Basic Design and Virtual Prototyping of a Hydrofoil Hybrid Daysailer

The paper presents a preliminary design activity and virtual prototyping of an innovative boat equipped with hydrofoils and hybrid propulsion, with the aim of extending the foil technology from the field of competition boats to recreational day-cruiser yachts and create a craft with minimal environmental impact. Over the last decade, the nautical world has seen an increased use of hydrofoils, which allow boats to rise from the water, greatly reducing resistance to advance and increasing performance. In particular, this work dealt with the preliminary design of a day cruiser sailboat with foil technology and hybrid propulsion that allows to combine green and comfortable navigation both under sail and motor and that, when required, can sail in a more performing way by exploiting the foil technology and the thrust of the wind. The design process began with an in-depth study of the state of the art, evaluating advantages and disadvantages of the projects already built and functioning, identifying the crucial points to be respected in the design phase. After having deepened the theory and physics of sailing on foils, a MATLAB code was created to integrate all the stability equations that characterize hydrofoil sailboats, connecting the acting forces and allowing to define the dimensions of the geometries. The MATLAB code was also fundamental in speeding up the computation phase in the later stages of the iterative preliminary design process. At this point, the first freehand sketches were made which integrated the basic design of the hull lines and the functions necessary for the flight of the boat. The next step was to model the geometry of the hull and the appendages in the CAD environment and, subsequently, the wing movement mechanism so that it could both manage the incidence of the profiles and retract the foils when the boat is moored. Through the study of the state of the art of the foils already made and of the relative profiles, it was possible to identify the geometry of the hydrofoil and the type of profile that could satisfy the requirements in terms of thrust, stability and resistance to advance for correct foiling navigation of the boat. The chosen profiles were tested in the supposed operating regimes by means of dedicated simulation programs, obtaining the characteristic curves at the various speeds. The boat was subsequently placed in a virtual environment to be able to test its resistance to advance, its sailing behavior through VPP analysis and its stability as a function of weights and thrusts. In order to make the boat green, it was decided to install a hybrid type engine that could provide the propulsion necessary to bring the boat to the speed necessary for lifting and when the boat is sailing in the absence of wind. The batteries that power the hybrid engine have been positioned in strategic points, partially replacing the ballast that provides the righting moment. To verify the behavior and the thrust generated by the appendages, a CFD study was carried out: it made possible to verify the performance and thrust generated by the designed hydrofoils, to return to the CAD environment to improve the geometries and to verify the interaction between the various surfaces while the boat navigates in full foil mode. A first scale model was printed by means of additive manufacturing techniques, exploiting these ones in the creation of scale models for the simulations in the naval tank, as well as for aesthetic-functional evaluations. Future developments include detailed design and physical prototyping of a first boat for water testing.