DISCUSSION ON MAY MEETING PAPERS. 41 



points and possessed of a high degree of rigidity within itself, such as may be approxi- 

 mately with the two or three plane gears, with the additional precaution of very accu- 

 rately machined bearings and journals with practically perfect alignment, would undoubt- 

 edly operate successfully under the varying conditions to which this ship's hull is subjected. 

 It would seem much simpler, however, to recognize the fact that the gear casing is prone 

 to distort and that it is practically impossible to obtain, to say nothing of maintain, the 

 desired degree of alignment between pinions and gears, and to employ a structure which 

 in itself compensates for these factors. Several instances have been reported where the 

 bearings have been seriously worn, due to failure of oil supply or dirt in the oil, causing 

 change in alignment between pinion and the pinion supporting structure of as much as 

 one-quarter of an inch without any noticeable effect upon the gear tooth. It is needless 

 to say that these cases were where the flexible pinion support was employed. This par- 

 ticular device for giving flexibility, as pointed out in Mr. Hodgkinson's paper above re- 

 ferred to, has been tried out in service in many instances since 1911 and should, there- 

 fore, be considered as somewhat more than a laboratory experiment. Practically every 

 gear designer at this time recognizes the inherited difficulties in connection with the de- 

 sign of marine gearing and is making a strong effort in one way or another to introduce 

 some form of compensating flexibility. 



While it is true that comparatively few single-plane type double-reduction gears have 

 traveled over 100,000 miles, a large number employing the flexibly supported pinion 

 frame have traveled in excess of 70,000 miles and show no evidence of not being able to 

 operate many times this distance without replacement. By incorporating the flexible sup- 

 port, this type of gear is reliable; and it offers the very great added advantage of acces- 

 sibility. In Mr. Hodgkinson's paper of November 14, 1918, Fig. 4, are shown curves 

 of tooth pressures in pounds per inch of face for varying diameters of pinions, and all 

 the gears noted on this curve by the circles show no evidence of requiring replacement 

 within many hundreds of thousands of miles. The tooth pressures for the rigid bearing 

 gears on this curve correspond vvith those proposed by the author of this paper, and the 

 question would seem to arise: Why limit the tooth pressures for the larger size gears to 

 approximately half of what may safely be allowed? 



The question of noise with the steel gear covers was one that was active with the 

 Westinghouse Company some time ago. Tests were made in steel, cast-iron, wooden and 

 lagged steel covers, and while the lagged covers gave some relief from a rather excessive 

 noise, the final solution of the problem permitted the use of the bare steel covers with 

 quieter gears than had heretofore been considered practical. A surgical operation was 

 found to be better than the "application of a poultice." The experience with gears built 

 by the Westinghouse Company does not bear out the author's contention that gears fitted 

 in the stern of the ship deteriorate more rapidly than those fitted amidships. Out of 

 many examples of both types it has been found that there is apparently no difference in 

 choice with respect to the two locations. The satisfactory operation of these gears when 

 placed in the stern is undoubtedly due to the flexible support of the pinion frame. 



We would add here that in the case of one gear, the steamer Hisco came part way 

 across the Atlantic with the tail shaft down in the stem tube 1^ inches. The machinery 

 was located aft, with one section of the line shaft between the tail shaft and the gear, the 

 turbines being located aft of the gear, so as to permit of drawing the tail shaft. No dam- 

 age was done to the gears. 



