. An elementary book on electricity and magnetism and their applications. ently been of interest to marineas well as to electrical engineers is that of electric ship propul-sion. For many years our large ships have been propelledby multiple-expansion reciprocating steam engines, and thenmore recently by steam turbines. But it has been found thatthe steam turbine works at its highest efficiency when at fullspeed, which is much higher than the desirable speed for pro-pellers. Then, too, the turbine is not itself a reversible ma-chine, which necessitates small turbines for astern work. Toget rid
. An elementary book on electricity and magnetism and their applications. ently been of interest to marineas well as to electrical engineers is that of electric ship propul-sion. For many years our large ships have been propelledby multiple-expansion reciprocating steam engines, and thenmore recently by steam turbines. But it has been found thatthe steam turbine works at its highest efficiency when at fullspeed, which is much higher than the desirable speed for pro-pellers. Then, too, the turbine is not itself a reversible ma-chine, which necessitates small turbines for astern work. Toget rid of these two difficulties there have been suggested twosolutions. One is to use high-speed turbines connected bymechanical gearing of the double helical type (Fig. 367). Bythe use of suitable gearing the turbine and propeller may bedesigned for the speeds at which each works most advanta-geously. For example, a 4000-horse-power turbine running a11250 drives a propeller shaft at 130 through a gearand pinion of the double-helical type. This gearing has been. Fig. 367. — Double helical gears for reducing speed of two steam turbines(right) and transmitting 3000 h. p. to propeller shaft (left). ELECTRIC TRACTION 515 so designed in its case as to give an elastic support for thepinion shaft in a floating frame, which is carried on hydraulicrams. This support renders the gearing practically noiselessand insures nearly perfect alignment between gear and pinionunder all conditions. The transmission efficiency of reductiongearing may exceed 98 per cent. The other plan is to use between the prime mover and thepropeller electrical transmission (Fig. 368). In this methodthe propeller is driven by an electric motor mounted directly
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
