Torsional Vibration in Marine Propulsion

2.4.1 Couplings.
Elastic or flexible couplings allow slight misalignment and damp out or remove torque variations from the engine. The coupling may in addition function as a clutch or disconnecting device. Couplings may be mechanical, electrical, hydraulic or pneumatic in operation. It usual to combine the function of clutch with a coupling and this is not readily possible with the mechanical coupling.4
Claw type flexible couplings suffer from unpredictable friction forces between the teeth. Not this only accelerates the wear and necessitate adequate but it can cause undesirable bending effects on the pinion shaft, and thus interfere with the tooth action. Membrane type flexible couplings do not suffer from such friction forces, nor do they require any lubrication. Any relative axial movement between the shafts or any transverse misalignment is accommodated by flexing of the membranes.6
2.4.2 Clutches.
A clutch is a device to connect or separate a driving unit from the unit it drives. With two engines connected to a gearbox a clutch enables one or both engines to be run and facilitates reversing of the engine.
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