Characteristic of marine gearboxes

As we know, an important characteristic of all marine gearboxes is that the gears of both drive trains - ahead and astern - are in mesh all the time, and that selection of ahead, astern and neutral is achieved by using clutches to disconnect whichever drive train is not in use.

There are two main types of clutches: the cone clutch used in the MS2, and the plate clutch used in most of the others.

The plate clutch consists of a stack of flat friction plates. Some of the plates have internal spines which mesh with matching spines on the shaft, so they have to turn with it. Sandwiched between them are similar plates which are free to spin around the input shaft but have external spines that mesh with spines on the inner surface of the clutch casing - connected to the output shaft.