Towards Heading Control of an Autonomous Sailing Platform through Weight Balancing

Autonomous sailing platforms or sailing robots are a class of autonomous surface vehicles using only the wind as their means of propulsion. In order to adapt to harsh conditions at sea, a robust design of an autonomous sailing platform is presented in this paper. The proposed sailing robot consists of a hull to which are attached a fixed and rigid sail, and an internal moving weight system used for steering. The control objective is to maintain a desired heading angle for the platform by automatically controlling the movable mass. Two different weight balancing mechanisms, i.e. a so-called linear weight mechanism and a pendulum mechanism, are introduced together with the mathematical model of the vehicle, exposed to ocean currents and wind variations. Furthermore, to allow maneuverability, dimensioning of the mass weight and the vehicle beam (or the pendulum length) are considered through simple nonlinear controllability properties using flatness theory. Finally, we present an exponentially stable heading controller based on backstepping and contraction theory, and which explicitly takes into account the presence of currents.