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bine geared generators rather than by diesel driven sets, owing to the greater freedom from vibration and noise. With such an installation, four turbine generators will be installed, each of 45,000 shaft horsepower maximum and four synchronous-in- duction motors, one for each propel- ler shaft operating at 174 revolu- tions per minute maximum. The generators will be three-phase, about 75 cycles, 6000 volts. To avoid ex- cessive lengths of steam piping and for trim and increased safety the tur- bine generators will be installed in two engine rooms with one group of boilers forward of the forward en- gine room and the second group aft of the after engine room. With four generators and four motors there are several combina- tions of inter-connection possible. Only eight are considered necessary to provide sufficient flexbility for emergency or reduced power opera- tion. Four of these combinations would be, each generator supplying all the four motors. Under certain conditions one complete engine room could be shut down, and with the two propulsion generators in the other engine room, at least 75 per cent speed attained with efficient operation. Governors for Speed Control The speed of the propulsion mo- tors is varied by changing the turbine speed setting through hydraulically operated governors manipulated from the central control station. An auxiliary machinery room will be located common to the two en- gine rooms. The propulsion motor rooms will be located aft of the after boiler room, the two outboard motors for- ward and the two inboard motors somewhat aft. Each pair of motors will be in separate watertight com- partments. Auxiliary machinery will be gen- erally electrically operated, current for which will be supplied by auxil- iary alternating current generators. Excitaton for the propulsion gen- erators and synchronous motors will be provided by three turbine driven, double unit (2 x 400 kilowatts) di- rect current generators, one for each engine room with the third as a spare. Keeping Motors in Step To prevent the motors from pulling out of step with the generators in case of rough weather or unusual turning, the propulsion machinery will be liberally designed to provide a motor torque margin of not less than 30 per cent at 45,000 shaft horse- power per motor.” The propulsion generators will have the closed circuit system of ven- tilation provided by surface air cool- ers and internal fans on the rotors. This reduces the noise and aids in keeping the clean. For the propulsion motors external motor driven blowers will be fitted to exhaust air from the motors and dis- charge it through surface air coolers into the motor room, for again cir- culating through the main motors, the motor being closed. Control of the main propulsion ma- chinery will be from a central sta- tion located where most convenient for cable leads and where best pro- tected from possible damage by col- lision. With central control, the en- gineer in charge has a contact with the machinery which cannot be ob- tained with any non-electric propul- sion system. By means of the instruments on the control panel, the engineer can measure the actual power delivered to the propellers, momentarily or for any part of the voyage or for the en- tire trip. This information will as- sist in the accurate calculation for fuel consumption, in observing the division of load between the different generator windings included in air heater boxes, uptakes, additional ducts and greater fan ca- pacity required. The engineer crew would be increased, top side weights would be more, and the machinery would be somewhat modified. The heater boxes would encroach on the lower deck area to the extent of 3000 to 4000 square feet, thus reducing valuable pay deck space. The air pressure would be increased and there would be more burners re- quired. Any operating company be- fore building a large liner would go carefully into the merits of a simple installation as compared with a more intricate one. Simpler System Advantageous The authors believe that at the present time the overall advantages of the simpler system with the less pressure and temperatures are to be recommended. Instead of particular- ly stressing making this the most economical ship as regards fuel con- sumption, the authors are considering the problem from a standpoint of the Data S.S. President Hoover and Coolidge Table 3 Hoover Coolidge Mean: displacement: tons 2225. 355. 6s FO Se ee 24,330 22,927 otal SF Pos ie hc a ee ee ee 26,495 27,089 Propellercrsp. me es ee aie ee Oe a a oe Oa 4.4 136.43 Boiler ‘pressure? lbs “per sq.) n-gage eee oe 289 294 ‘Turbine chest: pressure——Ib. -per aq. in. gage .; .<. sic eens et ce a, 266 270 superheat at turbine oP. on es ey oe ee ead ae 196 211 Vacuum (referred to 30’’ barometer), inches Hg.........0...c0cccceevccee 28.80 28.58 Pempeérature: ofssea: water OF 02 oe ea a ee 55 74, No, of -circulating (pumps in operation, 370. ic es 2 4 Total DsCocelectnicload kw. se ns cee peo ae 660 885 Fuel oil consumption, Ib. per §.H.P. hr. corrected to 18,5000 B.t.u. pound.... .669 705 ER aR A DY CR aR TTT De RAT Wy RE ROE TED Ns See RO RER UDOT OGRE PCE Got ee shafts, and detecting bearing trouble. For the large amount of auxiliary electric power required by a vessel of such size, there will be four 1800 kilowatts, three-phase, 440-volt, 60- cycle turbo alternators. Two will be located in each engine room and these machines as well as the exciters and motor operated auxiliaries and other circuits, will be controlled from an auxiliary switchboard in each main engine room. In addition there will be two or three 150-kilowatt motor generating sets for obtaining the required voltage for various spe- cial services. In the calculations for fuel oil con- sumption previously given with steam at 400 pounds gage, 700 degrees Fahr. temperature at the superheater steam outlet, the boiler chosen would operate at about 81 per cent effici- ency at sea in ordinary running at full power without air heaters or economizers. With 600 pounds pres- sure and 750 degrees Fahr. tempera- ture, it would seem advisable to in- stall air heaters and some might go so far as to also install economizers. With the design of boiler selected, where there would be a gain in ther- mal efficiency and also in terms of fuel oil per shaft horsepower, there would, however, be increased weight MARINE Review—December, 1931 ledger balance after five or ten years of operation. They have emphasized simplicity, lightness of weight and economical operation with respect to crew and upkeep. The consumption per shaft horsepower on the basis of oil at 18,500 B.t.u. without air heat- ers, is estimated at 0.62 pound per shaft horsepower, both for 145,000 horsepower and also at full power of 180,000 horsepower with 400 pounds at 700 degrees Fahr. at the super- heater steam outlet. The correspond- ing figures with 600 pounds pressure and 750 degrees Fahr. are 0.616. This small gain is mostly due to the increased temperature rather than to the higher pressure. Both figures include all auxiliary consumption, galleys, heating, ventilation and fuel oil heating, refrigeration, makeup feed, etc. which have been carefully estimated and included with that of the main turbine. The calculations are based on boiler efficiencies ob- tained on reliable tests without air heaters or economizers. The use of air heaters, three-stage instead of two-stage feed, heating and motor driven instead of turbine driven, main feed and fuel oil service pumps would further reduce the fuel rate to the following: 0.58 for 400 pounds and 700 degrees temperature 21