Technology
(Don’t) shake it all
about
The theory of vortex shedding is well known to golfers with their little dimples (the balls, that is!) It was also toyed with in the past by 12 Metre sparmakers... so why not extend the benefits to the rigging itself?
The parentage of Future Fibres’ latest answer to high-tech composite rigging, becomes quite clear when you start looking at how AEROsix is put together. An extended elliptical aerofoil shape, AEROsix takes the best elements of Future Fibres’ multistrand carbon rigging, ECsix, and combines it with RAZR, Future Fibres’ solid carbon product. Each of AEROsix’s parents could claim great advantages over what came before them. But while these products have become established as the go-to choices in the market place, Future Fibres asked itself, what next? In the May edition of Seahorse, p72-73, we looked at the reasons why the company felt it was time to develop and launch AEROsix into the market.
However, things have moved on apace even in the past few months as Future Fibres has conducted more research in conjunction with the Wolfson Unit at the University of Southampton. Some interesting and somewhat unforeseen discoveries have emerged out of the R&D work at the Wolfson Unit, as R&D manager at Future Fibres Jonathan Duval explains: ‘You might think that a smooth surface on your rigging is better aerodynamically than a rougher, braided surface such as we have with EC6 and now AEROsix. ‘However, we have discovered that not only does a rough or braided surface have a significant effect in dissipating any vibration, but it also helps with the flow. If you think about a golf ball, the surface isn’t smooth but has those multiple dimples. By creating forced
80 SEAHORSE
turbulence, you reduce the vortex shedding at the back of the rigging, and so you bring the laminar flow back together more quickly compared with smooth rigging.’ Duval concedes that a smooth finish is better on the forward-facing surface. ‘The trouble is, the air flow gets very, very disturbed on the back of the rigging, and the disruption of laminar flow far outweighs any small gain made on the front face of the rigging.’
The initial driver of AEROsix was to create a high performance rigging option with a more aerodynamic profile compared with round or even aerofoil-profile rigging. As the previous article explained in detail, the results of wind tunnel research at the University of Auckland and VPP modelling by Future Fibres and North Design confirmed a significant benefit of the 2.7:1 extended ellipse profiled rigging over both 2:1 elliptical rigging and the round- section rod. For a typical-length day race at a superyacht regatta, the gain translated to a theoretical 19-second advantage. For a two-day offshore race like the Caribbean 600, the difference could add up to as much as 12 minutes.
However, the side benefits of AEROsix have started to look as interesting as the aero gain, with both the reduction in vibration and drag providing big advantages. As yacht designer Juan Kouyoumdjian points out: ‘I have been working on the development of a 125ft high performance boat where we are looking for performance gains wherever they can be found. We saw
Above: this graphic
visualisation from Future Fibresʼ extensive VPP studies shows why the drag
forces acting on leeward rigging are a more important concern than drag on the windward rigging. As illustrated clearly in the graphic, the wind tunnel effect of the sails and the slot between them results in much faster (and potentially more
turbulent) airflow on the leeward side of the rig than on the wind- ward side
very early on that the potential of AEROsix was worth investigating. The aerodynamics were certainly important, but the potential benefits of reduction in vibration were also very interesting to me. You start to realise the drag related to vibration is as important, if not more so, as anything you can do with the aerodynamic alignment of the rigging. Therefore the drag reductions one can expect from this lack of vibration could be substantial, not to mention the comfort factor because of the whole boat not receiving this noise that comes from the rig. That’s where I see the most substantial gains in performance.’
Danny Gallichan, skipper of the Wallycento Magic Carpet 3, has almost one year’s experience with AEROsix installed on the boat earlier in the 2018 season. He has been delighted with the lack of vibration, particularly when sitting stationary in the marina or at anchor. ‘We’ve sat through quite a bit of different wind, we've sat in Porto Cervo with quite a lot of Mistral conditions and I haven't seen any of the vibration that was a concern originally. I think ellipse is better than aerofoil and it actually seems better than the more traditional round rigging.’ Duval says that such is the amount of vibration generated by some forms of round rigging, it’s virtually equivalent to having two rods mounted side by side. Elliptical rigging smooths out the vibration to the point where it’s virtually undetectable whether the boat is in motion or stationary.
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