All About Engines

Engines for Ships 3°3 ing engines to the condensers. The inside of this turbine contains as much space as the room of many a cottage, and if a dining-table were placed down the middle a dozen persons could sit down to a meal without feeling cramped ! The second of the newer methods of propulsion is to use steam turbines and to transmit the motion to the propeller shaft by means of gearing. Ordinary toothed wheels are very noisy, and the more noisy they are the worse they wear. Even with the most accurate gearing for large powers and high speeds, as ordinarily made, there are inaccuracies of sufficient magnitude to cause knocking and grinding. But Sir Charles Parsons showed that these inaccu- racies were due mainly to inaccuracies in the machine in which the teeth were cut, that they occurred at regular intervals, and that by an alteration in the design of the machine they could be spread out all round the wheel—spread so thinly, in fact, that they became practically indistinguishable. The gearing then ran silently and with so little friction that it transmitted 98J per cent, of the power from one shaft to the other. Moreover, it enables a turbine to run at high speed with the highest efficiency, and the propeller to run at low speed with the highest efficiency. The geared turbine, as the above arrangement is called, has received a great impetus by the in- vention of the Mitchel Thrust Block. When the screw rotates it pushes the water backwards from the ship’s stern, while the reaction tends to force the