194 THE APPLICABILITY OF ELECTRICAL PROPULSION TO 



so as to put in the resistances ; third, close the "astern" or "ahead" switches as de- 

 sired. The total time required for these operations is about three seconds. When 

 the installation was first designed, the solenoid locks in the generator field circuit 

 were so arranged as to prevent the short-circuiting levers being moved either to cut 

 out or cut in the resistances, but it was found that, with the motors dead (that is, 

 with no oil switches closed), the short-circuiting levers could be moved with im- 

 punity, so that notches in the lock were filed to allow the short-circuiting levers to 

 be moved to the "resistance in" position without changing the field of the generator. 

 This was a great improvement as it made it possible to give practically instantane- 

 ous backing at all times and under all conditions. 



In connection with the operation of machinery there are several other condi- 

 tions that might possibly arise in addition to the normal condition given. The rhe- 

 ostats might become disabled, in which case the mechanical interlock between short- 

 circuiting levers and the oil switches would be disconnected, making it possible to 

 move the oil switches with the rheostats cut out. The ship could then be maneu- 

 vered satisfactorily, but it would always be necessary to slow the ship down before 

 backing the motors. This condition has been tried out experimentally, and it was 

 found that up to speeds of about 9 knots the operation was just as satisfactory 

 for starting up and backing with the resistances out as it was with them in. Above 

 that speed it was necessary to wait until the ship slowed down. 



If either motor were disabled, the ship could, of course, be propelled with, the 

 other. 



In case of failure of the governor, the speed could readily be controlled by the 

 throttle itself. 



In case of damage to one or more stages of the turbine, the blading of these 

 stages could be entirely removed or simply opened up enough to allow the passage 

 of steam through them, and the turbine operated. 



The General Electric Company, in its contract with the government, guaran- 

 teed a water-rate of 15 pounds of water per shaft horse-power hour delivered to the 

 propeller shafts at ten knots, and a water-rate of 13 pounds of water per shaft 

 horse-power hour delivered to the propeller shafts at the highest speeds attainable. 

 The government guaranteed to furnish steam to the turbine at 190 pounds (gauge), 

 or to allow an increase of one per cent per specified horse-power for each 10 pounds 

 of reduction in steam pressure. It also guaranteed to furnish 28.5 inches of 

 vacuum or to allow an increase in the water-rate of 5.0 per cent per specified 

 horse-power per inch of reduction in vacuum. The results of the preliminary trial 

 are given in the following table : — 



