The America’s Cup school of foiling controls is the most widely known, but not necessarily the most advanced. Most readers of Seahorse know that Emirates Team New Zealand cleverly developed the workaround that enabled foiling in spite of the limits imposed by the AC72 Class Rule. Many know that Oracle found their own workaround to use a simple mechanical feedback link to enable precise control of daggerboard rake. Both workarounds provoked controversy - this is after all the America’s Cup. After ETNZ unwisely tipped their hand by showing off in Auckland, some leading designers pooh-poohed the benefits of foiling an AC72, insisting that skimming would give better performance all the way around the race track. And, during the Match, some Antipodean media feigned outrage, claiming that Oracle had a secret, computer-controlled, gyro-stabilized foil control system even though it was analogous to and about as sophisticated as the float that shuts off the water when a toilet tank has refilled.

We’ll look at other schools of foiling thought later in this article. For now, let’s look at how the America’s Cup boys design foils and their control systems.

The AC72 Class Rule, the now-abandoned AC62 Class Rule and the current AC Class Rule all prohibit movable control surfaces on daggerboards. The workaround comes from mounting the daggerboard cases on bearings to allow the entire board to be raked or canted. Yaw control has been ruled out for the 2017 AC but in 2013 ETNZ and their sister ship Luna Rossa both had control over all three rotations on their AC72’s. Additionally, leeway coupled dihedral foils self regulate and provide heave control. Roughly stated, as the boat rises higher, less of the daggerboard’s “vertical” section is immersed and leeway increases. The vector addition of leeway and forward motion then decreases lift from the “horizontal” section. It’s a bit more complicated than that, but that’s the basic idea.

In 2007, the clever string drop systems for the spinnakers (remember those?) of the lead mine AC Class were hidden beneath the foredeck. In 2017, some of the most clever design work of the foiling AC Class will also be hidden from sight - the daggerboard control systems. The current rule allows energy generated by the grinders to be stored in hydraulic accumulators: two for raising and lowering the boards, and one for raking the boards. For all other adjustments - daggerboard cant, wing trim, jib trim and rudder rake - the grinders must turn the handles. The rule writers reduced the wiggle room for control system rule interpretation: unless a control technique is explicitly allowed, it is forbidden. In 2013, Oracle interpreted the “position” of a valve to mean its position in space, rather than its open/closed position. By mounting the valve on the movable daggerboard case, the Oracle system used the valve’s position to close it once the board had moved the desired amount. The current rule eliminates this ambiguity about the word “position” but then explicitly allows systems to use positional feedback for daggerboard rake control. One thing that remains unrestricted is the number of gauges and readouts. The crew must trim the jib, wing and foils manually, but they can have as many dials and displays as they can process while grinding constantly and blasting around at over 30 knots. Oh, and while making tactical decisions at the same time.

Andy Rice’s three-part “Lateral Question” series with Kevin Ellway and Alan Smith in Seahorse August, October and November 2015 calls into question the entire AC school of thought on foiling and foil controls. Ellway and Smith believe that wand controlled flaps (elevators) on T-foils provide more stability and safety, and they have mathematical models and experimental data to bolster their case. That series leave unanswered the question of whether wand and flap systems can be scaled up to cats longer than 20 feet. Why not? Both the Antonov 225 heavy payload transport and the SR-71 Blackbird used hydro-mechanical flight controls. The offshore school was probably inspired by maths as well as surrealism when VPLP put “Dali moustache foils” on their latest IMOCA 60’s. Hugh Wellbourn might question whether that inspiration came from his Dynamic Stability System, which was used with great success on Wild Oats. François Gabart is leading the charge towards possible offshore full foiling with the new Ultime class. Foiling 100 foot long multihulls racing singlehanded around the planet in 2019 may make 49 foot AC Class yachts look timid in comparison. And no one seems to be exploring Paul Larsen’s use of Bernard Smith’s stability concept on Sailrocket2 to post 65.45 knots way back in 2012. No one except Larsen and Malcolm Barnsley, that is. Stand by - the best is yet to come.