P. & O. STRAT

Hokitika Guardian, 30 June 1931, Page 5

P. & O. STRAT

— — POWER STATION AFLOJ^^| electric it:opulsion. Shrink the power station of a big city, to a size which will fit a 22,000-tou ocean steamer; transmit the huge output- resulting into motors so great that a man is tiny by contrast ; couple the driving force of these motors to soii.t steel shafts connected with immense propellers—and one will have a crude illustration of the electric propulsion of the new <P. and 0. steamer Strathnaver. The engineer on the control platform of the Strathnaver has the same command of his vessel that. the driver in the cab of an electric locomotive has of his train. He can pull up'.quickly from full speed ahead, choose his speed, reverse, vary one propeller independent of the other, etc. In a smooth sea he can cut down his power, emergency calls, lie can utilise the full energy which will force the Strathnaver ahead at 22 and more knots to the hour. In essence the Strathnaver is controlled as simply as the electric light in the home—or the electric iron or electric torch, ,\ncl it has the advantage of being fool proof. It, is no more possible to make a mistake through negligence than it js possible for the automatic apparatus -in a railway signal box to open one set of lines before the other is clear.

One striking sequel to electric propulsion is the absence of vibration in public rooms and cabins, The man on the bridge has a highly flexible command, which can turn sharply, stop, manoeuvre, and be immediately responsible to every need.

The Strathnaver and Strathaird have followed the triumph achieved by the new Viceroy of India, the P. and O. steamer which was the first electricallypropelled passenger vessel built in 'England.

THE TURB 0-GENERATORS. The four mammoth oil-fired boilers work at a pressure of 400 lb -to .the square inch—it seems . only yesterday that the maximum of pressure was considered 2151 b to the square inch; y - Another forward. - step is the superheating of the steam to 725 degrees Fahrenheit. This super-heating takes place after the steam leaves the boilers,' and is secured by its passage through tubes surrounded Oy intensely, hot, gas-.s which would ordinarily- escape by the funnels. Thus treated, it- becomes so dry that it is really an invisible gas. The drier and more gaseous the the mows it conforms to the laws governing gases, hence -the more effective it becomes for propulsion. The steam passes through and drives a turbine which works an electric generator.—the two are combined in one unit as a turbo-generator. The very high voltage of 300 U odd is transferred as alternating current to the. motors: The fact that within recent times the limit of voltage allowed in a steamer by the o)djl> ilos* and that the power-house current which lights a home is only about 250 volts, gives a truer conception of the enormous possibilities behind a driving force of 3000 volt ST- And that is only the energy supplied by one or the turbo-generator a of the Strathnaver, In addition, thertare auxiliary turbo-generators which supply' 240 volts for lighting, power, ventilation, and cooking. ELFOIIfMO PROPELLING MOTORS. The driving motor is at one end of the propeller shaft and the propeller at the other. In miniature the • operatic: resembles that which , drives an electric fan in an office,

To .the average man the fact that there is a driving force of 28,000 horsepower applied to the propeller shaft,; means little. The transmission of th driving force to the propellers seems on the face of it the simplest part of th ■ problem. 'But as a matter of fact th. propeller is a slow-moving thing amhigh revolutions would be fatal to speed. Although the Strathnaver's propelle. turn at 125 revolutions a minute, which is probably faster than anything abov the destroyer class, it is a. snail par. compared with' the 3000 revolutions o; the turbine in the turbo-gmierator. The whole objective, therefore,electr _ propulsion is to transmit— iwitjkout los; of power—the energy of a . very fastrunning turbine to the slow-funning propeller. ,

Until the advent’ of the Viceroy India, this was accomplishecUby means of mechanical reduction gear, that; is bv a set of helical gear wheels interposed bv tween the turbine shaft afl'fiuthe pro peller shaft. These wheels .■wore heavy and cumbersome, and had other, some t : mes costlyy- disadvantages, . In th< Viceroy of India and the ; Strathnav the electrical transmission couples i-h turbine directly to an alternating cu: rent generator ana transmits the curre'.n therefrom through electric wires {cor. due-tors) to a slow-running motor direct lv coupled to the propeller shaft. The former difficulty of reversing tur bine machinery, when using electr:* transmission, is also overcome. All the; is now necessary in reversing is to man* pulate the electric current to the pro pulsion motor—'the turbo-alternator rur n ! ng all the time in one direction. I • the case of the old mechanical reduction gearing it was necessary to have separat ‘•astern” turbines incorporated in th* ‘‘ahead” turbine casing.

Here are the interesting reactions: tlr size and shape of ship and the speed r qnired dictate, the size of the propeller? the size of the propellers regulates thSize of the propulsion motors attache' to the propeller shaft; the size and pow er of these motors in turn fix the si; and output of the tur,bo-alternators. Tht Mrathnaver will leave England ohm- maiden voyage to Australia on Oeto ber 2.