Above: one man who usually had already ‘thought of it like that’ was Ben Lexcen, designer of the 1983 Cup-winner Australia II. The Australian design maverick was putting wings on 18ft skiff rudders in the 1950s and would surely have taken in the technology on display in Bermuda without batting an eyelid. Outside the C-Class (inevitably) the importance of end plate effect on multihull rigs came to prominence during the 2013 Cup in San Francisco – Prada (below) and Team NZ were early to the table with this aero platform beneath the wing while Oracle went one step further by adding an under-deck pod to extend the effective rig span downwards. The AC50s feature a similar pod plus a horizontal ‘aero-screen’ sealing the foot of the headsail
easing your outhaul and sailing with the top of the sail almost luffing. It’s radical, it provides so many options and, as I have talked
about before, having many options is both good and bad. Good as you have all kinds of options to get it right but bad as sometimes too many options create the opportunity to get a bit lost – especially when any one simple decision can affect so many other parts and pieces on the boat. With an understanding of performance above the deck, next we’ll
move into the dynamics side of the America’s Cup rigs – tuning and trimming the foils above the deck. There is an optimum wing element shape and twist that all the
teams will have and by now will know well, a perfectly manufactured aero dynamic section. By contorting the wing you then make changes for certain wind conditions: high and slow mode, low and fast mode, reach mode, upwind mode, downwind mode, and so on. For most of the boats we all sail we accomplish the same thing
by adjusting the backstay, outhaul, vang, mast step and shroud tensions, which contort the sails and spars as we want. On a wing the principle is the same, while the method of getting a result could be radically different. The question remains: what is the methodology behind finding the holy grail of wing trim? Changing the shape running from the front to the back element
of the wing, and each of the aft three sections, moves not only the fore and aft centre of effort (or, in layman’s terms, the draft) but
also the vertical centre of effort. You can move it higher and lower depending on how you twist the back elements. The end plate of the entire platform, including the jib, also greatly
affects the vertical, as well as fore and aft, centre of effort. So all of a sudden there is a direct correlation between how you trim the jib and wing and how well your foils are working because that fore and aft balance created above the water directly affects how well the wings work below the water. By assessing the options for design, manufacture and on-the-
water trim we understand to a degree the amount of freedom teams have to optimise their boats. Remember, one of the other ‘non- one-design’ parts of the platform is the system that is used to move the wing around both as a unit and as individual parts. We can also start to appreciate the way all of the elements relate to each other, where a small tweak could spur a myriad adjustments with the system used to contort it, and how they in turn affect the balance and flow over the underwater foils. One of the trickledowns of this Cup cycle will certainly be the
software being developed to manage, create and run these programmes and these boats. No more is it a seat of the pants ‘ease-hike-trim’ that we all grew up with. Modern sailing, and the America’s Cup, left that concept in the dust a long long time ago. Ken Read is a two-time America’s Cup helmsman and the president of North Sails and will be commentating for AC TV in Bermuda q
SEAHORSE 25
GILLES MARTIN-RAGET
GRACE TROFA/PPL
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