A relatively new phenomenon within the sailing world is the use of hydrofoils to boost sailing performance. This technique is applied to a wide range of boats, from dinghies to ocean racers. An interesting question is whether one of the slowest racing boats in the world, the Optimist dinghy, can foil, and if so, at what minimum wind speed. The present paper presents a comprehensive design campaign to answer the two questions. The campaign includes a newly developed Velocity Prediction Program (VPP) for foiling/non-foiling conditions, a wind tunnel test of sail aerodynamics, a towing tank test of hull hydrodynamics and a large number of numerical predictions of foil characteristics. An optimum foil configuration is developed and towing tank tested with satisfactory results. The final proof of the concept is a successful on the water test with stable foiling at a speed of 12 knots.

The paper presents an overview of a joint project developed among Politecnico di Milano, CSEM and North Sails, aiming at developing a new sail pressure measurement system based on MEMS sensors (an excellent compromise between size, performance, costs and operational conditions) and pressure strips and pads technology. These devices were designed and produced to give differential measurement between the leeward and windward side of the sails. The project has been developed within the Lecco Innovation Hub Sailing Yacht Lab, a 10 m length sailing dynamometer which intend to be the reference contemporary full scale measurement device in the sailing yacht engineering research field, to enhance the insight of sail steady and unsteady aerodynamics [1]. The pressure system is described in details as well as the data acquisition process and system metrological validation is provided; furthermore, some results obtained during a wind tunnel campaign carried out at Politecnico di Milano Wind Tunnel, as a benchmark of the whole measuring system for future full scale application, are reported and discussed in details. Moreover, the system configuration for full scale testing, which is still under development, is also described.

This paper presents new results obtained from analysing on-the-water pressure, shape, force, speed and direction data that were obtained from experiments in the Hauraki Gulf in Auckland, New Zealand in April 2014. A fully instrumented Stewart 34 Class yacht sailing downwind was used for the tests. Details of the analysis of the results from simultaneous time-resolved measurements of pressure, sail shape and loads are presented. The dynamic behaviour of the fluid-structure system made up of a light sail cloth and highly curved flow is investigated. Aerodynamic forces on the asymmetric spinnaker are determined from the combination of point pressure measurements across the sail with simultaneous shape measurements. Simultaneous time histories show a strong correlation between the variations of pressure distributions, flapping sail shape and the forces at the corners. Periodic curling and filling of the spinnaker luff influences suctions, in particular at the leading edge, and forces, which can dynamically change on the order of 40- 50%. The results are similar to, and extend, those that were presented by the authors at the 2013 Innov’sail Conference in Lorient, France. It is expected that the results from this work will give reliable benchmark data which may be used to validate unsteady fluidstructure interaction numerical simulations of downwind sails.