balance. It is to be noted, however, that there are some very serious drawbacks to the steam turbine, as far as it has now been developed, for general use as a marine engine. One is the difficulty of reversing, and, as is well known, the vessel is driven astern not by the same turbines which give the ahead motion, but by independent ones which, from the necessities of the case, are much smaller and give only a relatively low speed. It has been asserted by many that the recent loss of the Viper, from whose performances so much information was expected, was on account of this lack of full power for reversing. Another objection is the decided lack of economy at very low powers. 'While this might not apply to the large liners which run at nearly constant speed throughout the voyage, it is a very real objec- tion to use on war vessels which, during most of their cruising run at about one-tenth of their full power. It is true that Mr. Parsons has pro- posed to increase the efficiency at low powers by fitting small triple- expansion engines forward of the turbines with a clutch connection to the main shaft. This proposal, however, can hardly receive much approval, for the reason that it would introduce altogether too much complication of machinery.. I understand, moreover, that while the turbine itself is com- pletely balanced and there is no vibration of the ship forward of the tur- bines, experience on the King Edward has shown that there is a decided vibration which increases from amidships aft. In the saloons, especially in the lower or dining saloon, the vibration and noise are very great, and, indeed, at the after end of the saloon the vibration is said to be almost unbearable. In this respect, this vessel is probably the worst on the Clyde. This vibration is partly due to the propellers, for it must be remembered Crank "IIT ~ 1:P. ond H-P. Gyls. tandem Crank Iv --~ 229 Int: Cyl. Crank ID -- L.Pand HP Gyls. tandem Crank I -- I Int. cyl ] Forward» =a st =e | ee 400mm) +I! 6-9 joo) ee 4a ? Plate 3. | Crank Centers Fis. D that the speed of revolution is abnormal compared with that of ordinary vessels, and a degree of balance which would be considered perfect in a propeller running at ordinary speed would be inadmissible for these very high-speed cases. In any event, the steam turbine is at present entirely in the experimental stage, and whatever its future development may be there can be no question that we shall go on building reciprocating engines for a great many years to come.. Consequently, from the standpoint of actual practice, the turbine cannot be considered a' practical solution of the bal- ancing question. ee ste Let us now consider Mr. MacAlpine's solution of the vibration problem, taking largely ¢s a guide his recent paper, read before the Institute of Naval Architects this year in their summer meetings in Glasgow. We have seen, earlier in this paper, that only partial balance can be attained by direct-connected four-crank engines; and that, though the solution with five and six-crank engines is much more nearly perfect, there are great practical objections to their general adoption, 'The complete solution, then, is not to be attained by direct-connected engines of the usual type. There is still one solution with the connecting-rod engine, and it is unique. Add to the right-hand side of equation (14) an expression-- mw?r poe (cos 9 + .2540 cos 2 --.0041 cos 49-+.00007 cos 69 + etc.) (16) & Make MR=mr and we at once have PO, This solution is realized with the most complete success in one of the Watson and Billetop balanced engines. It is a four-cylinder engine. Pairs of cylinders are placed exactly in line, but on opposite sides of the crank shaft. The cranks for opposite cylinders are exactly opposite, so. that the motions of the pistons are exactly the same, but in opposite direc- tions. This makes the addition of expression (16) to the corresponding expression in (14), as directed above. In Engineering of July 5, 1901,.p. 7, Mr, Billetop writes: = | ae "During the tests, the engines were not held down by bolts.or fixtures of any kind, and a glass filled with water and. placed on top. of the.cylinders. de not show the slightest surface tremor when running under. those con- itions. as Fig. 6 also shows, roughly, a design of en- rod. The rest of the lower moving parts are balanced by the oppositely moving upper parts. By making these adjustments correct, the ver- tical and horizontal balance can be made exact, _ Figs. 7 to 18, Plate 1, show a design which Mr, MacAlpine gives in his 'paper, but which he has now improved on. He points out that 2 the motion of the back piston is not absolutely OS the reverse of that of the piston over the \ & ie 'shaft. The difference of displacement is, how- ever, never more than a very small fraction of 0 'an inch, and I retain the design as a very ap- proximate solution, though I am entirely satisfied that the modification in Figs. 19 to 21, Plate 2, is to be preferred, not only because it gives a perfectly exact solution, but for purely practical questions of design. Figs. 22 to 27, Plate 3, show another form of exact solution only suitable for merchant ships where there is ample headroom. _ In each of these designs a comparatively AAG light counterbalance on the crank exactly bal- ances it and the other parts revolving with it. The horizontal forces are thus balanced. The reciprocating masses, moving oppositely in the = pairs of cylinders, can also be adjusted so as KO to balance. In the designs shown the stroke gine in which this solution is realized.. The counterbalance on the shaft balances the inertia of the crank and part of the connecting b : of piston for each cylinder is equal, so that 2 t what is required is to make these oppositely reciprocating masses exactly equal. The cal- Fig. 6. : culations for the design, Figs. 7 to 18, Plate 1, I append, to bring out all the details that have to be attended to. I do not give the figures for the other designs, as these given are inserted merely to act as a guide to those calculations which will have to be repeated for each new design as it is made: But we are left with an unbalanced inertia torsional couple, since the connected pairs of pistons, etc., do not move in the same vertical line. By placing the cylinders tandem or adding a third cylinder on the other side of the vertical line through the shaft, connecting it also by a lever, this increase. of the unbalanced torsional couple is avoided. But these arrange- ments are not to be commended for shipboard, and I will show that the simpler design is justified by the small effect of the unbalanced torsional couple. 'This effect will be to vibrate the ship torsionally about a longi- Wan [si "ARRANGEMENT OF STEAM cou ECTIONS. Fig. 22. Fig. 23. Plate 4. Cylinders 27, 39, 56..and 80 in. by 48 in. stroke; boiler pressure, 200 Ibs. tudinal axis. We will require to examine carefully the magnitude of this vibration since the admissibility of the engine as a solution of the problem depends on its being exceedingly small. This magnitude is, happily, very easily predicted. We will leave this question till near the end of the paper and give first the nécessary adjustments for exact vertical and horizontal balatice, -- -- : . tee "Cylinders 27 in., 39 in., 56 in., and 80 in. diameter,. Y° > ~ "Stroke, 48 in: . en ee "Boiler pressure, 200 lbs. per square inch. "Designed piston speed, 900 ft. per minute. "Revolutions, 112.5 per minute.