Left: the tidy new F50 wheel is a step forward from the piecemeal control arrangements on most AC50s in Bermuda (Team New Zealand was the obvious exception, with flight responsibilities clearly delegated releasing Pete Burling to do his thing to devastating effect). Still a way to go (below) before matching the demands on F1 World Champion Lewis Hamilton with this complex Mercedes wheel; we also doubt the cotter pin that keeps the F50 wheel attached would impress a driver used to lumping 95kg+ onto the brake pedal at 220mph. Above: righting moment drives everything relating to control of a sailboat, even one as nimble as an F50 foiling cat. Look beneath the thin carbon skins and gossamer-covered wing and there are some big pieces keeping an F50 going
the media checks and tests, then leaving it all idling on the mooring for a couple of hours, then one hour of tuning-up, then through the competition period to being safely back on the dock.’
The result is that to power them through the day three 140 amp/hour 25v military batteries, weighing around 58kg, have been fitted to each boat. Despite this and the increased weight of the new foils (ironically enabling them to be built thinner) the sailing weight of the F50 is expected to be nearly identical to the AC50’s 2,332kg minimum, thanks to shedding most of the manual hydraulic systems and carrying one less crew. Given that the hydraulics are powered, it is perhaps surprising that the hydraulic accumulators, one of the breakthrough features of the AC50s, need to be retained. According to Holroyd they are still vital: ‘An accumulator gives you a very high instantaneous flow rate or a higher peak power output. So if you are trying to drive a daggerboard down in 0.5 seconds you can accumulate 8-10 seconds’ worth of pump power in the accumulator and release that again in 0.5 seconds. It also allows us to make the pumps and batteries a lot lighter, because you can design the pump to meet the average power consumption and use the accumulator to manage the peaks.’
38 SEAHORSE
Battery, rather than human-powered, hydraulics will transform the way the boats sail. As Drummond observes: ‘Humans are quite puny really compared to a battery. ‘There is a difference between “automa- tion” and “power-drive”: driving things with battery power will speed them up and also make them more reliable. That means we can race the boats at a higher level and ultimately make them safer, and not run- ning out of hydraulic pressure as you saw sometimes during the last two Cups… ‘We’ve done some simulation on how many tacks can be made in a short space of time and I don’t really think there will be any limitation from the battery power in terms of throwing the boat around. With six boats on the track you can certainly imagine it being quite an advantage not being limited by your power in terms of the available tactical options.’
The powered system in turn will make the F50’s response more predictable, says Holroyd: ‘Given how fast the boats are and the new fleet racing format, that is pretty high on your list.’
While Coutts has cited a top speed of 54kt (as opposed to the AC50’s 47kt), Holroyd reckons the jump from AC50 to F50 represents a 10-15 per cent perfor- mance gain across the board. ‘They really aren’t the same boats they were. Just simple things like being able to measure the speed at which the boards are dropping, and have the systems control that descent speed so the manoeuvring is a bit more pre- dictable than it was. Before, those systems couldn’t benefit from that feedback. ‘All we have really tried to do on the control side is to make things more consis- tent. Obviously lift varies as the square of speed… if you change the rake of the board by 1° at 20kt, then the lift changes by 250kg. If you change the rake of the board by 1° at 50kt, then the lift changes by 1,500kg, ie 50 per cent of the sailing weight of the boat.
‘Simply by being able to feed boat speed back into the control system we can dial
the sensitivity of it down with increasing boat speed. Then when you put a click on the twist grip on the wheel we can make it a consistent change in vertical acceleration or a consistent change in the percentage of the boat weight you are lifting… regardless of speed. That is how we can help the guys sail the boats better and smoother.’ Holroyd observes that most of the tech to achieve such functions was already on the AC50s but its use wasn’t permitted. ‘You have thousands of lines of computer code running onboard, yet previously you were stopped from using them.’ All that said, considerable thought has gone into avoiding over-automation. Take tacking, for example: ‘When you go to tack the skipper will first press a button that will unstow the weather board, because it is secured slightly canted with the top outwards to bring the foil itself right up and clear of the water,’ says Drummond.
‘So the board will now go into the more vertical position ready for dropping. When he presses the button again it will lower quite rapidly and drop into a lock. ‘Also during a tack the rudder elevator rake automatically swaps so the upward and downward forces from the leeward and windward elevators swap over. Plus the board’s drop rate is controlled through software, so as not to overload the elbow on the board and so it doesn’t bounce off the water surface or anything like that. ‘So the mundane aspects of a tack are fairly automatic, as in there is no sailing skill required in unstowing the board or dropping it. But there will still be some interesting judgement and just plain repeti- tive practice required for crews to drop at the right rate, to turn the boat at the right rate, to pop the wing camber through at the right time.’
The first F50 was launched mid- October in Warkworth, New Zealand with Core Builders Composites aiming to then launch the remaining five boats at two-week intervals.
q
CHRIS CAMERON
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