280 ELECTRIC PROPULSION OF MERCHANT SHIPS. 



cessful in many warships, but these are subject to only occasional short periods of 

 high-power service. In some merchant ships gears have been very successful, and 

 in others most serious trouble has been encountered. Variations of results in simi- 

 lar equipments in different ships illustrate some of the possible uncertainties. Par- 

 sons' original gear applications operated with a single reduction, very small diame- 

 ter pinions, and a large diameter gear on propeller shaft. Some of these have 

 been reported to be very successful, but the gains in economy shown in Parsons' pub- 

 lications are nothing like so great as those accomplished by high-speed turbines with 

 double reduction gears. There have, however, been many cases of failure with 

 gears of this type. In fact there seems to be no type of gearing with which trouble 

 has not been experienced after long service in cargo vessels. 



Recent production of so-called "Standard English ships" shows they are being 

 equipped with double-reduction gearing, and at the same time that this change of 

 method is being adopted in England the use of single reduction is being extensively 

 advocated and applied here. Although all the original American equipments in mer- 

 chant ships were double reduction, the writer has seen a solid-gear, double-reduction 

 equipment of American make in which the gears were badly worn and pitted after 

 17,000 miles of service, and in this case the proportions of gears are closely equiva- 

 lent to those which have been adopted in the new standard English ships, and the 

 conditions of design and manufacture quite as good. 



These indisputable facts and many others certainly indicate that gearing for 

 ships has not yet reached a state of finished development. 



One of the uncertainties of gear operation in ships is illustrated by the very 

 great difference in durability of gears in ship propulsion and in shore uses. In 

 trials on shore, gears have borne without blemish, for equal periods, loads equiv- 

 alent to approximately four times the average loads which have caused bad de- 

 struction of similar gears at sea. This is illustrated by the photograph shown in 

 Plate 119, and the data there given are characteristic of many other similar experi- 

 ences which have developed. 



The reasons for these astonishing differences have never been adequately ex- 

 plained. Plate 120 shows a record taken from a torsion coupling on a cargo vessel 

 operating in ballast in a moderate seaway. This record shows that the torque on pro- 

 peller shaft varied from zero to approximately 75 per cent overload under certain 

 wave conditions. The effect of bad weather on endurance of gears has often been 

 observed, and it is quite possible that variations much greater than that here shown 

 may at times be experienced. In this case the ship was pitching only 4 degrees. 

 Part of the small, quick variations shown in this record were caused by a transmit- 

 ting ring which ran slightly out of true in the instrument, but otherwise the con- 

 ditions were such that the record must be substantially correct. 



Another matter of uncertainty in geared-turbine equipments is the matter of 

 temperature in turbines. The operation of turbines in the reverse direction occa- 

 sions large temperature variations, and temperature variations constitute a fruitful 



