Abstract: A robust mechanical actuation design for an autonomous sailing buoy (1) is disclosed based on an internal actuation system. The buoy (1) consists of a simple closed body (3) taking the form of a ship hull to which are attached two fixed appendages (2, 4): one rigid wing (4) to catch the wind, and a keel (2). The design is completely rudderless. Steering is performed using only an internal actuation system. This system includes a moving mass system (5, 6, 7), a processing unit (9), and a navigation unit (8). The navigation unit (8) consists of a GPS, accelerometers and gyroscopes, and a wind direction and velocity sensor. The processing unit (9), using information given by the navigation unit (8), automatically controls the moving mass (6) to hold the buoy (1) on a desired course.