One of several types of transmissions used by the Navy on small craft is the twin-disk. The twin-disk transmission is equipped with a duplex clutch and a reverse and reduction gear unit, all contained in a housing at the afterend of the engine. (See fig. 12-3.) Parts A, B, and C of the clutch assembly are bolted to the flywheel on the crankshaft of the engine and rotate at the same speed as the engine.

Figure 12-3.-Mechanical transmission (twin-disk).

The clutch assembly is contained in the part of the housing nearest the engine. It is a dry-type, twin-disk clutch with two friction disks or clutch plates. Each disk is connected to a separate reduction gear train in the afterpart of the housing. The disk (D) and the gear train for for-ward rotation are connected by a hollow shaft (F). The disk (E) and the gear train for reverse rota-tion are connected by a shaft (G), which runs through the center of shaft (F). Since the gears for forward and reverse rotation of the twin-disk clutch and gear mechanism remain in mesh at all times, there is no shifting of gears. When the mechanism is shifted, only the floating pressure plate, located between the forward and reverse disks, is moved.