NOVELTY - A vessel includes a hull, a propeller for vessel propulsion, and at least one rotatable cylinder (6) assuming an operational state vertically mounted on the vessel. The cylinder has a rigid outer surface, a motor drive (8) for rotating the cylinder around the longitudinal axis, and a displacement member (7) for displacing the cylinder to an inoperational position. The motor drive is situated at a constant vertical position inside the cylinder, particularly its lowermost segment (9).    USE - Vessel for sailing operations.    ADVANTAGE - The motor drive is situated inside the cylinder, reducing use of deck space and shielding the motor from environmental conditions. The cylinder can be reduced in size conveniently, such as when sailing against the wind or during severe weather conditions, since the cylinder comprises tubular segments telescopically connected together. The outer surfaces of the segments overlap when the cylinder is in inoperational state, protecting the cylinder from environmental conditions. Due to its reduced size in inoperational state, the cylinder can be easily exchanged in case of defect, or can be easily accessed for repairs. The motor drive can be put at a more beneficial height within the cylinder to reduce vibrations. The cylinder is connected to the vessel about a horizontal hinge line, allowing for deck space savings and easier access to rotor parts. Having the drive member on deck allows for relatively easy access to the motor for maintenance and inspection. Having a transmission device attached to a vertical segment allows for good flexibility for detaching the transmission device and the drive member. The cylinder is placed with its longitudinal axis into the horizontal position, consuming even less deck space and minimizing unwanted rotor drag. Retracting the cylinder below the deck ensures optimal use of the area in the hull. Storing the cylinder in the cargo space locates the cylinder out of the way of deck operations, and shields the cylinder from environmental conditions.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic cross-sectional side view of the cylinder.    Cylinder (6)    Displacement member (7)    Motor drive (8)    Lowermost segment (9)    Extension member (10)