News Around the World
whatever they have unless they had found an advantage that was worth pursuing.’ The underside treatments of the hulls are split into two distinct
camps. American Magic’s Defiant and Ineos Team UK’s Britannia both have smooth, flat undersides, while Emirates Team NZ’s Te Aihe (Dolphin) and Italy’s Luna Rossa both feature longitudinal bustles running down the centreline. Drummond prefaces his comments with the caveat that they are
based not on detailed analysis but first impressions from photo - graphs in the public domain. Looking at the New Zealand and Italian bustles, he believes they address different effects. They certainly look quite different, with the New Zealand version rounded and carrying volume along its length, while the Italian version reduces in volume moving aft becoming like a knife blade as it terminates in a distinct skeg just ahead of the rudder. ‘The New Zealand bustle has basically created the central hull
shape of a trimaran and then faired and extended it into the hull, so it complies with the volume distribution and stability rules of the class,’ Drummond says. ‘They have given a nod to low wetted area for better low-speed performance. ‘The Italian treatment is primarily for three-dimensional aero -
dynamic effect,’ Drummond believes. This is familiar territory for him because early versions of the Oracle AC72 catamaran had a similar but larger device underneath its centre pod. ‘The concept is that it extends the pressure differences from the sail plan (which produce driving force) down and under the hull, maximising the effective span of the rig and reducing induced drag.’ Foiling is, of course, the name of the game and the foil treatments
are again quite distinct. The three challenger yachts all feature torpedo-shaped bulbs with the wings extending out from the sides of the bulb, while the defender’s current wings spread directly from the tip of the foil arm, without a bulb. There is a ballast requirement in this area too and the speculation
is that the bulbs carry ballast and use carbon-fibre wings, while ETNZ may be achieving the ballast requirement using high-tensile steel wings, a method they adopted with their winning AC50 catamaran in Bermuda. ‘This could also be tied up with the rule where you can only replace a certain percentage of the weight of the foil,’ Drummond suggests. ‘If you have a lead bulb with carbon wings you can potentially replace more area.’ The number of wings and alterations are restricted under the rule. The other notable difference in the launch configurations was
that ETNZ and the British had different foils on either side, while the American and Italian teams appeared to start out with symmet- rical configurations. In test mode the asymmetric set-up obviously
26 SEAHORSE
pays because it provides instant comparisons between one concept and another. In Bermuda at least one team even raced at times with asymmetric foils, which was thought to be about maximising acceleration on the opening reaching leg to gain crucial control over the first mark rounding. Absorbing as it is to assess the shape and form of these yachts
as static pieces of sculpture, they perform in a dynamic high-speed world where they are subject to a fast-changing matrix of pressures and forces. The design headache is to solve a multitude of equations where all the factors – including flight, speed, acceleration, wind- speed, wind angle, heel angle, rudder angle, sail trim, foil settings – are constantly changing. Holroyd talks in terms of calculations in a virtual space of 10 to 12 dimensions. In the real world the sailors have to control and respond to this
constantly shifting, multi-dimensional array of forces with split second precision. Every small adjustment sets off a cascade of cause and effect that must be accommodated. ‘From the fine steering adjustments, to foil adjustments, changes in windspeed and trim, stretch of the sail, bend of the mast, everything is intimately linked,’ Drummond notes. These changes are at the most extreme in the transition between
displacement mode and flight, which is dramatic and fast. ‘You need to get those sails through a massive shape range and power range,’ says Team NZ mainsail trimmer Glenn Ashby. ‘It is like a truck with an 18-speed gearbox and you have to smash through the gears really fast.’ This is where the Cup will be won and lost, Lester believes. ‘We
are all transfixed on the hulls at the moment,’ he says. ‘The real deciders lie in the areas we can’t see: the operating systems and the hydraulics.’ If the external shapes are complex to build they are nothing like as complex as the internal workings, involving a maze of hydraulic plumbing and electronic connections. The double-luff mainsails also conceal a host of connections and devices for shaping the wing form. ‘The hydraulic power requirements of getting the boat around
the track are huge,’ says Ashby. ‘We have a certain amount of power and you can’t use it all at once, so you have to pick and choose pretty carefully what your next application will be. That choreography is fundamental. One bad gear change or wrong button push is going to be the difference between winning the pre-start, or the race.’ The great mystique and intrigue of the America’s Cup – or any
sport – lie in the imponderables, the areas that defy scientific analysis. While the teams have revealed four quite different responses to the rule they could all be right, or some could be wide of the mark.
CARLO BORLENGHI
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