Cylinder-driven marine propulsion system

A marine propulsion system includes a hull-contained, open-ended duct extending from bow to stern along the bottom of a vessel, the top of the duct being disposed above the water line and all duct walls extending parallel to the axis of motion of the vessel. Buoyancy chambers extend along the top and sides of the duct from a location aft of the duct inlet to the stern and converge at their forward end to define a venturi throat. A reaction device, located aft of the duct inlet and forward of the venturi throat, imparts rearward flow velocity to water in the duct. In one embodiment the reaction device is a partially-submerged horizontally-extending cylinder oriented perpendicular to flow through the duct. The cylinder, when rotated, increases water flow velocity in the duct and additionally pumps the water toward the throat in which the water experiences further flow velocity increase. In a second embodiment the reaction device is an air nozzle which issues high velocity air into the duct in a rearward direction at a slight angle toward the water surface from a location above the surface.