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Steam Turbine (Continued from Page 12) auxiliary machinery driven from the niain engines by suitable gearing and with suitable standbys. The inclu- sion of the last was made at the suggestion of the late Sir Charles Parsons and reference to it is per- laps not without interest in connec- tion with what follows later in the present paper. The progress in economy above al- luced to has pervaded all classes of ocean going vessels and in particu- lar that class which is the subject of the present paper. The time honored triple or quadruple expansion engine which has held the field almost ex- ciusively for this class of steamer in the past has proved powerless un- assisted to maintain its position in this respect, wherefore many pro- posals have been made and actually earried into construction to attain increased economy by the addition to the reciprocating engine of a low pressure turbine, the power of which is utilized in various ways to aug- ment the total output. Regarding this as a means of increasing the output cr reducing the consumption of an existing reciprocating engine, opin- ions still differ as to whecher the in- c1eased output or increased economy so obtained justifies the additional cost incurred, and it is easy to un- derstand that the answer to this question will vary with the circum- stances in each individual case. Such plants however do not stand in the front rank of economical perform- ance. A complete installation of geared turbines gives a_ greater economy of steam and fuel, even at ordinary pressures, while at high pressures and temperatures still bet- ter results are being realized. It should be recognized, therefore, that the field of such combined installa- tions is in reality limited to the cases where a reciprocating engine is al- ready existing or predetermined by force of other circumstances as a pert of the unit. A Simplified Propelling Unit In expectation of a revival of de- mand for cargo tonnage in the near filture a new type of design of tur- bines and gearing has been specially developed by the firm with which the author is associated, for cargo boats of small power, such as tramp steam- ers of from 1500 to 2000. shaft horsepower particularly with a view to standardization and simplicity of erection, providing a simple, cheap and reliable plant of the power re- quired with a minimum of component parts and a minimum of assembly, connecting-up or alignment to be done when erecting the installation in the vessel. The author owes an acknowledg- ment here to J. Johnson, since it was in collaboration with him that the 38 conception arose of developing a simple unit of this character which would secure the acceptance of tramp shipowners, their superintendents and engineers. The installation de- signed with these principal objects ini view has been called the ‘‘Simplex unit.” The mechanical reductiou gearing consists of a single train of gear wheels in simple succession, a single high speed pinion driving a primary wheel, and a secondary pin- ion on the same shaft as the primary wheel driving the main wheel on the propeller shaft. It will be seen that this unit dif- fers in an important respect from the usual turbine drive in which there are two or more pinions, trans- mitting power to the gearing at the sume time, and in which a higher de- gree of accuracy is necessary, since the inertia of the turbines tends to maintain the speed of the separate pinions in constant relation. The two turbines of the Simplex unit are ar- ranged to drive this single pinion. They consist of a high pressure tur- bine, with ahead and astern portions, eoupled at the after end of the primary pinion, and a low pressure turbine, also with ahead and astern portions, coupled at the forward end of the same pinion. Another feature in the gearing is that the teeth are of the single helical type. This en- sures a smooth and positive drive in tuat there is no fore and aft motion of any of the gears. Mounted on Gear Case The turbines and condenser are mounted on the g2ar case. The main thrust block is also incorporated in the gear case, so that the attach- ment of the whole assembiy to the ship is made only through the gear ease feet, and a single operation of alignment is sufficient for this as- sembly. Further the alignment of turbines and gearing is not disturbed by any straining of the ship, The end thrust of the teeth of the main wheel is in opposition to the thrust of the propeller, reducing, therefore, the load on the main thrust block. The intermediate shaft and the primary pinion have each its own thrust block to take up the end thrust of the teeth. The pinion and each of the turbines runs in its own bear- ings, but the pinion shaft is con- nected to the turbine shaft on each side of it by an expansion coupling instead of rigidly, so as to avoid any accidental bending stresses occurring in the event of any difficulty in main- taining the six bearings accurately in line. A unit of this description has been built at Turbinia works for a total output of 2000 to 2250 shaft horse- power at a propeller speed of 80 revolutions per minute. After erec- tion it has been subjected to exhaus- tive tests at full power, the power being absorbed and measured by a Froude dynamometer, MARINE REVIEW—March, 1935 Steam is supplied to the turbines from the works’ high pressure boiler at a pressure of 270 pounds per square inch and superheated to 750 degrees Fahr. The exhaust steam is condensed in the condenser, which is part of the unit, at a vacuum of 28% inches to 29 inches. Tested un- der these conditions at full power oi 2000 shaft horsepower, the steam consumption is about 8% pounds. The economy of steam consumption is well maintained even at half power. A special auxiliary unit to which reference will presently be made has been designed to go with this set of raain machinery, and it is intended tc erect and test the whole installa- tion in the works as a self contained unit. Moderate Steam Pressure A moderate steam pressure has been adopted in order that any type of boiler can be used in conjunction with this machinery. A general lay- out has been made for a steamer of 8500 tons deadweight, with boilers of the Howden-Johnson type de- signed by The Wallsend Slipway & E1igineering Co. Ltd., adapted for both coal and oil burning. With pre- heated air in the heaters it is esti- mated to obtain a boiler efficiency of 80 per cent and this is in conjunc- tion with the steam consumption above mentioned and a suitable al- lowance for driving the auxiliaries should give an overall consumption under 1 pound coal per indicated horsepower. The total weight of ma- chinery is 140 tons less than for a similar outfit with reciprocating en- gines. A still more compact arrangement of geared turbines on somewhat simi- lar lines will also be of interest. In this design there are two primary pinions driven by high pressure and low pressure turbines respectively and one secondary, the turbines be- ing mounted on the condenser at the forward side of the gear case. The main propelling unit being simplified in the manner described, it was natural to inquire into the possibility of making a similar sim- plification for the auxiliary pumps and fans. For this purpose it is desir- able to consider how far it is possible to reduce (1) the number of units to be installed, (2) the number of in- dependent operations required for their control, and (3) their steam consumption, or in other words the cost of driving them. It is an attrac- tive proposal, and one which has often been made, to drive all the auxiliary plant by gearing or other- wise from the main engine. Another equally attractive suggestion that has been advanced is the grouping of the various auxiliary units to- gether in order to drive them all from a single engine with a system of countershafts and pulleys ana- (Continued on Page 40)