Yacht sail systems are subjected to low speed and transitional flow. Because of the supporting structure (mast and boom) of the sail system and the curvature of sail membrane, sail systems also have a partially separated flow. In this work, it is introduced the sectional method as a sail system flow analysis tool. The sectional method uses the surface discretization and it is based in the simultaneous approach for viscous-inviscid interaction but, it works independently to the initial panel mesh and inviscid panel method calculation, permitting the adjustment of sectional points to have a better local convergence. The sectional method is applied to the detection of separated flow regions by means of integral boundary layer parameters investigation. The investigation is used in cases of weak separation and strong separation, when analysing mast and sail configurations. The weak separation detection is applied to a three-dimensional sail shape in a sail design problem: the study of parameters such as twist and section curvature in order to control separation on the sail.

The development of modern sailing boats has been based almost entirely on the cooperative efforts of enthusiastic skippers, designers and sail-makers, with very little contribution from scientists and technologists and using just basic scientific principles. In recent times, urgent and strong requests for improved performance, mostly for racing yachts, have guided the interest and the attention of the scientific community in the optimisation of sail performance and design approach. Sailing performance depends on the sailboat velocity, aerodynamic and hydrodynamic characteristics. This thesis focuses on the importance of the quantitative evaluation of the sail loads and how this contributes to the improvement of the performance of a sailboat through the development of a system for aiding sail design and assisting mast design. The objective of this study is to provide an integrated design system, which supplies analysis method and design features via a user-friendly graphical interface of a single-sail configuration. The major achievement is the development of an integrating numerical method, which evaluates loads and their distribution and the consequent deformed sail-shape. It improves sail performance analyses and design of new sails. Summarising, the major achievements are: • efficacy of accurate performance analysis for each sail, for any given shape over all the possible sailing courses; • critical investigation of the sail behaviour in the above-mentioned cases; improved approach to an integrated sail design; improvements in mast design from the structural and aerodynamic point of view; limited design costs, in terms of time consumed and computational power employed; efficacy of the visualisation of novel designed sail and predicted performance, which reduces the number of possible design flaws. hi conclusion, the integrated sail analysis and design system presented has important margins of improvements and diversification: extensions to non-homogeneous and anisotropic sailcloth, to two-sail configuration, windsurfs and integration of the mast.