A radial vane fluid motor or pump has an open ended tubular rotor having a cylindrical outer surface rotatably mounted in a tubular stator having its inner surface contoured to provide successive portions of increased and decreased spacing relative to the rotor body. A plurality of elongated movable vane assemblies are mounted on and project outwardly from the rotor surface to continuously contact the stator surface. Bearings support the rotor within the stator, and seals are provided for sealing the space between the rotor and stator. Pressure inlets and exhaust ports are provided in the stator to permit the flow of pressure fluid into or out of the device. Mounting the vanes on the cylindrical rotor surface enables production cost reduction and simplifies maintenance. A conventional propeller mounted in the cylindrical rotor provides an improved shrouded propellor propulsion system for marine vessels. Mounting the system on a vessel for rotation about an axis perpendicular to the axis of the rotor enables steering of the vessel without use of a rudder.