AC72 Foil Control Secrets:

By Jack Griffin

Some people have questioned whether Oracle Team USA had a secret (and illegal) foil control system in their AC72 that helped them defend the America's Cup.

OTUSA has released drawings and photos of their system, which used a simple "mechanical feedback" loop to allow precise control of the daggerboard rake. Helmsman Jimmy Spithill had buttons on the wheel to rake the daggerboard fore and aft in precise increments of 0.5° giving him better control over lift for hydrofoiling.

OTUSA designers Dimitri Despierres (mechanical systems) and Eduardo Aldaz Carroll (electronic systems) began work in late June 2013 to help the team gybe better. The goal was to reduce distance lost in a gybe from 150 meters to 30 meters. To do this the engineers needed to deal with the problem that board movement varied depending on hydraulic pressure, making it impossible to control lift. What they needed was a way to move the board a fixed amount independent of the pressure and drag load on the board. Within a month, mechanical engineer Alex Davis developed a test bench with a servo control, hydraulic valve and hydraulic ram to simulate movement of the daggerboard box (see photo below).

Once the test bed system worked, the system was tested on board. Accuracy was fine, but it reacted too slowly. Mechanical engineer Neil Wilkinson and hydraulics specialist Rolf Engelberts improved the system to improve response speed and make everything more reliable and robust.

AC72 daggerboard controls on OTUSA Boat 1

The hydraulic ram for rake is not visible in the photo below, but you can see the rams for board cant, as well as the daggerboard cage and daggerboard box. The box moves within the cage, which is fixed in the hull.

Rendering of AC72 daggerboard cage below. The cage is fixed in the hull. The daggerboard box moves fore / aft (rake) and side-to-side (cant) within the cage.

Controversy and protest by Team New Zealand

OTUSA wanted to make sure their system complied with the AC72 Class Rule. They filed a "Public Inquiry" to the Measurement Committee and got approval on 8 August 2013 - only a month before the America's Cup Match was to begin. Team New Zealand then tried to have OTUSA's system ruled illegal but the Measurement Committee stood by their initial decision and the International Jury ruled that New Zealand's protest was made too late, but would not have succeeded even if it had been filed on time. The marked up schematic below was part of Team New Zealand's submission. OTUSA eliminated the spring labeled "Component X" making the TNZ protest moot.