However, there are significant drawbacks to the rigid wings like those used on the AC72’s – not so much on the water as off. They are large and fragile and require a significant infrastructure for rigging and unrigging. Large shore teams are required, as is a large ground area. Furthermore, leaving the boats in the water is not practical. All of this contributes to a significant increase in the cost of mounting a campaign.
But we don’t want to go away from the sort of performances that we saw in the 34th America’s Cup – boats approaching 3 times wind speed and foiling upwind at nearly 30 knots and downwind at nearly 50.
Soft wing sails may offer an elegant solution and provide a means of keeping costs down. Soft wing sails may capable of producing similar sorts of performance to rigid wings. Much of the performance advantage of rigid wings comes from the multiple element design. Multiple element wings can carry high camber due to the re-energisation of the boundary layer part way along the leeward surface of the wing which delays trailing edge separation. These increased cambers result in higher lift generation.
We know single element soft wings are capable of generating good lift and drag characteristics. Multi-element soft wings have not really been explored but are certainly possible. I have penned conceptual designs which, at least in the preliminary modelling, show great promise of approaching rigid wing performance. We are really at the beginning of the technology curve for soft wings and there are significant design and performance improvements waiting to happen.
Such technological development is also very likely to trickle down into more common usage. Soft wings with reefing and stowing ability could find application in many types of sailing craft. So like in Formula 1 car racing, where we see engine improvements, regenerative braking and other such technologies cascading down to everyday motoring, we could see AC technology influencing future yacht design.
This is likely to have an influence on the interest in the sport as yachties will see an increased relevance to their sailing.
Greg Johnston – Advanced Wing Systems