60 



THE WORLD'S ADVANCE 



stance, while the turbine operates at its 

 highest efficiency when driven at a very 

 high rate of speed, the screw propeller 

 of the ship attains its maximum efficiency 

 when turning at a speed approximating 

 one hundred revolutions per minute. This 

 means the introduction of gearing or 

 some other mechanism to reduce the 

 speed of the turbine to that best adapted 

 to the propeller. Added to the cost of 

 this mechanism is its liability to damage, 

 for the transmission of several thousand 

 horsepower of mechanical energy is no 

 small problem to contend with. Further- 

 more, the steam turbine runs inherently 

 in one direction only. If it be made re- 

 versible, the rotor must be in duplicate, 

 which means that not only must the 

 working rotor drive the propeller but it 

 must also carry around the idle rotor. 

 The only other alternative is in the in- 

 stallation of a second set of turbines for 

 backing purposes only and the tremen- 

 dous cost of this system is obvious. Flex- 

 ibility of control in both backward and 

 forward movements is of the highest im- 

 portance in the fighting ship and for this 

 reason the builders have been forced to 

 employ a driving mechanism embodying 

 every possible feature of advantage re- 

 gardless of the cost of installation and 

 subsequent operation. 



Another essential in the propulsion of 

 a battleship is that it shall be capable 

 of cruising day in and day out at a 



speed of some fifteen knots per hour and 

 at the same time be able to make a 

 sudden, though perhaps long-continued, 

 spurt at its maximum speed of twenty- 

 two knots. The turbine is essentially a 

 one-speed machine. As remarked be- 

 fore, its ideal operating speed is a high 

 one. In order, therefore, that it be made 

 capable of attaining the higher speed, it 

 must be operated for the greater part of 

 the time i. e., while cruising, at com- 

 paratively low efficiency. 



The great flexibility of control found 

 in the electric motor admirably adapts 

 it to the purposes of ship propulsion. 

 The speed, moreover, is in accordance 

 with that at which the propeller should 

 be driven. Granting this, the problem 

 has been to so combine the motor with 

 a generating unit that the very utmost 

 of efficiency could be realized at all times 

 and under all conditions from each indi- 

 vidual unit of the entire plant. Appar- 

 ently this result has been secured in the 

 system under our consideration. The 

 original installation of the kind was 

 placed in the U. S. collier Jupiter some 

 two years ago and during the interim 

 there is not a single case of electrical 

 trouble on record although the ship has 

 been in practically constant and trying 

 service. 



An examination of the simple diagram 

 which is reproduced on this page will 

 serve to make clear the plan of the 



Two turbo-generators, operating either independently or in tandem, supply the current which 

 operates the electric motors that drive the propellers. 



