The fluid clutch (coupling) is used in some Navy ships. A hydraulic coupling eliminates the need for a mechanical connection between the

Figure 12-9.-Schematic diagram of reverse gear lubrication system.

engine and the reduction gears. Power is transmitted through hydraulic couplings very efficiently (97 percent) without the transmission of torsional vibrations or load shocks from the engine to the reduction gear. The power loss from the small amount of slippage is transformed into heat, which is absorbed by the oil in the system. Some slippage is necessary for operation of the hydraulic coupling, since torque transmission depends on relative motion between the two rotors.