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.
When foiling, the hulls often appear to have a “nose-down” attitude, which seems to be the wrong way to go with the possibility of the bows digging into the water. Is this a way off changing the angle of attack of the wingsail? Clearly the attitude of the hulls is controllable by modifying the angles of attack of the main foils and the rudder foils, so it must have an advantage of some sort?
Hi Duane, the nose down attitude reduces drag two ways: less of the rudder is in the water, so less hydro drag. The bowsprit structure point about 2.5° up when the AC Class cat is in a neutral fore-aft attitude. By sailing nose down aero drag is reduced.
Really good video!
please post more of them like that
Excellent interview, Nick did a great job explaining the mysteries of foiling
Yes, Nick is not only a good designer, he’s good at explaining things, too!