76 ENGINEERING PROGRESS IN THE U. S. NAVY. 



can make it very much better, and the aim of Sir Charles Parsons and others who 

 have worked intelligently on the problem of gearing turbines to ships' propellers 

 has been in the direction of a moderate speed reduction, making possible a good 

 turbine, and at the same time retaining a fairly good propeller speed. I have 

 nothing to say against this. I have experimented successfully on gearing a good 

 deal myself, and I think that it is a very hopeful thing, but until we can have big 

 enough ratios of speed reduction, it is not justified as compared with electricity, 

 because the electrical equipment is extremely simple, extremely light, and has a high 

 eJEciency, which is perfectly well known and which is absolutely unquestionable. 



The efficiency of reduction in the apparatus on the Jupiter is 92 per cent, that 

 is, there is 8 per cent loss in electrical apparatus. Now if you study the curves of 

 propeller performance you will see that small concessions in the matter of propeller 

 speed cannot be made without losing more than that. From such data as I have 

 been able to obtain concerning gearing, I do not see how a ship like the Jupiter 

 could be properly propelled, with proper propeller speed and turbine speed, unless 

 you use double reduction, and double reduction is a complication. Therefore 

 my plea for electrical propulsion is that it gives us the rate of speed we want, some- 

 thing we know about, and we do not have to look into the future at all for our data. 

 I simply say that the propulsion of ships by the methods now used is absolutely not 

 justified in the light of the performance the Jupiter's machinery has made, the means 

 of speed reduction being thoroughly well known. 



The electrical propulsion designs which I have made, and which have been 

 published in papers which I have read, show certain equipments which the develop- 

 ments of recent times has enabled us to considerably simplify, so that the electrical 

 part is simpler than it was when I wrote those papers. Such means have been in 

 part devised in connection with the driving of locomotives where we need a very 

 high torque in securing the necessary starting power. In running electric loco- 

 motives a method of designing alternating current motors has been developed 

 which has a characteristic, by the use of induction in the rotor, making the rotor 

 so that it will give a high torque only when out of synchronism with the generator 

 and will give good efficiency when it is in synchronism. This gives us the quality 

 which we need in ship propulsion. This rotor is so constructed that its windings 

 present a high resistance to currents of high frequency and a very low resistance 

 to currents of low frequency. When a motor of this type is at a speed nearly 

 synchronous with the generator the effective resistance of rotor winding is low 

 and the motor is virtually as efficient as a motor of the ordinary type designed 

 for small full load slip. When the motor departs from the nearly synchronous 

 condition, as in the act of reversing, the self-induction of the rotor winding causes 

 the bulk of the current to change its path, and to act through channels of high 

 resistance, so that a high torque is maintained, as would be the case if a consider- 

 able resistance were actually switched into the rotor circuit. 



By that method we can use a motor without external resistance, and this 

 constitutes a very great simplificaton, because there are no connections to be 

 changed, and the ship can be operated by simply throwing switches without inter- 



