Transportation on Water 



367 



turbines receive the used steam from the exhaust of the engines, 

 and furnish about as much power as do the reciprocating engines 

 before discharging it into the condensers. It involves no in- 

 crease in fuel consumption. This, like the use of water power, 

 illustrates the advance 

 in power development in 

 the last few years. 



Defects of the turbine. 

 In the use of the 



, . ,, Moving J3lades 



steam turbine there are 

 at present serious diffi- 

 culties, one of which is 

 the impossibility of re- 

 versing it. A modern 

 steamship equipped only 

 with turbines has four 



Stationary Blades 

 Moving Blades 



Stationary Blades 

 Moving Blades 

 turbines for driving the FIG. 131. Diagram of steam turbine, showing 



ship ahead, and two for course of steam ' 



driving it astern. When reversal is necessary, the steam is shut 

 off from the four turbines and supplied to the two propelling 

 the ship backwards. 



Several methods of solving the difficulty have been attempted. 

 One is to equip the steel shafts of the turbines with electric 

 generators and to utilize the electricity in driving the propellers. 

 The high speed, the invariable output of power, the depend- 

 ability, and efficiency of the steam turbine make it ideal for 

 driving electric generators. Reversal of electric motors does 

 not interrupt the work of the turbines. Another method is to 

 have the steam turbines operate a water pump which in turn 

 operates water turbines that drive the propellers. The water 

 is used repeatedly until it becomes hot through friction, when 

 it is turned into the boilers, and an equivalent amount of cold 

 water supplied automatically. This method is highly efficient, 

 yielding about 90 per cent, or a loss of about 10 per cent, of 

 the power developed by the steam turbine. 



