Super simple and super efficient, the ACCWing holds great promise for a wide range of watercraft
There have been many attempts at popularising wing sails but few are as simple or efficient as this design. The ACCWing system consists of a fixed, free standing carbon mast around which a soft wingsail rotates.
What makes it stand out among other simple wing sails is the ability to easily induce camber to create a super-efficient shape that differs on each side of the wing, in a similar manner to an aircraft wing. This creates a huge amount of additional lift compared to wingsails that are symmetrical each side.
‘You can easily feel the extra power when we flex the wing by inducing camber,’ says ACCWing’s CEO Philippe Marcovich. ‘It makes a big difference to performance in light and medium winds.’ Camber is induced simply by pumping compressed air into “muscles” made of thin silicone tubing on each side of the sail. This shortens the tubes, changing the sail profile by creating a concave shape on the windward side and a convex shape on the leeward side of the aerofoil. It’s an amazingly neat idea!
The pressure in each muscle is controlled separately, via remote control, which gives instant and precise control of both twist and camber. The tubing is very thin and very little air is used, so there’s no big power draw even if an electric compressor is needed. On the 56m2 prototype rig the compressed air is supplied by a dive bottle, which works for a week of day sailing.
Tacking is easy, with no violent motion, flogging sails or excess noise. The balance area ahead of the mast makes gybes gentle and smooth, even in heavy weather. Before tacking or gybing neutral camber is selected, then after completing the manoeuvre the camber and twist for the new tack is dialled in via the control panel.
Wings intended for a yacht are typically made of the lightweight laminates more usually employed for code zero sails. Unlike conventional sails these are flat panels and don’t need to be designed with a complex three-dimensional shape, which helps keep costs in check.
A second generation prototype has been installed on a full size 56m2 wing fitted to a 17m tall mast on a 10m lightweight catamaran. This sail can be controlled by hand via a 4:1 purchase, even in true winds above 20kts, though a relatively powerful central winch is needed to achieve enough halyard tension to ensure the fabric of the wing is pulled taut.
As this is a retrofit the mast needs to be stayed but compression loads are much lower than for a normal rig, partly because there’s no highly loaded forestay. Nevertheless, from the outset the ultimate vision is for unstayed rigs: a single mast for monohulls and one in each hull for catamarans. Running stays can also be added to enable code zeros and gennakers to be flown. An unstayed rig makes reefing very easy, even when sailing downwind, as the sheet can be released to allow the wing to feather on any point of sail.
The wing has a round nose that’s very difficult to stall and makes the sail very close winded – roughly 10° better than a conventional rig with quality sails, Marcovich claims. As well as the speed advantage, this resistance to stalling makes the ACCWing ideal for a novice at the helm and when steering on autopilot.
There are also three or four reinforcing battens that divide the sail into different panels, with reef points taken to the battens, avoiding the need to reinforce the fabric locally. The two trailing edges are independent, which helps the sail to adopt an efficient shape on each tack. A further benefit is that there are no mast tracks and therefore very little friction when hoisting, dropping or reefing the sail.
The prototype system was made in conjunction with sister company Sicomin, who formulated the epoxy infusion resins for the mast and helped evaluate the laminate used for the booms, including sample testing, to ensure they have an appropriate flex response. Sicomin GreenPoxy bio-based epoxy resins provided a more sustainable material solution for the hulls of the catamaran test platform with no compromise on performance.
Hughes de Turckheim, inventor of ACCWing and CTO, has spent a lifetime at the cutting edge of performance sailing, having started putting foils on boats some 50 years ago. As he points out, ‘Single-skin aerofoils were only used in aircraft for 30 years after the first successful flights. Yet in sailing we are still using them after thousands of years.’
The ACCWing is thus a welcome development that will make sailing easier and more efficient for the widest imaginable range of craft. The team’s currently working on the design of a 240 m2 wing for a 30m catamaran and is developing a 100 per cent composite telescopic version for merchant shipping.
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