ELECTRIC PROPULSION OF THE U. S. S. JUPITER. 195 



eral large vessels will, within a short time, be contracted for. If such a beginning 

 can be made, the practical results accomplished will soon develop great activities. 



DISCUSSION. 



The Chairman : — Will you show on the blackboard what you mean by the efficiency 

 being 68 per cent and 74 per cent. Those are terms not commonly used. 



Mr. Emmet: — I am referring to the Rankin efficiency; that is, a comparison with the 

 performance of the perfect steam engine. 



The Chairman : — The actual efficiency of the turbine, as compared with the efficiency 

 of the perfect primary engine, is 74 per cent? 



Mr. Emmet: — Witliin that particular range of steam operation. 



The Chairman : — I thought that was what you meant, and wanted to have it under- 

 stood. It does not mean the thermal efficiency 



Mr. Frederick P. Palen^ Member: — I wish to ask Mr. Emmet one question, which 

 is probably so easily answered, he has not considered it necessary to mention it. However, 

 it is not clear to my mind exactly how the power is balanced between the generators and 

 motors in cases where the propellers are reversed, slowed down or start up. Is that done 

 electrically, or do the loads balance from the action of the governors? 



Mr. Emmet: — -Variations of speed in the Jupiter are accomplished by variations of the 

 steam admission, as in any other ship. The electric generator and motors simply act as a 

 speed-reducing bond between the turbine and the propellers. Reversal is accomplished by 

 changing the electrical connections so that the generator tends to drive the motors in the oppo- 

 site direction. After reversing, the motor very rapidly assumes a speed in the opposite direc- 

 tion in proportion to that of the generator, and this speed can be varied by the steam admis- 

 sion. On the Jupiter turbine a governor is used which can be set to hold any desired speed, 

 but this governor simply affords means of maintaining and varying the steam admission as 

 desired. 



Naval Constructor Joseph H. Linnard, Member of Council: — I ask Mr. Emmett if 

 among the few experiments that were made, under the circumstances he mentions on the 

 Jupiter, there was any experimentation on the subject of quickly reversing at full speed, 

 when the vessel is full speed ahead, reversing quickly and going astern. It is known that 

 brings very heavy strains on apparatus of any kind in propelling a ship, and is a pretty se- 

 vere test of any machinery. 



