A marine propulsion unit including a rotary casing rotatable about a central axis A, and blades extending axially from the rotary casing for rotation with the rotary casing about the central axis A, wherein each blade is mounted for pivotal movement about blade axes B. A blade shaft portion of each blade is at least partly surrounded by a blade housing and by a blade portion of each blade is outside the blade housing, wherein the blade housing is releasable attached to the rotary casing, and each blade being supported in the blade housing by means of bearings for the pivotal movement.