Design of a free-rotating wing sail for an autonomous sailboat

Sammanfattning: There is an accelerating need for ocean sensing where autonomous vehicles can play a key role in assisting engineers, researcher and scientists with environmental monitoring and colleting oceanographic data. This thesis is performed in collaboration with a research group at The Royal Institute of Technology that currently develops an autonomous sailboat to be used as a sensor carrying platform for autonomous data acquisition in the Baltic Sea. This type of vehicle has potentials to be a helpful and cheaper alternative to a commercial research vessel. The thesis presents the design, construction and experimental testing of a rigid free-rotating wing sail for this autonomous sailboat. The goal is to design a rig that can sustain under all occurring weather conditions in the Baltic sea while ensuring sailing performance, robustness, reliability and low power consumption, which are key aspects driving the design. The rig is designed through the utilization of analysis and design methods involving a Vortex Lattice Method combined with a Velocity Prediction Program in order to achieve best possible aerodynamic performance with respect to the application requirements. The rig is manufactured as a sandwich structure with a light core material, reinforced with fiberglass and laminated using advanced resin technology. The main challenges in the development process are structural arrangement, rigidity and weight as well as integration of subsystems and achieving overall robustness. Initial experimental testing, sailing under radio control, has been performed showing promising results. The vehicle was operated under moderate weather conditions, 8 – 10 m/s NE winds, at Baggensfjärden, Sweden, where expected behaviour, wing structure rigidity, boat speed and manoeuvrability was successfully demonstrated. Future challenges are now to further develop navigational control and guidance strategy, pushing the technology front forward in autonomous sailing.