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48 in such manner that the speed varia- ition may be effected as follows: For slow speed, by running the reg- ulating motor in the reverse direc- Stator THE Marine. REVIEW speed, is varied by the, condition of weather or-load;din:short, the electric arrangements provide a means of ap- proximating at all working speeds of ee ee SSS SE FIG, 3--ELEVATION AND SECTION, tion to the direct connected motor. For intermediate speed, by running 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 mo- tor is controlled by a simple reversing switch without any other mechanism, and there are no power-wasting de- vices. ay The advantages of the adoption of this system are well illustrated in the case of a ship of 17,000 horsepower on three propellers at 21 knots max- imum speed. At full speedthe 17,000 horsepower is provided by one tur- bo generator of 10,000 horsepower which directly drives the direct con- nected motors, and by a generator of 7,000 horsepower which drives the regulating motors, the whole plant being run at full speed and full pow- er. When the speed is dropped from 21 knots to 18 knots, the 7,000 horse- power turbo generator is stopped, and the coal consumption per horse- power is the same at 18 knots as at full speed. When the speed is further reduced the 10,000 horsepower may be stopped and the 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 improve- ment in economy at all lower speeds, owing to the possibility of choosing a suitable size of power unit for each speed. This advantage also ap- pears in cases where the power re- quired to drive the ship, at any given the ship to the economy attainable on the :trial, trip' at full speed) - It-is'of course, obvious' that at very low speeds of the ship the economy can- not come within this region, but on the electric arrangements it. is very much better than attainable by the ordinary means. The model has been made. with ball bearings, but it is not proposed to use these in the actual machine which will be arranged as shown in Fig. 4. The rotor circuit -and the induced circuit on the spinner are permanently closed, being of what. is -engine room arrangement of a cargo vessel - cordance fitted with reciprocating en- gines. of about 1,200 horsepower, and supplied with steam from two _ boil- ers. This ship is constructed under the patents of Henry Burrell, who has been good enough to supply the au- thor with the drawings. The existing plant is shown in shade. The equiva- lent electric plant is shown in outline. The space occupied and weight are about the same in each case. This paper is an incomplete treat- ment of the subject, but it may serve to elicit a discussion interesting to members of the institution and others. The author acknowledges gratefully his indebtedness to Thomas Bell, who specially directed his attention to this subject, to Prof. Biles; who has for many months lent his knowledge and experience in preliminary discusssions, and who it may be hoped will con- tribute to the public discussion, also to Mr. Luke, Mr. Cleghorn and to. Dr- Caird, all of whom have taken a lively interest in these investigations and proposals. APPENDIX. NOTE ON SCREW PROPELLERS. The propeller is one of the many things on. which Professor Macquorne Rankine turned the searchlight of his genius, and the writer was, early in his investigations, referred to an interesting paper by W. McEntreé on "The Limit of Propeller Efficiency,"* where he showed that a curve of "ideal efficiency,' drawn in ac- with Rankine's suggestions, could be compared with the results of ELECTRIC GENERATOR fae gtec omens al Nee ee es MN FIG. 4--LONGITUDINAL SECTION, known as the "squirrel cage" type, the simplest of all forms of winding. Figs. 4 and 5 show the longitudinal and cross sections respectively of the Taylor's experiments, which are well | known to naval architects. *Trans. American' Institution of Naval Archi- tects, 1906.