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September, 1913 inherently unfit, without saying that in certain classes of vessels where the conditions are special there may not be a perfectly legitimate field for the type criticized--viz., the direct-drive, slow-speed, two-cycle open marine en- gine. Such scope is most assuredly not found in the full-bodied cargo boat, still less in the Canadian canal vessel, under the peculiar conditions and limitations above described. It is unthinkable that, with its present form of hull, which cannot be varied, and the still more definitely fixed type of propeller, the present triple-expansion engine can be displaced by any direct- connected Diesel engine. Eighty rev- olutions per minute, which is common with the steam engine, is almost hope- less for the Diesel, and however suc- cessfully the reversing gear may op- erate in the latter engine, it is little likely to be improved by hundreds of rapidly alternating go-ahead and go- astern motions required in negotiating such a series of locks as in the Wel- land canal. Introduction of Electricity Broadly speaking, the introduction of electricity in this connection puts the Diesel engine back into work for which it is eminently suited, under conditions which give it every chance to maintain efficiency and reliability. - It is as far as possible removed from the uncertain action of the propeller, and the uneven loading and vibration incidental to a direct propeller drive. In Canadian canal work the power required for propulsion varies between very wide limits. In the canals them- selves, four miles being the limiting speed, 150 i. h. p. or less is sufficient, though full speed must be always available for emergency, especially in backing. In the open lake in fair weather 500 i. h. p. is sufficient to maintain fair speed, while 750 i. h. p. is necessary in contending with the St. Lawrence currents. In some de- signs the writers, therefore, proposed three Diesel generating units of 250 i. h. p., each of which can be switched on to the propelling motor as re- quired. Such an arrangement is shown mr igs, 13° 12° and "io.2 Un. the Tynemount, which is now building, to demonstrate the Diesel-electric ar- rangment of propelling machinery, a two-unit subdivision is arranged for, each unit furnishing 300 b. h. p. Figs. 14 to 18 show approximately the gen- eral layout of the installation and attention is directed in this illustra- tion, and also in Figs. 11 to 13, to the ease with which the generating units can be located in any desired position, in a separate engine room remote from the propeller motor, or on an THE MARINE REVIEW upper flat, or as may be considered convenient. The electric system adopted is that identified with the name of the second writer, involving the use of alternating current. Investigation and actual tests have amply shown the suitability of this system for marine propulsion. This system has for its special object the simplification of the electric equip- ment. Many applications of electric power have been made to marine pro- pulsion, but hitherto, with the excep- tion of the Electric Arc, propelled on this system and built in 1911, contin- uous currents only have been used, the reason being that regulation of speed and control is easier for con- tinuous current under ordinary condi- tions than for alternating current. The disadvantages attached to the use of alternating current in respect of reg- ulation are associated with the greater number of conductors and particularly with the property of alternating cur- rent motors, that the speed of the motor bears a fixed ratio to the speed of the generator, and that any de- parture from this speed is associated normally with loss of efficiency and with more or less complicated devices for changing the frequency of the cur- rent alternations. In the system under notice these difficulties are overcome by the use of more than one frequency applied to each individual motor. The currents of different frequency are carried in independent, mutually non-inductive circuits, the magnetic systems being entirely independent, but operating up- on a common rotor, so that their mechanical effects can be superposed and the power transmitted in the sep- arate circuits combined to produce the required mechanical effect. The re- quired currents may be obtained from one or more generators. The Tynemount In the vessel now under descrip- tion (the Tynemount) the equipment consists of two three-phase genera- tors driven by Diesel engines running at 400 revolutions per minute. _ The electrical output from each set is 235 kilovolt-amperes at 500 volts al- ternating. The generators have 6 and 8 poles respectively, giving fre- quencies of 20 and 26.6 per second. The exciting current is obtained from direct-connected continuous-current machines on the same shafts as the alternators. The normal exciting cur- rent is 30 amperes at 100 volts. A single three-phase motor is coupled 'direct to the propeller-shaft, which is of the ordinary type with marine thrust-block. The motor develops 500 shaft horsepower. The rotor or mov- oF ing part is of the simple squirrel- cage type, without any electrical or mechanical connection other than its rigid attachment to the propeller- shaft. The stationary part of the motor has two separate non-inductive windings for 30 and 40 poles respect- ively. When each of these two wind- ings is connected to the appropriate . generator, the speed due to each is 78 revolutions per minute. By chang- ing the connection on both windings, the direction of rotation is reversed, and by connecting the 40-pole wind- ing of the motor to the 6-pole gene- rator, the speed in either direction drops to 58 revolutions per minute, or about three-quarters of the full revolutions. If full speed be not re- quired, one generator may be stopped and the other left running at full revolutions under governor control and at full economy, because the power required to drive the ship at three-quarters speed is about half of that required to drive it at full speed. If either of the generators be left attached to its own winding and the other generator shut down, the ship is propelled by either engine at a little over half-speed, the speed of the ship falling with the speed of ro- tation of the engine, until an auto- matic adjustment of power and speed is reached at about half-speed. Control Gear Apparatus The control-gear consists of an ap- paratus for changing the connections of the generator and motor windings respectively. There are five positions on the switch, corresponding to the ordinary positions on the engine- room telegraph. They are "Full Speed Ahead", "Half Speed Ahead", "Stop", "Half Speed. Astern", and. "Full Speed Astern"'. Each position of the controller is definitely fixed by means of cams and rollers, so that stopping at intermediate positions is prevented. The controlling gear provides for the interruption of the excitation of the generators while the switch is being moved from one step to another, the exciting switch and the main switch being interlocked so that the switch- ing-over operation is accomplished while the electric circuits are "dead", thus avoiding injurious sparking. Should it be found convenient, a very simple arrangement could be made whereby the control could be operated from the bridge of the vessel, and the engineer's attention confined to the keeping of his engines lubricated 'and supplied with fuel to run at con- stant speed. It will be seen that this method of control entirely dispenses -with the stopping and starting of the Diesel engines for manoeuvring, an