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er amount is used, but the efficiency is more nearly maintained than in a marine turbine where variation of power is only obtained by varying the speed. There are, therefore, two means by which the full efficiency of the turbine may be obtained: (1) running the turbine at the highest practicable rey- olutions, trusting to some transmis- sion system will revolve the propeller at the speed of its maximum eficiency; (2) varying the power de- livered by the turbine without varying the revolutions very much. It is evi- dent that the suggestion of mechani- cal gearing already made could not easily fulfill both conditions. The ob- which vious method to adopt to secure these means is that of electric transmis- sion by dynamo and motor, the dy- namo running at high revolutions and practically constant speed whatever electric power is given off by it, while: the motor is running at varying speed according to the electric power put into the propeller. The question then arises what kind of efficiency such a combination will have, as there are transmission losses, and unless these are less than the gain in pro- peller and turbine efficiency, there will be no net gain. If we assume that 'the propeller can be run at a speed which has been found to be efficient in the reciprocating engines, we may compare the efficiency with that of propellers. used in similar vessels hav- ing turbines directly connected. The cross-channel steamers Antrim and Londonderry, the Cunard steamers Caronia and Carmania, and the cruis- ers Topaze and Amethyst are cases in point, having respectively in each class reciprocating and turbine en- gines. The best figures available give in these classes respectively, relative differences in efficiency of 10 per cent, 7 per cent and 6 per cent. The losses in transmission may be put at not more than 10 per cent, so that there appears to be a prima facie case for further investigation. Some of the cases taken for vessels with. reciprocating engines, to some extent, suffer for the same réason that the turbine does, namely, that in order to economize weight of éngines, rev- olutions are made higher than they Would - be for best efficiency of pro- Deller, Electricians will at once point out that in a motor on a propeller running at varying powers and speeds, the change of speed in the motor is usu- ly associated with 'the - absorption of ower in the speed changing devices, 'THE Marine Review or there will be other: equally dis- advantageous features' in the motor. Mr. Mavor, of Glasgow, who has given considerable attention to this subject, claims to have: surmounted this diffi- culty by (1) adopting the multiphase alternating current~ system "in the dy- namo and motor; (2) by the inven- tion of a ditecentint motor consisting of two motors mounted co- axially. One running outside the other. Mr. Mavor says:--"Motors are con- nected in- such Mmannet that. - the speed variation may be effected as follows: "For slow speed, by running the regulating motor in the reverse di- rection to the direct connected motor. "Ror intermediate speed, by run- hing the -- direct connected motor alone, the regulating motor being stopped. "For full speed, by running the reg- ulating motor in the same direction as the direct connected motor. "This arrangement requires no spur wheels or friction gearing. Each motor is controlled by a simple re- versing switch, without any other mechanism, and there are no power wasting devices. : "The advantages of the oe of this system are well illustrated in the case of a ship of 17,000 horsepower on three propellers at 21 knots maxi- mum speed. At full speed the 17,000 -H. P. is provided by one turbo-gener- ator of 10,000 H. P., which directly drives the. direct connected motors, and by-a generator of 7,000 H. P.,, which drives the regulating motors, whole plant being run at full speed and full power. When 18 knots, the 7,000 H. P turbo-gener- ator is stopped, and the coal consump- tion per horsepower is the same at 18 knots: as at full speed. When the speed is further reduced the 10,000 H. P. may be stopped and ae smaller unit again applied. "It will thus be seen that in addi- tion to the economy attainable at full speed, there is a very great im- "provement in economy at all lower speeds, owing to the possibility of choosing a Suitable size of power unit for each speed.. This advantage also appears in cases where the pow- er required to drive the ship, at any given speed, is varied by the condi- tion of weather or load; in short, the electric arrangements provide a means of approximating at all working speeds of the ship to the economy at- 'on the trial trip at full tainable Tt. 35; of course, obvious that speed. fore, 'the. speed is dropped from 21 knots to limit US at very low speeds of the ship the economy cannot come within. this region, but on the electric arrange- ments it is very much better than that attainable by the ordinary means." These powers, will, therefore, all be developed at much higher efficien- cies than in the present marine tur- bine as connected directly to the pro- peller. For powers between any of these named, variations in the speed of the dynamos are necessary, but they are not great enough to seri- ously alter the efficiencies. Electric transmission may, therefore, be con- sidered as one of the propelling pow- ers of the future. Whether the: sys- tem of motors proposed by Mr. Ma- vor fulfills all the conditions necessary for adoption time will show, but it certainly is well worth considering by anyone contemplating new ships. It has the merit of being equally pow- erful ahead and astern, and avoids the -- difficulty of reversing which turbine driven vessels have sometimes been supposed to possess. It has the furth- er merit that no individual feature of it is new or experimental. Large propellers are not new, motors are not new, and turbines of constant speed are in common use. There ap- pears' to be no possibility of failure in it on account of the elements of the combination. The Mavor system of electric trans- mission, as described, is for steam driven turbines, and does not, there- deal with the boiler, except in so far as the gain in efficiency may reduce the amount of boiler neces- sary to be carried. It may, however, be applied to other systems of power where electric transmission is of ad- vantage, i. e, where the electric generator has a_ high _ efficiency ot. weight, «. power'. or cost. at revolutions too high or too low to suit the most efficient screw by direct connection. For instance, a series of internal combustion engines of high speed and small power may be used to create current which could be poured into motors driving pro- peller shafts at efficient revolutions. Such a combination would dispense. with boilers and coal in bunkers, whose place would be taken by petrol or petroleum in tanks, or perhaps by producers using less coal. There is no doubt of the superiority in fuel efficiency of the internal combustion engine, but in considering weight. ef- ficiency it has to be borne in mind that this can only be secured in the andiva is imposed by the engne by high revolutions, . to. these-.