Abstract: A thrust propulsion mechanism (10) for a boat (12) includes an outlet conduit (22) extending athwartships from a first outlet port (16) to a second outlet port (16') in the hull (18). A paddle-wheel impeller (24) is mounted within the hull for rotation about an axis of rotation (34) by a reversible motor (30). A circumferential paddle (58) portion of the paddle-wheel impeller extends into an aperture (26) defined centrally in the top wall of the outlet conduit. An inlet conduit (20) extends athwartships from a first inlet port (14) to a second inlet port (14'), and intermediate thereof supplies water to the center of the paddle-wheel impeller. Water is discharged from the paddle-wheel impeller through one of the outlet ports, dependent on the direction of rotation of the paddle-wheel impeller, to create thrust by a combined paddle-wheel and centrifugal pump action.