At first glance, the America’s Cup teams’ AC50s may look similar, but out of sight within the hulls and under the water lie significant differences in foil designs and control systems. The margins to be found in these will be key to winning (or losing) the Cup.

Nick Holroyd is technical director of SoftBank Team Japan, a design pioneer who previously worked as technical director at Emirates Team New Zealand on NZL2 and NZL5, the first foiling AC72 catamarans. He explains: “This is a very, very long way from a one-design environment. It really is a full development class. Having the hulls and cross structure etc as one-design is, from my point of view, a benefit as it lets you focus on the stuff that makes you go fast.”

In this podcast he tells us much more about what foils are allowed, the upgrades and modifications that will probably be done to the bitter end – and how – and why teams may be trying to accomplish different objectives.

Since foils were first introduced to America’s Cup racing in San Francisco in 2013, the advances made in foil design and efficiency have been startling. Looking back now, Holroyd says: “That was a once-in-a-generation Wild West of yacht design. It was very hard to keep velocity prediction tools up with our state of development. So the mathematics behind it were relatively crude and because those mathematical models of the boa were lagging we didn’t have much ability to optimise.”

Four years on, design tools have been defined and developed that give teams a more much accurate prediction of the behaviour of the boats and allow teams to optimise performance. So not only are the AC50s significantly faster than were the AC72s, but they fly on foils far earlier in the wind range, at 7-8 knots true.

Nick Holroyd, technical director SoftBank Team Japan

Under the current protocol, the boats race between 6 and 25 knots of wind. Once the breeze lifts off the bottom end of the wind range, everything changes quickly – power, loads, stability.  At 6 knots the boats are in displacement mode and slow (though winds this low are very unlikely in Bermuda in May and June). With only half a knot more wind speed, they are fully foiling and boatspeeds surge from 7 knots to 12 knots.

At 7-8 knots TWS, these boats are foiling downwind and, with a little more, foiling upwind too and flying right around the course without touching down, including through tacks.