REDUCTION GEARS FOR SHIP PROPULSION. 15 



the good and bad of design or material, but this is a condition which is rapidly improving and 

 there are now plenty of engineers experienced in the handling of turbines and gearing. 



The lubricating oil systems of most of the later boats have been standardized on the 

 lines set forth in a paper by Messrs. Smeltzer and Fernald, read before the Society in No- 

 vember, 1919. 



The gravity system insures a constant pressure of oil to all parts of the engine, and 

 the increased capacity of drain and gravity tanks allows for a slower circulation of the oil 

 and provides a reserve supply which will last a few minutes after the pumps stop and allows 

 the turbine to be safely shut down. The settling arrangements are greatly improved and the 

 use of the DeLaval separator will do much to improve the condition of the lubricating oil. 



There is still frequently encountered the misconception in regard to lubrication that the 

 lower the temperature of the oil fed to the machine, the better will be the lubrication. The 

 gears would, of course, run better with cool oil or oil of high viscosity, providing it is not too 

 cold to reach the wheels from the spraying nozzles, but bearings require oil of low viscosity, 

 and as it would be cumbersome to have two oiling systems it is necessary to compromise be- 

 tween these two, and it has been found from experience that, with oil of 500 seconds 

 Saybolt viscosity, good results are obtained on both gears and bearings when the inlet oil 

 temperature is between 100° and 110° F., that is to say oil at a viscosity of about 450 secondg 

 Saybolt. Bearings fed with oil of low temperature are found to generate more heat and 

 wear rapidly, whereas with oil of proper viscosity the wear, over considerable periods, is 

 practically negligible. 



Accuracy in the cutting of the teeth and machining casings, assembling and setting 

 up of parts is absolutely essential for insurance of good running. The clearance in the 

 bearings must also be uniform so that in whatever direction the pressure is to be taken 

 they will maintain the pinions in a true line with the wheels. The casing should be made as 

 stiff as possible and will be better if it is so designed that it is rigid enough to hold its form 

 when placed on the ship seatings for the process of fitting the packing blocks. The two- 

 plane and three-plane types are specially advantageous in these respects as the depth is so 

 great as compared with the area covered by the gear. Ship seatings should also be de- 

 signed so that they will add to the stiffness of the casings. A ship is generally quite flexible 

 and alters considerably with change of trim and works due to the action of the sea. It seems, 

 therefore, desirable to make the seatings so that they will not be influenced by the movements 

 of the ship, that is to say, they shall be substantial structures set down on the ship's bot- 

 tom and free of all connections to the ship's side or bulkheads which would have the effect 

 of transferring to the gears the movements of the ship. They should be arranged to main- 

 tain the aligrmient of the gears and turbines, and not, as is so often the case, to add strength 

 to the ship's structure. 



The maintenance of the contact of the pinions and wheels along the whole face is a 

 matter of one or two thousandths of an inch and unless this alignment is strictly main- 

 tained it means that the work has to be done by only a part of the face and that the part 

 which actually does the work is subject to increased pressure. 



Undoubtedly some gears have been manufactured with tooth pressures greater than 

 present day materials and manufacture will stand. Devices for giving flexibility and 

 to compensate for misalignment have been tried out in the test house and have shown 

 the capacity of gearing to work under loads far in excess of those used in service. These 

 tests would be carried out under the best conditions with little to distort the casings or to 



