The 2017 America’s Cup may be won or lost on foil design. With a lower wind limit of six knots, it will be crucial to get up on the foils at low speeds. To foil at low speeds, all the teams have built foils that are longer, skinnier, more flexible and harder to control. At high speeds, cavitation increases drag and decreases stability. Straight line top speed, manoeuvrability and stability all needed to be traded off against each other. This video does an excellent job of explaining the design issues. Remember that Nick Holroyd was the head of design at Emirates Team New Zealand for the 2013 America’s Cup and led the work that gave ETNZ the breakthrough to fly their AC72 on hydrofoils.