Update
Our Argentinean photographer friend Matias Capizzano just keeps on doing it, putting together sailing images that can stop you in your tracks while often using the simplest of
subjects.This photo was taken at the South American Optimist championships in August, though rarely for Seahorse this one is about the image and not really about the racing
MANY SCHOOLS OF THOUGHT – Jack Griffin
The America’s Cup school of foiling controls is the most widely known, but not necessarily the most advanced. Nor is it the best understood.
Most readers of Seahorse know that nearly four years ago Emirates Team New Zealand cleverly developed the workaround that enabled foiling in spite of the limits imposed by the AC72 class rule. Many also know that Oracle found their own workaround, using 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 racetrack. And then, during the Match, some of the Antipodean media feigned outrage, claiming that Oracle had a secret, computer-controlled, gyro-stabilised foil control system…
The reality was that the Oracle system was analogous to and about as sophisticated as the float that shuts off the water when your toilet tank has refilled.
We’ll look at other schools of foiling, though, later in this article. For now, let’s look at how the America’s Cup boys design their foils and their control systems.
The AC72 class rule, the now-abandoned AC62 class rule and the current AC rule all prohibit movable control surfaces on dagger boards. So the workaround now comes from mounting the
10 SEAHORSE
daggerboard cases – or cassettes – 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 sistership Luna Rossaboth had control over all three rotations on their AC72s. 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. For all other adjustments –- daggerboard cant, wing trim, jib trim, rudder rake – grinders must turn the handles. The rule writers also reduced the wriggle 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 by the desired amount. The current rule eliminates this ambiguity about the word ‘position’, but then explicitly allows dagger - board systems to use similar positional feedback for rake control.
MATIAS CAPIZZANO
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