Abstract: Marine propulsion apparatus comprising an engine mounted within a buoyant enclosure, which is adapted to be connected to a marine vessel, which requires propulsion. The engine drives a propeller through a simple drive system. The apparatus is adapted to be fitted into position on pivotal mountings for steering purposes, and may itself be fitted with steering apparatus such that it may be maneuvered independently of the marine vessel for positioning relative to it. The enclosure is sized to permit access around the engine for in-situ maintenance and repair.