A drive unit for boats is described, comprising a transmission with two coaxial bevel gears (6, 7), mounted opposite one another on the same engine shaft (2), which engage a bevel gear (8) fitted to a shaft (3) orthogonal to the preceding shaft (2), and means designed to mesh said engine shaft with one or other of said bevel gears (6, 7), in which said means designed to mesh said bevel gears with said engine shaft are constituted by clutches (11), each housed in a closed seating inside the body of said bevel gears (6, 7).
The engine shaft (2) is mounted on a pair ( or more) of bearings (4) which are mounted on the housing (5) of the device, and said opposite bevel gears (6, 7) are each fitted on one side to a bearing (9) mounted on the housing (5) and on the opposite side to at least one bearing (10), which in turn is mounted on a central support (18) integral with said casing (5), so as to discharge the reaction forces onto the structure of the housing, and not onto the other rotating parts.