The objective of this research is to explore the possibility of using Passive Adaptive Composite (PAC) on structures to help control the lift generated by hydrofoils on boats such as the International Moth. Intorducing composite fibres oriented at off-principal axis angles, allow a foil to passively control its pitch angle to reduce the lift generated at higher boat speeds helping to achieve a stable flight in a wide range of weather conditions. PAC utilises the inherent flexibility of a composite structure to induce a twist response under bending load which could be used to minimise the use of active control systems, or even improve the dynamic response of foils in waves. However, to design flexible foils requires numerical and experimental tools to assess the complex fluid structure interactions involved. This paper eveluates a simplified hydrofoil geometry designed to reduce its lift coefficient with increased flow speed. A coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) methodology is presented to predict flexible foil performance. Validation of these numerical tools is achieved through the use of wind tunnel experiments including full field deformation measurements. Twist deformations resulted in a reduction in the effective angle of attack by approximately 30% at higher flow speeds reducing the foil lift and drag significantly.

The development of a tool for predicting the dynamic performances of sailing yachts is presented in this paper. After establishing the equations of motion and the coordinate systems, the modeling of the various contributions to forces and moments of such a mechanical system is presented. These contributions are estimated making use of empirical formulas available in literature. Then the development of the graphical user interface is described, which allows a friendly approach to the solution of various problems, like for example the analysis of a tacking or gybing maneuver, or the study of the behavior in gusty wind. Some preliminary results are shown, for the case of a 37’ IMS racing yacht. They describe validation tests on steady course and round circle, then a tacking maneuver, and finally straight course sailing in gusty wind. They are compared, when possible, with experimental data. As last example, the tool is used in the context of a more sophisticated application, where it is embedded within an automatic optimization loop, aimed at finding the best rudder history during a tack. It is demonstrated how the optimization gives a significant result in terms of boat performance.