How AI will make boats go faster (in defiance of cavitation)
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How a Swiss team is using artificial intelligence to combine ventilation and cavitation and break the sailing speed record
Cavitation, a solvable problem?
During the America’s Cup, we have spoken several times about the physical limitations that the designers of today’s AC75s are up against. Indeed, the problems of ventilation and cavitation raise the level of difficulty facing engineers, with cavitation in particular placing an almost insurmountable dam on the maximum speeds that can be reached by foil boats, even large ones such as precisely the AC75s used in the Cup.
60 knots: a sound barrier for water
The challenge is reminiscent of that of the pioneering days of aeronautics, when the barrier of Mach 1, that is, the speed of sound in the air, was a difficult wall for engineers to overcome, although theoretically within reach given the introduction of jets. However, the closer one got to that limit, the more complications increased exponentially.
Sailing is somewhat experiencing a similar situation with the advent of the foil era, which allows theoretical speeds in excess of 50 knots, but with most of the profiles currently being used that, as they approach 60 knots of speed, go on to ingenerate the phenomenon of cavitation to a level that brings both conducting and structural risks. A phenomenon so dangerous, if unchecked, that in Cup regattas with sustained winds, we have often seen crews choose shallower and slower aft courses, even at the cost of losing VMG, in order not to sail above 50 knots, even though the impression was that the boats had a chance to go faster. If until a few years ago, therefore, this barrier appeared practically unattainable anyway, and therefore not worthy of in-depth research, with the last Cup and with the increasingly rapid evolution of the foil world, it has begun to represent a concrete limit to performance, so much so that, for example, in Barcelona there was speculation of moving to even smaller boats (such as a possible AC65) in order to at least partially move away from this physical limit and expand the margin of development on profiles.
SP80: the Swiss aiming for a record by combining artificial intelligence, ventilation and cavitation
Against this backdrop emerges the work of the SP80 research team, a team of 40 engineers from the Lausanne Institute of Technology EPFL (Ecole Polytechnique Federale de Lausanne) who are working on a prototype foil “boat” that can reach 80 knots of speed.
Quotation marks are in order since the “boat” is a prototype that looks more like a spaceship than a boat: a kind of small trimaran, towed by a kite, but capable of flying on foils just above the surface. SP80 actually stands for Speed Potential = 80, and the idea is to be able to find foil geometries such that cavitation no longer becomes an insurmountable or dangerous limitation. The basic principle is simple in theory, but ingenious and technologically advanced in practice: the engineers in Lausanne have in fact discovered that the phenomenon of cavitation, by its nature unstable and difficult to manage, can instead become controllable if it is associated with it, in an obviously carefully calibrated manner, that of ventilation. Indeed, simulations and tank tests carried out by SP80 engineers have shown that the vapor bell that is created on the upper surface of the foils above 55-60 knots of speed takes on stable shapes and characteristics, therefore controllable and above all predictable, if air is injected into it. This process then actively exploits the phenomenon of ventilation to make the cavitation of the profile governable.
Artificial intelligence to find the right profile
A technical innovation of this magnitude is, of course, moving into largely uncharted territory, especially with regard to the shapes of the foils themselves. And this is where, at the dawn of the AI revolution, artificial intelligence comes in: engineers at SP80 have harnessed AI with advanced algorithms to generate an enormous amount of simulations, testing the performance of a wide range of profiles.
The result? A completely new design: a radically different, wedge-shaped profile that has proven to be the most effective in generating lift and creating a stable air and vapor cushion on top of the foil. This discovery could (theoretically) open wide the door to a new era of foils, in which cavitation is no longer an insurmountable barrier beyond 60 knots.
In 2025 the speed record attempt. High-speed transportation is the goal. The Cup? There is still a limitation
According to the statement, the SP80 team will attempt for the first time just in 2025 to break the current sailing speed record, set by Paul Larsen in 2012 with his Vestas Sail Rocket at 65.45 knots and still unbeaten after more than a decade. If SP80 succeeds in the feat, we will have the first demonstration of the feasibility of foils that we might call “controlled cavitation,” with a likely quick repercussion on the world of boating and shipping. Clearly, SP80’s work is not aimed specifically at the America’s Cup, but is designed to attempt to revolutionize high-speed shipping.
It is clear, however, that it would also be revolutionary for the world’s oldest sporting trophy, since AC75s are among the fastest foil boats and suffer most, as mentioned earlier, from these kinds of limitations. There is, however, as far as the America’s Cup is concerned, another important limitation to be taken into account, namely the need for boat foils to perform optimally over a wide range of wind conditions, thus not being able to optimize the profiles only for maximum speeds at high cavitation. This does not detract from the fact that designers’ imaginations could run wild, even with smaller and smaller foil sizes deliberately cavitating in all conditions. The whole course will therefore be interesting to follow, to see if this important new frontier in the foil world will open up this year.
Federico Albano
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