140 ELECTRIC PROPULSION OF SHIPS. 



form of rings in the magnetic circuit, two of which are driving and two of which are driven. 

 The flywheel proper accommodates an exciting coil (shown in Fig. 2) producing the mag- 

 netic flux. At all fractional speeds, or while this clutch is slipping, large currents are gen- 

 erated in the driven elements by magneto induction, which are now acting as short-circuited 

 secondaries, producing heavy drag torques under perfect control by varying the amount of 

 coil excitation. This is. plainly seen by the height of the curve at the right in Fig. 4, Plate 

 27. However, when the speed comes up in the vicinity of synchronism, shown at the extreme 

 left in Fig. 4, locking occurs and the parts assume the relative position shown to the right in 

 Fig. 3, where enormous pull-out torques are present, as indicated by the height of the curve 

 at the extreme left, as stated. 



In Fig. 5 the casing containing the low-speed gears is an entity by itself, especially with 

 respect to any extreme alignment requirements with the engine. The air gaps in the flywheels 

 allow of considerable leeway, both endwise and laterally. The pinions are mounted on hol- 

 low quills, and complete flexibility is assured by the steel plate coupling located at the after 

 end of each pinion. No amount of "weaving" of the foundations forming a part of the ship's 

 structure, in changing the alignment, will disturb the perfectly smooth running of these low- 

 speed gears. 



With this clutch and the engine combination shown in Fig. 5, several very important 

 advantages are secured : 



1. We have available on a single propeller all the advantages and flexibility of a multi- 

 ple engine equipment, where one engine may be shut down and completely disconnected for 

 inspection, valve grinding, etc., and yet the ship is going forward at three-quarters its nor- 

 mal speed. 



2. We have the complete flexibility of the electric drive without the expense, weight and 

 space of the electric generators and motors, as stated, and the cumbersome electric control 

 equipment for handling the heavy currents in maneuvering, and the double losses of genera- 

 tors and motors which are of substantial amoimt and a constant drag on plant and fuel 

 economy. 



3. The simplest form of gear drive may be employed because the magnetic clutch allows 

 the pinion to be a complete "floater." The pinion may thus accommodate itself to any want 

 of precision and all sorts of idiosyncrasies of the main gear and teeth without shock. Any 

 irregularities existing in either main gear or pinions thus have to deal only with the small 

 masses of the pinion itself and its stub shaft, being completely isolated from the large mass 

 moments of the engine. 



4. The torque, being under complete control, can be lowered so as to safeguard the 

 equipment against overloading, especially when sailing in obstructed harbors, near derelicts, 

 and where floating obstacles are likely to be encountered by the propeller blades, thus provid- 

 ing an important emergency disconnecting gear breaking away from the large revolving en- 

 gine masses and allowing the propeller to "stop in its tracks" through the self-interruptibility 

 of the magnetic clutch when reduced to fractional underload condition. In this way many 

 disasters to the propelling machinery and interruptions to the service may be avoided. 



5. Most revolving machinery is subject to periods, sometimes running into severe "criti- 

 cal." These criticals always develop from the torque irregularities in the revolving masses 

 within the engine pitted against outside mass moments aft. This can occur only when these 

 are solidly coupled with each other, but if instead they are isolated, as by the air gap of the 

 magnetic clutch, these troublesome criticals with their excessive stresses are completely sup- 

 pressed and can never develop. 



