Technology
Life at 80 RPM...
Smooth and consistent power delivery from the grinders is the key to keeping your AC75 aloft... and that took a bit of a Harken rethink
Have you noticed something different about the way the AC75 grinders are working their pedestals? It’s not what you see in the videos (if you catch a glimpse of them at all as they now practice their art low in their cockpits well out of the airstream); it’s what you don’t. You’ll never see any of the grinders pause, shake their handles or reverse direction when changing gear. Instead they just keep going at a constant cadence, maintaining the optimal 80rpm. The new technology that enables them to do this – a game-changing innovation by Harken called True-Clutch – has been on the AC75s for more than a year but until now it’s been kept strictly secret. For a very long time, pedestal systems on sailing yachts have relied on ‘dog clutches’ that activate by manually engaging sets of teeth to shift from one gear or function to another. The dog clutch mechanism can be activated in various ways with a button, lever or switch, or with the grinder handles themselves, but whichever way it’s done the whole team of grinders has to stop working while the clutch is engaged, which inevitably results in a loss of efficiency. Generations of sailors just accepted it, even in the highest echelons of the sport. But with the advent of large, fully foiling raceboats it quickly became a very big deal.
66 SEAHORSE
‘Once the boats started flying, almost everything changed,’ says Mark Wiss, director of Harken’s global grand prix and custom yacht team. ‘On the AC50s the grinders never stopped. They had to keep the oil constantly moving and that pause was a real problem. The grinders lost momentum, it slowed them down and stopped the flow of oil.’ The output of each pedestal drives a far wider range of functions than ever before: mainsheet and traveller, jib sheets, barber haulers, runners, main and jib cunninghams, mainsail outhaul, foil and rudder wing flaps, code sail halyards and more. Trimmers’ reaction times have to be a whole lot quicker and while they’re at it the flight controller is relying on power from the same source, at the same time. With all of this going on, the power from the grinder pedestal must be shifted between functions and gears much more frequently – perhaps a dozen times during one 90-second gybe – and when every shift requires a pause, the boat becomes much harder to sail. ‘True-Clutch was originally developed towards the end of the 35th Cup cycle in Bermuda,’ Wiss recalls. ‘Oracle came to us and said this is a real issue. The grinders had an optimum cadence that they wanted to preserve, at about 80rpm.
Above: nope, itʼs not a next generation superbike clutch; itʼs the all-carbon clutch from an AC75 grinder pedestal, which allows genuinely seamless
gear changes. Developed by Harken and refined into two new models for the current Americaʼs Cup cycle, Harken True- Clutch can handle more than 1,000Nm of torque and yet the whole assembly weighs just one kilo...
They’d speed up to 100, 120rpm at times but mostly they’d maintain that ideal speed.’
The pressure was on to design a solution – and deliver it fast. Harken assembled a crack team of engineering talent from its Italian and American operations to work alongside Oracle’s own in-house team, with Harken Italy’s chief engineer, Michele Cazzaro, taking the lead.‘ We couldn’t just steal a clutch solution from the automotive industry because there wasn’t anything suitable,’ says Harken engineer Ben Biddick, who was part of the design team. ‘Weight is less critical in those applications than it is for us, and we were working with a different range of torque. We have to start with what the human body can do and then tailor that into a transmission device.’
Several solutions were considered including a constant mesh gearbox but that was too heavy, too complex and a suitable one for a human- powered pedestal would have taken too long to design, test and build. Cazzaro’s elegantly simple bespoke solution for was more akin to a motorcycle clutch: a stack of friction plates and a spring-loaded pressure plate in a slim, lightweight housing. But unlike a motorbike clutch, which is activated manually,
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