Bermuda,’ Wiss continues. ‘The self-tacking 32mm CRX that is used on the AC40 is a three-car system, which is an updated version of that used on the AC50 catamaran. The self-tacking system eliminates the need for a trimmer on each side as there is no longer a need to release and pull the jib sheets. Instead, the jib sheeting is all down to a single sheet that is managed by a hydraulic cylinder. The sheet is set up like a Soling where the sheet goes between the clew and the cars before going forward to the bow and then back to a hydraulic cylinder. ‘Because the track is curved
there are three cars that are connected together because they need to go through the bend. If you have a long car, it doesn't travel around the curved surface. The mainsheet traveller system also runs on a curved track but it is far more complicated and was a specific area of development at Harken. We call it Flight Control.’ One of several key reasons that
set the AC75 and AC40 mainsheet tracks apart from others is the need to pump the mainsail to help get the boat up and onto its foils in light airs. Think windsurfing or Moth sailing and you’ll be creating the right mental image. Being first onto the foils and/or last to come off them presents a huge advantage so the incentive is there. But on a Cup boat the loads are extremely high. ‘In light weather, to start the
flight and then once they're flying you'll see that the traveller system is moving a lot. The cars that are moving at high speed and more importantly at high frequency. So unlike a keelboat where you pull the car up every once in a while in the lulls and drop it down in the gusts, here the car is moving all the time. It never stops. ‘It's being operated hydraulically
so the grinders or the cyclers are now having to push oil. Every time the carmoves it is using oil pressure that they are creating. So the real challenge was developing the bearings in the cars and the track to be very efficient, especially at high speed and high frequency, which is something that you don't usually do in sailing. One of the starting points for us was to optimise our traditional roller bearing cars to work with the new loads and frequency that were required for this flight control concept. ‘The track itself is a new shape
plus it pivots. And while a bend in the vertical plane like a smile isn’t new, now it's got to pivot fore and aft.’ But even then that’s not the end of the issues around movement that have to be catered for. ‘The mainsheet is a hydraulic cylinder
Above: Harken supplied all the traveller systems for the AC40s: mainsheet traveller cars on the left and the jib cars on the right of the photo. Right: a long single car won’t fit on the curved tracks for the AC boats’ self-tacking jibs, so several short cars are joined together. The upper part holds the sheave for the single jib sheet
that comes straight to the car,’ Wiss continues. ‘And this cylinder is positioned in between the two mainsail skins which in turn have another Flight Control pivoting track that's sewn on to the clew of the sail. ‘When you tack or gybe the boat
the two mainsails have to keep their correct depth by sliding past each other. These have to move and at the same time the traveller car is also moving constantly. Plus, it’s always at full working load. Unlike a normal keelboat where the load comes off, the car moves and the load comes back on again, aboard an AC75 or AC40 the sheet barely gets eased. ‘Putting all of these combinations
togethermeant that we had to work on updating and revising how we design the cars and the track to work at high speed, high frequency and always at working load. ‘To evaluate this we set up
various tests in HarkenLab where we investigated different bearing materials to make sure that they were efficient. After that and perhaps most importantly we put the designs through an endurance test where the cars travelled a total of 14km on the track to simulate 10 days of sailing. ‘Once again this is way beyond
what you’d expect for a normal racing keelboat.’ Interestingly, the company ruled out ceramic coatings for this application despite their popularity in other areas, especially winch drums. ‘Ceramic is a greatmaterial for some applications but not this one. Ceramic ball races are hard and brittle and they erode an aluminiumalloy track in no time.We experimented with a titaniumtrack which worked really well but thematerial is very hard to get in a long bar of the length we would need, is really expensive and takesmonths tomachine.’ In fact, striking out the idea of
using titanium has worked in favour of the new technology filtering through to other areas of the sport with a system that doesn’t rely on prohibitively expensive materials. ‘It’s still early days but it is clear
to us that the rate at which the performance world is developing outside the Cup means that Flight Control is going to be an important part of future designs. The Mark Mills-designed Flying Nikka is a good example and has our system on board. Plus, as is always the case with these big steps forward, solutions like these are never going back in the box!’
www.harken.com
❑ SEAHORSE 57
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