Farewell Spinnaker. Do AC 75s only go upwind? All “fault” of the apparent wind PHOTO

“Qhese boats always go upwind. There are no more sail changes now. Crews no longer maneuver. We miss the spinnakers.” So many times we have heard this refrain about the new America’s Cup. A “controversy” that had already begun with the AC 50s in the Bermuda edition and continued with the “disappointment,” from a part of the public, of the non-return to more traditional monohulls. While these criticisms are in part clichés to be debunked, it is true that the AC 50 first and the AC 75 later brought to the big Cup stage a new way of sailing that made the more “traditionalist” public lose their bearings. The secret of this novelty has a specific name: apparent wind.

A MATTER OF APPARENT WIND

Let’s start with its definition: what is apparent wind? It is the vector sum of the true wind plus the forward wind, and ultimately it is always on the apparent that any sail propulsion boat adjusts its “wings.” Basically what the nostre sails feel is always and still the apparent wind. This is because, at whatever speed our boat is sailing, there is a forward wind coming from exactly the opposite direction of our progress. The forward wind causes the direction of the apparent to always be at a lower angle than the actual. Let’s take an example: if we sail on a real of 80-90 degrees at 5 knots, the apparent will be about 60-70 degrees, and it is on the latter figure that we will adjust our sails. While this occurs on slow boats sailing at a few knots of speed, in the case of AC 75s or foil boats in general the phenomenon is somewhat “exaggerated.”

ALL THE FAULT OF THE FOILS

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The lowering of hydrodynamic drag that is achieved by foils results in a speed that at slack can even triple the intensity of the wind. We know that the apparent wind always has a narrower angle than the true wind because it is influenced by the speed of the boat and thus the forward wind. With such an exponential increase in speed relative to the wind, the result is that the forward vector increases in tandem and the apparent is almost always close to upwind, even when sailing on slack.

When a boat like an AC 75 rests at the windward mark, the higher the speed, the more the trimmers caulk the sails. If, for example, the boat, due to an error by the helmsman or foil trim, touches the water, the speed collapses and the apparent wind shifts violently aft. We will see the immediate reaction of the trimmers as they let go of the sheets to adapt to the new situation, and they will return to caulking as soon as the boat resumes flight and the apparent returns toward the bow bow.

It is basically an almost counter-intuitive type of adjustment compared to what we would do on a traditional boat.

Under these conditions it seems obvious that the use of typical sails from load-bearing gaits is impossible, for the simple fact that as soon as the boat gets on the foils they would immediately deflate due to the shift of the apparent toward the bow. The only sails other than jibs that we will see on the AC 75’s bow will be similar Code 0s with a fairly skinny leading edge, which will most likely be used only when the wind drops below ten knots. Above this intensity the Tails will be useless if not counterproductive.

ARE THERE NO MORE ADJUSTMENTS?

Nothing could be more false. From the few images seen of the AC 75s, we can already see a lot in terms of adjustments. One seesw, for example, the base of the mainsail being very fat as the boat takes off, or the sails twisting very hard depending on the conditions of the swell and wind strength. Flying the foils of a boat like an AC 75 is something complex that requires constant adjustments and changes in trim, sails and appendages to make the boat stay foiling.

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It is true that we no longer see “glaring” adjustments such as the mainsailer “firing” the sheet at a turn when going from upwind to downwind, but that does not mean that AC 75 crews are not constantly working on the sails. Indeed, the adjustments have probably multiplied since one is no longer sailing in a two-dimensional situation but has moved to a three-dimensional sail. There is no longer only hemming and hawing, but also high and low referring to flight.

WON’T WE SEE

THE STERN MARKINGS?

On how race tactics change we will devote an ad hoc in-depth study. For now, the question we are interested in asking is: will we still see classic match race duels in the stern? Of course they do. The fact that AC 75s always sail with the apparent almost upwind does not mean that the classic “attack from behind” is no longer applicable. However, coverage on the true wind remains effective and is a valuable disturbance to the boat ahead, so classic match race dynamics can be expected with coverage attempts and stern swings will certainly be fertile for attempting overtakes, not least because full foiling gybes will not be easy to execute and the crews’ ability to maneuver will be crucial.

And in match racing, what tactic is more classic than making the opponent ahead of you maneuver to induce them into error?

A PROBLEM OF UNDERSTANDING

Like all new things, these take some time to be understood, to become familiar and to be understood even by a generalist audience.

In this sense, it must be said, the communication effort of the teams seems a bit “lazy”: more concerned about not giving sensitive information to opponents than explaining the workings of these boats to fans.

After all, the history of the America’s Cup is not that of a regatta whose purpose is to divulge something to the public, but to show on the water the spectacle of uncommon boats, often at the absolute cutting edge of technology.

The Cup was never concerned about its innovations being transferred to everyone’s sail, because the Old Pitcher, after all, was never for everyone. It is a kind of Holy Grail of sailing, in which very rich paperons compete by hiring the world’s best sailors on the most high-tech boats in existence. So it has always been and so it will continue to be. It only matters who wins, and there has been no second for over 150 years.

Mauro Giuffrè

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