Preliminary Design of a Dual Propulsive/Regenerative Device for Sail Ships: SAIL-POD by Velettrica

Nowadays, the necessity to reduce the environmental pollution and to prevent the ecosystems damages by human-induced activities can be undertaken by adopting solutions that increase the overall sustainability. Specifically, in the frame of marine transportation, the reduction of the dependency from the fossil fuels is approached with the development of existing systems as well as the discovery of innovative solutions to increase the system energy efficiency. Dealing with the class of intervention related to the power-train, the design activities of a propulsive device are presented in the present work, designated to propel the ship or to recover energy when it is sailing. The Velettrica SAIL-POD device is characterized by an innovative variable blade-pitch mechanism, aimed at allowing the device to work properly under different operating conditions and tailored to the hull characteristics. The propeller design is driven by the need of high level of thrust when the device is operating in propulsive mode, low resistance when operating in regenerative mode and enhanced efficiency over the whole operativity. Accordingly, the design process has been directed towards high propeller diameter, symmetric blade section profiles, low values of expanded area/ratio and a limited excursion of blade pitch, while the design operating condition suggested low propeller rate of revolution. To comply with the above-mentioned needs, a patented mechanism has been expressly designed to regulate the blade folding kinematics together with the blade pitch excursion, whereas composite materials have been investigated to ensure blade strength and reduced weight. The power chain, consisting of a power control unit and the energy storage system, has been defined together to a dedicated Permanent Magnet motor exploiting a prescribed torque range. An extensive experimental campaign has been performed at the CNR-INM towing tank to address the SAIL-POD propulsive/regenerative performance in calm water for different operating conditions. A digital tool for propeller sizing, combining propeller performance and hull and engine characteristics, has been applied to identify the optimal propulsive and regenerative performances. Results represent the proof of concept, in laboratory environment, of the innovative propulsive system as well as the usefulness of the adoption of digital tools to enhance the ship performances during the service. The analysis of propulsive performances under open water conditions highlights the areas of intervention for further developments of SAIL-POD.