Abstract: The invention is a manoeuvring device for boats, comprised of a pair of pivotal tube plates (17, 18) mounted outside a propeller 14 and, under normal operation, forming a tube (19) around the propeller. These plates can be swung to one side relative to a medial position to enable sideways steering of the vessel, and be brought together astern of the propeller to form a blade when reversing. The tube plates (17, 18) extend down beneath the propeller (beside 19B). A tube wing (20), extending in a longitudinal direction, is mounted immediately beneath the propeller (14) and is arched upwards towards the propeller wings. Under normal operation, a tube that is sickle-shaped in cross section is delimited between the tube wing and the lower portion of the tube plates. The pivot axis of the tube plates (17, 18) is preferably located close to the propeller wing plane.