18 REDUCTION GEARS FOR SHIP PROPULSION. 



or vibration, and on inspection it was found that both bearings and teeth had altered so much 

 that it was necessary to regrind the bearings and recut the teeth. This would seem to show 

 that when first made there were stresses in the material which annealing had failed to re- 

 move or which had been left by the heat treatment. It is suggested that it would be advisable 

 to make casings, wheels and pinions ahead of time and allow them to stand out in the weather 

 so as to get rid of these internal stresses, before machining. 



Considerable difference has been found in the hfe of gears of the same design, between 

 those fitted amidships and those fitted in the stem of the ship, the latter wearing more 

 rapidly. The inertia of the turbine is much grieater than that of the propeller and shafting, 

 and the turbine will run with practically uniform angular velocity while the motion of the 

 propeller will be uneven due to the different conditions of water, depths, etc. This variation 

 will have little effect on the gears when transferred through the long, flexible shaft of the 

 machinery fitted amidships, but with the short shaft for those fitted in the stem of the vessel 

 this variation of torque will be reflected on the teeth without any damping due to the shaft. 

 When reduction machinery is fitted in the after end of the ship it is better to fit the turbines 

 aft of the gears so as to make the line shaft as long as possible. 



A number of gears have been fitted with a flexible shaft between the turbine and pinion 

 or between the high-speed wheel and second-speed pinion. This device was patented by Mr. 

 Day of the Falk Company for use on reduction gears where the torque from a single pinion 

 has to be delivered through two wheels and pinions to a single wheel. The device is illus- 

 trated on Fig. 10, Plate 5. The pinions are made hollow and a flexible shaft passes through 

 the center and is made just large enough to carry the load safely. It is attached to a turbine 

 or high-speed wheel by a solid coupling and to the after end of the pinion by means of an 

 extensible pin coupling. The weight of the shaft is taken in an easy fitting bearing at the 

 end of the pinion. These torsion shafts are admirably placed for taking up the variation be- 

 tween the propeller speed and that of the turbines and eliminate to a great extent the tur- 

 bine vibration being communicated to the gears. 



The superheater has, so far, not found much favor in America for marine purposes, and 

 considering the number of turbine-driven vessels that are being built it is surprising that 

 so many are working without superheat. The turbine under the same steam conditions 

 gives an efficiency of 10 to 15 per cent better than the reciprocating engine. From the actual 

 service results of three steamers of the same capacity and in the same trade and running 

 55,000 miles a year, the one with triple-expansion engines used 335.3 pounds of oil per knot 

 and the other two with turbine machinery used 281.5 pounds and 282.5 pounds of oil respec- 

 tively. This could have been improved considerably by the use of superheat with very little 

 increase in the cost of the turbines. Practically all that would have been needed would be to 

 make the high-pressure end of the casing of cast steel instead of cast iron. 



There is shown in Table I a comparison of machinery for 20,000 deadweight tons com- 

 bined ore and oil vessels, showing the relation as to the weight, space, cost and operating 

 expense for reciprocating engines, turbines and reduction gears, Diesel and electric drive 

 on these particular vessels. In this the Diesel engine is rather at a disadvantage owing 

 to the necessity of fitting considerable boiler power for heating the cargo oil. All the sets 

 are twin screw. 



