16 REDUCTION GEARS FOR SHIP PROPULSION. 



upset the alignment. The conditions at sea, however, are entirely different and it is diffi- 

 cult to estimate what may have to be taken into account. Apart from the alteration in a 

 ship's structure due to loading or trim and running light there is the occasional disturbance 

 due to heavy weather, the effect of which cannot be calculated. With the reciprocating en- 

 gine the results are apparent and it is necessary to ease down and stand by, but with the 

 turbines and reduction gears considerable variations may take place in the revolutions with- 

 out making themselves felt except by a change in the hum of the engine. The constant 

 change in inertia has all to be taken up by the teeth and it has been noted that gears which 

 are heavily loaded wear rapidly in stormy weather. 



The tables (Plate 4) show the principal dimensions of gears by different makers. Fig. 

 1 for double reduction gears and Fig. 2 for single reduction. These are by no means 

 complete but are representative of what has so far been made. Plate 5 shows diagrammati- 

 cally the arrangement of wheels and pinions for a variety of reduction gears and is explan- 

 atory of some of the terms used in the paper. 



The single reduction sets are generally satisfactory and out of the large number fitted 

 there have been very few failures. The tooth pressures are not excessive ; those for war ves- 

 sels may be fairly high, but they have only to work at full power occasionally and for very 

 short periods. The turbine speeds are usually moderate and the inertia of the moving parts 

 correspondingly low. It is easy to estimate the load on each pinion due to the turbine, and 

 the difference between mean and maximum torque is much smaller than in the case of double 

 reductions with their high-speed turbines. In the latter (Figs. 4 and 5, Plate 5), where a 

 single turbine is used to drive two sets of wheels and pinions, it is difficult to assemble them 

 so that work is divided evenly between the two sets, and any uneven wear or adjustment of 

 the bearings will throw most of the load on one side or the other with an increase of the tooth 

 pressure on that side. 



Some of these gears are also solidly coupled together so that there is no give in the 

 gears themselves to compensate for this uneven loading. 



The single reduction gears under column 9, Fig. 2, Plate 4, have given considerable 

 service. They were installed on the Orizaba and Sibboney and were manufactured by the 

 DeLaval Company. Both of these vessels were operated under very severe overload con- 

 ditions during the war. The Orizaba has steamed, to date, over 225,000 miles and the Sib- 

 boney 175,000 miles. It is stated that when the gears were last examined they were in excel- 

 lent condition. All the other gears of this sort, tabulated, are, so far as can be learned, 

 operating well, though the mileage is much less than in the case of the two ships quoted. 



Amongst the double reduction gears there are some cases of extended running which 

 point to the loads which gearing will stand safely. The S. S. Pacific in service since Decem- 

 ber, 1915, still has the original low-speed gears, which, on last report, had made 240,000 

 miles. The S. S. Sucrosa in service since July, 1916, also has the original low-speed gears 

 after running 225,000 miles. The high-speed train was renewed after 120,000 miles. The 

 S. S. Mielero had the original gears still in use after three years running during which she 

 made 160,000 miles. These are all of the two-plane type (Fig. 5, Plate 5) and were made 

 by the General Electric Company. 



The design tabulated in column 1, Fig. 1, Plate 4, has given an excellent account of 

 itself and there have been no break-downs or repairs. Some of these units have been in service 

 over two years and show little sign of wear. Those tabulated under column 3, Fig. 1, Plate 

 4, have also given excellent service. Both of these are Falk gears. 



