A rotatable propeller drive (1) for a boat, where the propeller drive (1) includes an upper fixing plate (4) adapted for rotationally fixed attachment to the hull bottom (2) of the boat. A lower underwater housing (6) is provided on which at least one propeller (10, 10a, 10b) is mounted, which underwater housing (6) is mounted rotatably in the fixing plate (4) about an essentially vertical axis of rotation (8). An exhaust duct (50) is provided with an exhaust exit (14) located in the underwater housing (6). The exhaust duct (50) has an upper duct section (54) which extends through the fixing plate (4) and has an outlet opening (62) located in proximity to an opposite inlet opening (60) in a lower duct section (56) which extends through the underwater housing (6). One of the outlet opening (62) and inlet opening (60) overlaps the other at least within a limited first rotation angle range for the propeller drive (1). A sliding seal arrangement (58) is adapted for sealing between the upper (54) and lower (56) duct sections, where the sliding seal arrangement (58) includes a sealing element (64) accommodated in a seat (66) around one of the outlet opening (62) and inlet opening (60). The sealing element (64) has a contact surface (68) for sliding contact with an opposite sliding seal surface (70) around the other of the outlet opening (62) and inlet opening (60).