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October, 1910 TAE Marine Review 407 ELECTRO-MAGNETIC TRANSMISSION FOR MARINE PROPULSION' 7T IS now generally admitted that the combination of a reciprocating engine with an exhaust steam turbine pro- vides the most sat- isfactory solution of of marine propulsion, problem whenever a high efficiency is of para- the mount importance. However, when he comes to put this principle into prac- tice, the marine engineer is soon con- fronted with a number of difficulties which, while not actually insuperable, are only got over at the cost of both the efficiency and simplicity of the ar- rangement. The use of two propellers driven by the reciprocating engine and by the turbine respectively need hardly be taken into consideration on ac- count of the great difference between the speed and brake horsepower of both machines. Under these condi- tiotis, the only solution lies in an ar- Tangement whereby the power of the turbine is transmitted, at a suitably reduced speed, to the main, or recip- rocating engine shaft, -so as to as- sist the Jatter in the propulsion of the ship. A mechanical »speed-reduc- tion gear suggests itself as the sim- Plest realization of this arrangement. eae : é Read at the Naval and Enginering Exhi- bition, Olympia, on Saturday, Sept. 17. By Jures Lecocue. However, it must be remembered that, under certain conditions of the sea, the reciprocating engine of a boat shows a marked tendency to race; a tendency which is by no means equally shared by the turbine. Difficulties of the Problem. If, therefore, the connection be- tween both machines is effected by means of the usual system of gear- ing, the teeth of the latter will in all probability be stripped off, as soon as, from some reason or other, the resistance on the main shaft is ap- preciably reduced. If to this we add 300-H. PB Macneric Gear, SPEED 3000/75. the noise, vibrations, wear and tear and the comparatively low efficiency of mechanical gearing for such high ratio as 3,000/75 R. P. M., it will be reasonably admitted that no mechan- ical gear can, afford a satisfactory so- lution of the problem before us. Oth- er. means' for transmitting power and simultaneously reducing theé"' speed are the hydraulic and electrical trans- missions, both of which have been tried in connection with marine pro- pulsion. The former alternative, as conceived at present, can' hardly be expected to meet the requirements of the marine. engineer on account 01 its comparatively low efficiency, ex- cessive wear, weight and cost. The second alternative, namely, the elec- trical transmission, appears very at- tractive from the point of view of flexibility and ease of control. How- ever important these factors undoubt- edly are, other conditions must be complied with before an_ electric transmission. can be conveniently adopted for the purpose in question. The first of these conditions is a high efficiency. In speaking of this system as a "transmission," one is apt to forget that the actual trans- mission is only part of the process, the latter being essentially a "trans- formation" of mechanical power into electrical energy, and again of elec- trical energy into mechanical power. Taking into consideration the indiv- idual efficiency of each single element (generator and motor) of this trans- mission, it will be found that the combined efficiency cannot be very high, especially when the motor is designed to run at such low speed as 75 R. P. M. Other. serious draw- backs of this system are the weight and cost of the slow-running electric motor and also the necessity of re- sorting to high tension voltage, the presence of which is more or less un-: welcome aboard ships. Application of Magnetic Gear. The gear" application of the "magnetic to marine exhaust-steam tur- bines was suggested on account of its high efficiency, noiselessness, positive drive, cheapness of upkeep (there be- ing no wear and no need for lubri- cation, except in the bearings) and, last but not least, on account of this valuable peculiarity that, as soon as the reciprocating engine begins to race, the transmission comes -auto- matically out of gear, thus effectively protecting the machinery against in- jury. Compared with both dynamo and motor, the magnetic gear has the advantage that it requires only a nominal amount of electrical energy. In fact, the latter is only an, acces- sory, and the current being of. com- paratively low voltage can usually be supplied. by. the existing lighting. sets. Although, the simplicity of construc- tion and action of the magnetic gear is almost suggested by the name it- self, I think a brief description of the machine may be found of inter- est. ft The illustration shows a magnetic PE EN ME ie. Ys SIS LE OED