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442 the teeth running in opposite directions. In this way the end thrust due to the obliquity of the teeth is completely bal- anced. With a pair of wide-faced gears with straight teeth, it is hardly possible to cut the teeth with such accuracy and to align the shafts so perfectly as to get uniform contact throughout the en- tire length. Even if it were possible to secure the requisite degree of accuracy at the outset, it could not be permanently -maintained on account of the natural wear of the bearings. In general, the conditions are stich that a rigidly con- fined set of gears such as are common for moderate speeds and powers, is al- together inadmissable. In the design which has proven its sufficiency under severe and exhaustive tests, the smaller gear or pinion is mounted in what the inventors call a "floating frame." The frame which car- ries the bearings for the pinion is a heavy steel casting supported only at a single point midway between the bear- ings. The support is flexible so that the frame is free to oscillate in a verti- cal plane passing through the axis of the pinion, but is held securely against motion in any other direction. Further- more, the pinion is free to move end- wise in its bearings. Any tendency of the teeth to bear harder at one end of the gear than the other would tend to unbalance the respective end thrusts due to the right and left hand spirals of the teeth; but as the pinion cannot present any resistance to unbalanced end thrust, it constantly adjusts itself in the direction of its axis to the position corresponding to equilibrium between the opposing forces. This means that the tooth contact pressures are always auto- matically equalized. Functions of Floating Frame. If there are any minute irregularities . in the spacing of the teeth, which would tend to make the contact harder at one point than another in any part of the revolution, this tendency is defeated by the floating frame, the position of which about its central support or fulcrum is controlled solely by the pressures of the teeth of the pinion against the teeth of the large gear. Naturally, the float- ing frame always yields under the slight- est tendency of an unbalanced contact pressure in such a way as to transfer the smallest increment of unbalancing pres- sure, to another section of the gear that in the absence of the floating frame would be less inclined to take its full share of the stress. In short, the gears are self adjusting to relieve and equalize all abnormal strains, and are consequent- ly independent of the small inaccuracies that are impossible to eliminate in the an estimate. TAE MarINE REVIEW best commercial manufacturing opera- tions. The probable efficiency of the gear was naturally the most anxious question, as the operating conditions were so wholly unprecedented that there were no exist- ing data to enable one to even hazard The effect of a low effi- ciency would be more serious than a mere impairment of the economic per- formance of the installation, as the transmission losses would manifest them- selves in heating and destructive wear that would mean hopeless failure for the scheme in its entirety. In order to definitely settle the ques- tion as to the practicability of the gear, it was necessary to devise methods, and to design and construct special appli- ances for testing it under all of the con- ditions of load and speed that would probably obtain in actual commercial service. The dynamometer for applying and measuring the loads to which the gear was subjected, will, I trust, be considered sufficiently novel and interesting to warrant the extended description that will be found in an- other part of this publication. Considering the important bearing of the question of efficiency on the ultimate success of the gear, it is peculiarly gratifying to have found by repeated trial and careful meas- urement, that the transmission loss hoped for by Mr. Denny, has been divided by seven. To 'be exact, the efficiency reaches the almost unbe- lievable figure of 984 per cent, a result that is without doubt insep-- arably connected with the flexibility and self-adjusting character of the apparatus. It is needless to say that the gear is enclosed in a_ substantial casing, that adequate means are provided for its constant and efficient lubrica- tion, and that the ingeniously de- signed connections between the gear and the turbine effectually pre- vent the self-adjusting movements of the pinion from communicating any longitudinal or transverse stresses to the turbine shaft. Now that the mechanical operation of the gear is no longer a matter for speculation, it is interesting to consid- er its bearing on the design of turbine installations in ships, Turbines of Giant Cunarders. The turbines of the giant Cunarders, Mauretania and Lusitania, are supposed_ to be capable of developing 70,000 shaft horsepower. Even the comparatively low speed at which these turbines run is too high for maximum propeller efficiency. It is hardly possible that the propeller November, 1909 efficiency exceeds 55 per cent, which means that the actual effective propell- ing power is only about 38,500 horsepower. At a lower speed of revolution, well - within the capabilities of the reduction gear, a propeller could be made that would have an efficiency of not less than 65 per cent. With this improved efficiency, the shaft horsepower required for the same effective propelling power would be somewhat less than 57,000, a saving 'of 'almost 15 per. cent. "Fhis means that without sacrificing in the smallest degree the remarkable speed of. these vessels, the boiler equipment could be reduced about one-seventh, as well as the amount of coal burned on each voyage. This would not only result in a very marked saving in cap- ital investment and operating expenses, but would add many tons to the cargo carrying capacity, and add. correspond- ingly to the earning power. : But this" estimate; large as it 4s, is still too modest. With the turbine and the propeller direct connected so that both revolve at the same speed, not only is it necessary to sacrifice the efficiency of the propeller, but the ef- ficiency of the turbine as well. For equal efficiencies in any two turbines, the number of rows of blades is, roughly speaking, inversely propor- - tional to the squares of the respective peripheral speeds of the rotating ele- ments. The peripheral speed of the rotating elements in the turbines of the Mauretania and Lusitania, is only one-third of the speed common in large turbines used on 'land. This would mean that to obtain the efficiencies common to the latter, the former would require approximately nine times as many rows of blades, which would nmiake a machine of prohibitive length. To maintain the same speed of revolu- tion and increase the peripheral speed of the turbines of these vessels to the point common in land practice the rotors would have to be nearly 40 ft. in diameter, which is manifestly beyond the shadow of possibility. Steam Consumption of the Cunarders. From the best information obtainable, it is believed that the steam consump- tion of the turbines of the Mauretania and Lusitania cannot be less than 14.5 lb. per shaft horsepower per hour, while it has been demonstrated beyond question that turbines of similar capacity operating at speeds which the reduction gear . makes possible for marine service, the steam consumption does not exceed 11 lb. per shaft horsepower per hour, This mean: that the boiler capacity could be fur- ther reduced from the first estimate of 60,000 horsepower to about 45,000 horse- Sei ck al ma AOC ae a ek ae a cat cian cg