A robot (2) and method for underwater monitoring and maintenance of a ship's hull (1) when the ship is underway, are described. The robot (2) comprises a main body (5), a connector (21) for connecting the robot (2) to a cable (3) for towing the robot (2), a resting base (13) adopted to rest against the ship's hull (1), one or more hydrofoil(s) (6, 7) arranged perpendicular to the length axis of the main body (5), and a rudder (8) arranged at the front part of the main body (5), the main body (5) being a straight and elongated body having a length to width ratio of 5 or more, where the length of the hydrofoil(s) (6, 7) as seen perpendicular to the main body (5), is/are longer than the width of the main body (5), and where the connector (21) for the cable (3) is arranged at one end of a hydrofoil (6), or at an arm extending parallel with the one or more hydrofoil(s).