The final three. As Ineos battled with Prada, Team NZ were testing a more extreme interpretation (left) of their smaller, straight foils. No dihedral means less area which is a bonus at high speed but may imply less lift in the transition to full flight. By the start of the Prada Cup final the two protagonists had apparently adopted similar approaches of generous foil area with dihedral; however, there was now one major difference between the foil solutions of the two finalists – Prada had introduced a waisted bulb with aft-staggered foils (as used by Team NZ) while Ineos stayed with a more conventional intersection with just a small protruding bulb. The benefits of combining a waisted bulb with staggered foils were strongly advocated in Dave Hollom’s recent article, Neck on the Line (issue 492); among benefits of ‘aft loading’ the foil in this way is the evening-out of the different flow velocities past the foil-arm and foil (in a high drag area) also delaying the onset of cavitation – which may be another issue at the amazing speeds being achieved by these boats
much upright, and the cant angle of the foil is used to tune the balance between vertical and horizontal force rather than adjusting the heel angle. For whatever reasons the simple bow
wand was not adopted. What is a non- controversial assembly of carbon rod, Bowden cable and shockcord on the moth is not allowed on the AC75 where it would have to use sensors, micro-controllers and stored power. So the one-man control of the moth
must be divided between four or five sepa- rate crew members. And in fear of this turning into more of an E-sailing event through the use of autopilots, the class rule prohibits the crew getting any information about the ‘Yacht State’, as defined below. There are 19 references to the ‘Yacht
State’ in the class rule, each one designed to prevent the crew getting information about what the boat is doing. Getting information on the yacht state would make the crews’ lives much less fraught. The current rules seem like forcing Vendée Globe competitors to use only
paper charts, a sextant and a lead line. To tackle this complicated job-sharing
scheme, where five must become one, the teams have adopted quite different strate- gies. In an ideal world you would get Mr Spock to work out a mind meld process, but in the absence of that it becomes a more complex job. Ineos have set the boat up so that the
tactician is free to keep his head out of the boat. He isn’t part of the human battery. Neither is the helmsman, nor the two flight controllers and mainsail trimmer. This means quite a load on the grinding crew, but it doesn’t look as if the boat is ever starved of motive power. In the previous round-robins this focus on picking your way around the shifty courses set between Tamaki Drive and North Head paid divi- dends. Now in the steadier breeze of the eastern courses it doesn’t seem as useful. With this arrangement there is a port
and starboard flight controller and the helmsman, main trimmer and tactician swap sides at each tack and gybe. No matter how good the choreography the helmsman
35.108 Yacht state The specific condition of the yacht, comprising all of the following: (a) the position and orientation of the yacht in space (b) the position and orientation of any control surface (c) the position and orientation of a foil (d) the position and orientation of any force input device or part thereof (e) the stress, strain, tension and force in any part of the yacht, except in passive input devices (f) other force-related quantities in any part of the yacht (g) the volume, velocity, flow rate or pressure of fluid within, or acting on, any part of the yacht (h) all absolute measures of the above and quantities measured relative to each other (i) the water or wave height or velocity relative to the yacht (j) all time derivatives of the above (k) all quantities derived from any of the above, and (l) all quantities from which the above can be derived or approximated.
50 SEAHORSE
must scuttle around the leech of the main every time, while the tactician steers the boat, and then the tactician and trimmer swap over. There is a lot going on at each change of tack as the onboard audio shows: ‘my wheel’ (steering?), ‘my rudder’ (rudder lift?), ‘my roll’ (?), ‘my pitch’ (rudder lift?). All of this goes on right when the boat needs to accelerate back up to speed. Onboard Luna Rossa there is a port and
starboard helmsman who stay put, and now only the mainsheet trimmer/strategist swaps sides. Initially having two helmsmen seemed to disrupt more than having one man in charge, but with practice and a few good results the system is bedding in, and Luna Rossa are a model of consistent ride height and smooth manoeuvres. Also the hand-over comms on the Italian
boat are much reduced, ‘my wheel, my trav’, which suggests that the active helms- man has control of the mainsail traveller. It all looks pretty smooth, and until Ineos exert some pressure by winning the first cross it could stay that way. Pre-starts have been a bit of a letdown,
it’s a high-speed slow bicycle race (coming off the foils at 18kt being the equivalent of putting your foot down). There is a mini- mum of interaction and the starts are timed runs from the moment of entry, aided by super software and time spent double- foiling so you don’t reach the boundary too quickly and get forced into making more manoeuvres than you need to. As I finish writing this my father
phoned up from the retirement village. He and his pals had watched the racing and enjoyed it at the level of a travelogue, but they were wondering how it was possible to lose a race by 800m. Good question, Dad, keep them coming.
q
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