Abstract: A propelling device for a propeller-driven boat comprising a longitudinally extending tunnel disposed at the aft portion of the boat housing a propeller for rotation at a level above the keel of the boat. A pair of deflector fins are pivotally carried for rotation about parallel vertical axes located on opposite sides of the longitudinal axis of the tunnel at a position rearwardly of the propeller. A curved deflector plate is pivotably supported for movement about a horizontal axis rearwardly of the fins for movement between a raised inoperative position and a lowered operative position.