Our America’s Cup insider, Beppe Giannini, gives us a recap…
There is less than six months to when the new AC Class boats – known as AC50s – will be splashed, but the Cup organizers seem to have taken a perverse satisfaction in eliminating (yet another) mystique of the America’s Cup of yore: the bit-by-bit revealing of each team’s boat. Of course, we all know boats are now One Design, so it was no surprise Sail-World’s editor was invited to tour Oracle’s Core factory in New Zealand and take as many pictures as he liked of an AC50 being built – we don’t even know for which team. There’s one set of molds in NZ and an identical one in Europe that all teams are sharing. Core has built duplicate wing spars for four teams, which are already sailing aboard each team’s surrogate boats, the AC45 “Turbos”.
In fact, we already know what AC50s will look like, since the Ts, in addition to the same wing, are the same width, use the same crossbeams and daggerboards-wing-rudders geometry (rudders mounted on gantries like Moths).
Rudder gantry on ETNZ’s AC45 Turbo, to achieve the same geometry as on an AC50
Effectively, the only difference is the bows on the Ts are about 1m shorter, which on a foiling boat is irrelevant. Going one step further, cash-strapped teams such as Team France will take advantage of the fact that hulls are now built with upper and lower sections joined horizontally (rather than the customary symmetrical halves joined vertically). This has the effect that when the time comes to switch from their T to the AC50 they’ll simply cut off the hull’s lower sections and replace them with new ones, but keeping the same deck sections. Presto! This is also made possible by the fact that 3m long bow sections will be bolted-on, so that they can be replaced easily in the event of a collision, but mainly so that boats can be shipped in 40′ containers, obviously with a view to replacing AC45Fs currently used in the AC World Series for the next Cup. Incidentally, these bow sections are the last remaining parts to be laminated in each team’s Country of Origin, a (ludicrous) fig leaf for the stipulation of the original Cup Deed of Gift.
AC50 hull upper sections being built at Core, NZ. In the foreground the flange for the bolt-on bow is visible. Foto Sail-World
Getting back to the One Design concept, it’s well known that the only areas excluded are hydraulics, wing controls and daggerboards/rudders.
In terms of hydraulics, it has become apparent that available power from the crew will be a critical factor, to the point that the usual question comes up of whether foot-operated treadmills rather than grinding stations would be preferable on these non-heeling boats. There is no indication however of this being implemented, at least until now.
Wing flap camber and twist controls will be proprietary and fully hydraulic, putting an end to the pulleys-and-wires system borrowed from what C Class catamarans have been using for the past 40 years. The big challenge is to develop a self-tacking arrangement that also allows reverse camber at the wing tip.
But daggerboards are clearly going to be every design team’s make-or-break item. AC50s are limited to two pairs of daggerboards. Three additional sets may be trialed on Ts, plus a certain number of “uptips” may be swapped. Come race day, regardless, each team will have to make do with two sets, and the initial thinking was that there would be one “fresh wind” set with small uptips, and a “low wind”, large uptip and therefore draggier set that would let the boat foil sooner. This is similar to what Moths do, with two different foils being measured for a regatta.
What is being seen, however, is that due consideration is being given to the fact that large, high lift uptips will make it easier for a boat to stay on the foils when tacking, and there will be a lot of tacks during the races (more about that later). Also, such a daggerboard would be comparatively more heave-stable, requiring less frequent adjustments and thus saving scarce control power. At least, this is the reasoning behind the comparatively largish uptips being seen lately, notably a really humongous uptip seen sported by Oracle.
Really large uptip on one of Oracle’s Ts
On the same note, the marked bow-down trim sported in level flight by most Ts could be explained with the inherent drag of large uptips being offset by making them work in the “drag bucket” zone, i.e. running them at near-zero angle of attack and taking advantage of a laminar foil’s very low profile drag under that condition.
Bow-down trim on Team Japan’s T. Foto Knighton/Team Japan
Another notable aspect seen on the Oracle and BAR Ts is daggerboards that are canted outboard when fully extended, this is a logical arrangement in order to maximize righting moment, and possibly reduce the daggerboard backwash interference with the rudder. Remember Max Sirena complaining about that, and consequent rudder ventilation issues, on Luna Rossa’s AC72.
Outboard canted daggerboard, and unusual uptip, on BAR’s T
In terms of heave control, it seems clear that this is no longer obtained via surface-piercing uptips (daggerboard lift is reduced as the extremity of the uptip comes out of the water), as was the case with the first AC72s and is still done by simpler, smaller boats like the GC32. In fact, there’s a lot of associated drag (again, remember the huge “hole in the water” behind Luna Rossa’s daggerboard), plus this is unsuitable for upwind foiling, when hulls must ride close to the water surface.
Instead, designers are refining an uptip daggerboard’s intrinsic heave stability through the so-called leeway coupling, i.e. the interaction between leeway and lift. What happens is that a daggerboard’s vertical portion, while compensating the sail’s lateral thrust, generates a vortex, which interacts with the lift-producing uptip. If the hull rises too much the vertical portion is reduced and the vortex increases, disrupting the uptip’s lift. This effect is always present, but of course maximizing it so that it’s sufficient to make the boat’s foiling stable with a minimum of corrective input from the crew is not easy at all.
No doubt, this is the area to which each team is devoting most design effort, and unlike other components, daggerboards are fabricated in individual facilities under maximum secrecy. This applies to all teams except Team Japan, where daggerboards are being fabricated at Oracle’s Core plant; yet another indication (if one were needed) of Team Japan really being Oracle’s satellite.
Looking now at the actual activities on the water, the latest news is the launching of Team France’s T in Lorient. With the recent arrival of ETNZ’s boat, this completes the lineup of surrogate boats, and it’s telling that the two teams which had more problems in putting together a budget were last, and have no immediate plans to join the other teams training in the future race area in Bermuda.
BAR are doing the same, staying put in their huge base in Portsmouth, although probably more for image reasons since with two Ts sailing they do not appear to have budget issues. Or at least they didn’t until Brexit; local costs in Bermuda suddenly shot up by 14% for them.
Ts training in Bermuda
Teams having long transfered operations to Bermuda are of course Oracle, with their second and third T, Team Japan, which got the first Oracle T graciously handed over, and Artemis, also with two boats.
There was recently a sailing weekend as part of local festivities, and one Oracle, one Team Japan and two Artemis boats took part. Needless to say, Oracle won 6 out of 7 races with impeccable upwind foiling, and reportedly, almost flying tacks. Comments by local sailors were that the race area is exceedingly small at 1.4 nm long and 0.6 nm wide. In 9-12 knots of wind, it took just 25 minutes to complete three laps: a harbinger of the wham-bam-thank-you-ma’am, made-for-TV racing that’s in store for next year.
Bermuda race area
Article by Beppe Giannini