Streamlines around an AC45 wing sail Streamlines around an AC45 wing sail

Rigid Wing Sails

The decision to use rigid wing sails for the next generation of America's Cup boats has lead to a race in understanding of this novel sail boat system. The AC45 and AC72 will be fast, light and exciting, and offer a unique challenge to both the sailors and the designers.

While experience with wing sails has been gained in the smaller c-class wing sail boats, Computational Fluid Dynamical modelling of wing sails can aid in the understanding of the complex interaction between the multi-element rigid wing sails and the conventional flexible foresail. Areas of interest in wing sail design are the aerodynamic profile of each element, the gap between the leading and trailing edges and the optimal angles of attack for each element at each position of sailing. Determining these qualities, as well as the spanwise lift distribution of the wings, can be key to a successful design.

The key to rapid optimisation and development of complex systems is the design of a robust and flexible computer model. For this work an AC45 boat was designed and modelled using Rhino and it's parametrisation system Grasshopper. Using these tools, changing variables such as each elements angle of attack, element gap, element profile, choice of gib or genoa, heel and apparent wind angle are simple. The geometries are then exported to a geometric file and used in the OpenFOAM simulation. Optimisation studies can then be carried out testing for a range of design variables.

The Rhino and Grasshopper files for the above video are freely available upon request. Please email

See the Conventional Sails section for addition information.