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Improved Reduction Gears Have Extended the Use of Turbines as a Means of Ship Propulsion—Description of Herringbone Gear HE steam turbine has many ; desirable features which have led to its adoption for numer- ous phases of power application on both land and sea. The most promi- nent features are the economy of floor space, the absence of vibration, the simplicity of operation and the low cost of upkeep. Economy of operation is secured in part by the ability of the turbine to run under a high vacuum; it also is pos- sible to secure an oil-free condensate for the boilers. All of these advan- tages are believed to apply with equal force to steam-turbine installations for marine service, but until recently the steam turbine has been used prin- cipally in high speed vessels, usually of large size, and in most cases the turbines were directly connected to the propeller shaft. Owing to the difference between the turbine speed necessary for the highest efficiency and the proper pro- peller speed, direct connection of steam turbines to propellers requires a compromise speed which is_ not suitable for either the turbine or the propeller. For low speed cargo-carrying boats, where the propeller speed in most cases does not exceed 125 revolutions per minute, it is obvious that direct connection of the turbines to the pro- peller would be impracticable. The HERRINGBONE REDUCTION GEARS, WITH COVER REMOVED logical solution, therefore, is to in- terpose speed reducing gears between the turbine and the propeller, which will permit both the turbine and the propeller to run at their most efficient speeds. The interpolation of reduc- tion gears greatly reduces the weight and size of the turbine. Flexibility in Turbine Applications Flexibility of design is also possible, depending on the requirements of the installation, it being possible to de- sign the turbine for moderate ca- pacities in either one or two casings per propeller. By installing two tur- bines, one high pressure and the other low pressure, each provided with its own pinion operating on the gear connected to the propeller, a substan- tial duplication of driving machinery is obtained,. since either half of the turbine can be operated independently on boiler steam, if this is so desired. The De Laval Steam Turbine Co., Trenton, N. J., which has been en- gaged for some years, in the develop- ment of high. speed, double-helical, speed-reducing gears for steam ‘tur- bine service, is building a number of large gear reduction sets for marine service. One outfit under construc- tion consists of two 2,500 horsepower reduction gears to be installed in a twin-screw freighter. Each unit con- sists of two pinions operating at 2,200 revolutions per minute on one gear running at 110 revolutions per min- ute. The De Laval company also is supplying the gears for two 17%- knot, 10,000-ton, passenger boats, each screw requiring 4,500 _ horse- power. The gear reduction for each propeller consists of two pinions operating on a main gear, the pin- ions running at 1,500 revolutions per minute and the gear and propeller at 120 revolutions per minute. For each reduction, one pinion is operated by a high-pressure turbine and the sec- ond pinion by a low-pressure turbine. An essential feature of these re- duction gears is the use of gears and pinions rigidly supported in the casing. This construction is advis- able, as any resiliency or flexibility between gear and pinion results in unequal pressure and wear, and the most effective means of _ insuring TURBO-DRIVEN GENERATOR 279