A boat drive has an underwater housing (10) which is arranged outside of a boat hull (7) and can swivel relative to the boat hull (7) about a vertical swivel axis (11). In the housing at least one propeller shaft (13) is mounted and can be driven. A swivel drive mechanism is arranged in the inside space (6) of the boat hull (7) for swiveling the underwater housing (10) in order to control the driving direction of the boat. A zero-position mark (25) is provided on an element of the swivel drive mechanism, which facilitates easy determination of a zero position of the underwater housing (10).