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It should be noted that from this edition the jibs will be self tacking with rail, unlike the past where adjustment was done in a more traditional manner with the two sheets, adjustable points, and winches.
This seeming detail has actually brought with it a wide range of issues, especially for adjustment in the stern.
It is indeed necessary for crews to maintain control of the leech and more generally of the shape of the jib even when leaving the sheet to the carriers, and for this various solutions were seen.
The trolleys of the self-tacking jibs are all in a trench, often sealed by a kind of zipper from which only the sheet comes out, but from what little we have seen the shapes of the staysail are not the same among the various teams.
The adjustment of the mainsail, with the uniqueness of the double skin from which it is formed and with the rotating mast, remains one of the points most shrouded in secrecy by the teams and at the same time with great re- search and greater differences (as far as what very little we could see).
New Zealand seems to have a simple but effective control system, while the complexity of the system seems to be higher for Luna Rossa and Alinghi.
Coming then to the sail plan, it is one of the major points of research by the teams.
Already since the last Cup, it had been noticed that the surface and shape of the upper part of the jib had an important influence on the overall perfor- mance, and in theseweeks of training we have seen several experiments in this regard on the water, but until the re-gates it will be difficult to have definitive answers.
AC 75 America’s Cup – I FOIL
The foils of Team New Zealand and Luna Rossa compared.
The most distant boat in the photo was Luna Rossa, but despite the perspective LR’s foil appears larger, in width.
Differences on shape as well, with the Italian one straight and the Kiwis’ curved instead.
The curvature, if deformable, could delineate an appendage that changes shape depending on the speed of the boat and the load it is subjected to. Similarly, there is still no certainty about the most important elements for performance, namely the foils.
For the time being, all teams have shown fairly similar foil sets, with a central bulb, abackward-shifted surface, not V-shaped, but still with a slight downward curvature but with the tips pointing upward to cut the water surface.Differences for now have been seen with more or less extreme aspect ratios and more or less generous flap sizes (Alinghi has shown larger flaps for example than New Zealand), but even on this point experimentation is the order of the day, with boats spesso they go out to practice with different foils between starboard and port to make comparative tests, and only with the start of the regattas will we have the first answers about this.
What is certain is that the boats have shown that they can take off already with wind intensity around 6 knots, so already showing a significant step forward compared to the previous edition of the Cup.
So many similarities and differences between these very special boats, but only the race course will tell us who had the right insights.
AC 75 America’s Cup – THE HULL
The hull, the clearly most visible element, tells so much about the design philosophy, although it is no longer features such as stability of form or bow volumes for passage over the wave to be the focus, but rather all the features necessary to fulfill the new tasks the princely element must fulfill On an AC75.
The first purpose is structural, and there is an exhaustive quest by all the squa- ders to lighten the structures as much as possible and to concentrate the center of gravity down and, longitudi- nally, at the height of the foils, to improve stability in flight.
The T-shaped main section has been the classic choice for all, but variations on the theme are many, with aerodynamics as the guiding line: with speeds approaching 50 knots, the dynamics of flows above deck and below hull is critical to performance, and the hull and deck shapes are (almost) entirely designed with this one end in mind.
The distribution of hull volumes is very different then among the various teams, especially vertically.
They range from extremes such as Luna Rossa and Team New Zealand with a pronounced, deep V-shaped hull shape, to the e- extreme opposite of Ineos, with asquared-off keel line (one of thehallmarks of these boats), and more concentrated volume at the top. Luna Rossa’s solution has the hypothetical downside of a slightly larger exposed surface area (and thus resistance), but, at the same time, it should provide better penetration, and be a boastingague in managing the flight attitude at the water surface.
Indeed, we know that the ideal flight attitude for an AC75, the one that pro duce more stability and performance, it is actually as low as possible on the water, slightly apprua- tive, and the thin lines of Luna Rossa and Team New Zealand could prove useful in staying above the water with some ela- sticity, especially in non-flat waves.
Remaining on the bows are the two characteristic “bulges” on Alinghi’s hull in the upper forward part of the hull, aimed at directing and accelerating the air over the lower part of the jib and, consequently, starting to channel the aerodynamic flows already from the bow, so as to try to steer, in cascade, what happens then in the aft part.
Alinghi’s bow shapes, with the bulges in the deck at the height of the jib attachment, deserve a closer look.
They probably serve to better channel airflow into the lower part of the jib and toward the mainsail.
The aft exits are similar for all, thin and tapered, in which the keel itself plays a fairly important role in containing the rudder steering components.
The space, in fact, at the stern is very small, given how much to approach hull and deck, and all teams try to keep the deck as clear as possible given the crucial importance, as we will see in a moment, of just the upper aerodynamics.
For this reason, almost all have tried to increase the volume of the “keel” in the aft area, in order to maximize the space available for housing the steering systems and to be able to minimize the volume occupied by the box in the deck.
An exception to this rule is Team New Zealand, with a very thin keel, aimed at optimizing output effects, as opposed to the others, which instead have a more or less extensive surface area perpendicular to the direction of flow.
Interesting then, in this sense, is the actual skeg adopted by Ineos in front of the rudder, a kind of upside-down fin, which should have the dual function of improving the aerodynamics of the stern and of closing laterally the gap created in conditions of navi- gation with the boat bowed.
AC 75 America’s Cup – THE COVER
Ascending then “above” the boats, we come to the element that perhaps most of all represents the exploratory work of the teams and which at the same time plays an even more important role than the hull, namely the deck plan.
The first, and simplest, feature we notice for all boats is the deck profile that is not flat, but clearly aimed at generating some lift.
This on the one hand helps the boat stay airborne, devolving some of the lift to aerodynamics as well, and on the other hand has a beneficial effect on the sail plan.
The acceleration of the flows around the curvature of the deck goes to increase the apparent in the lower third of the sail plan with obvious benefits.
That is why everything exposed on deck becomes a source of aerodynamic disturbance that goes to affect performance, first and foremost the crew, with the cockpits containing them now something extreme.
Just look at Luna Rossa’s front cowl, which provides visibility without having to expose the head, or the fact that everyone has placed the position of the riders in the most aft available part of the cockpit. Minimizing aerodynamic drag and lowering the weight center of gravity is an important goal on the AC75s.
American Magic has implemented the most “extreme” solution, with grinder riders working in an inner, unexposed zone and pedaling in a virtually prone, almost unnatural position. From what has been seen and learned, for those who go down to the sea to ride is obliged torior in racing to perform their task without ever raising their heads.
And it is in this regard that the solution adopted by American Magic is of particular interest, the only ones to have the riders on the innermost part of the boat, even lower as a position, pedaling in a position bordering on unnatural, but with the purpose of lowering the center of gravity and concentrating mass around the foil arms.
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