Friction clutches are most commonly used with smaller high-speed engines. PNEUMATIC clutches, with cylindrical friction surfaces, are used with engines up to 2,000 hp.

There are two general types of friction clutches: DISK and BAND. Disk-type clutches are classified as either MECHANICAL or HYDRAULIC. Because of the wide use of the disk-type clutch on small craft, our discussion in the sections that follow will include both the mechanical and the hydraulic types.

Friction clutches are engaged when two friction surfaces are mechanically forced into contact with each other by toggle-action linkage through stiff springs or through the use of hydraulic or pneumatic pressure.