Emirates Team New Zealand's Recon footage from today threw up an interesting puzzle. The crew took their new M2-1 mainsail out in winds of just 6 to 8 knots, conditions that look, on the face of it, far too light for a sail built for heavier airs.
So what's going on?
The simplest explanation is that ETNZ is hunting for the crossover point between the M1 and the M2-1, the wind strength at which one sail becomes faster than the other. But testing the M2-1 at the bottom end of the wind range, rather than in the 15 to 18 knots where excess power and drag reduction matter more, suggests something more specific. Taihoro's designers may want to know whether the smaller sail can generate enough power to take off, accelerate and stay foil-borne in conditions where the bigger M1 would normally hold the advantage.
That's a different question entirely from testing drag reduction in a solid breeze.
At 6 to 8 knots, three things seem worth examining. Can the M2-1 generate enough aerodynamic force to achieve take-off at all? Once airborne, can it maintain stable flight through lulls, manoeuvres and changes of heading, and there were plenty of manoeuvres on the water today. And in steady-state foiling, does the smaller sail actually deliver better VMG than the M1 despite having less area to work with?
That last question is where the VPP, the team's Velocity Prediction Programme, and its polars become genuinely interesting.
If the M2-1 can match the M1's steady-state VMG in 7 to 8 knots, that's a significant finding. It would mean the smaller sail's aerodynamic efficiency is enough to offset its reduced area, even with the boat relatively underpowered, and that would hand ETNZ a wider usable wind range for the newer sail.
There's a complication, though. A sail can produce better VMG once airborne while being worse at getting the AC75 onto its foils in the first place. So ETNZ may need two separate crossover assessments, one for take-off and another for sustained foiling performance, rather than a single tidy number.
The VPP itself may be least accurate exactly where it matters most here.
In steady flight, the programme can predict a balance between aerodynamic driving force, hydrodynamic resistance and the loads supported by the foils reasonably well. But down at 6 to 8 knots, small changes in sail force can produce disproportionately large differences in performance. A boat might accelerate successfully to take-off speed with the M1 but struggle with the M2-1. Take-off might be fine with either sail, but the sailors may find they can maintain flight more consistently with one. The team might achieve a higher peak speed with the M2-1 but suffer more frequent touchdowns, or produce superior upwind VMG with the M2-1 and then lose that advantage after tacks.
None of that is trivial. These differences can determine whether a sail is viable in a light-air race.
A conventional steady-state polar doesn't fully capture take-off time, touchdowns and manoeuvre losses, so ETNZ would likely need additional transient-performance analysis or empirical corrections to get a true picture.
There's also a design angle worth considering. One theory is that ETNZ has improved the M2-1's aerodynamic efficiency enough to challenge the M1 in marginal conditions, and today's session may have involved the designers and sail team looking at inputs such as lift-to-drag ratio, camber distribution, jib interaction, aeroelastic behaviour or sheer acceleration. The objective may have been to establish the minimum viable aerodynamic force required to take off, then determine whether the M2-1 can deliver it more efficiently than predicted.
Equally, design teams don't always test a sail in conditions where they expect it to be fastest. Sometimes the purpose is to expose weaknesses in the model.
If the VPP predicts the M2-1 should be significantly slower than the M1 at 6 knots, a marginal-wind session is a good way to check whether that predicted deficit is real or whether alternative trim settings can recover some of it. It can also help establish whether the model accurately predicts the yacht's take-off threshold, and whether performance differences are down to the mainsail or to the foil and flight-control settings. A failed test can still be extremely valuable if it identifies why the theoretical model differs from reality.
Manoeuvring performance might matter just as much as the polars.
Today's session included plenty of snaking S-manoeuvres and turns, similar to how the team sailed on 8 October, when Seb Menzies specifically highlighted the importance of high turn rates and low-speed manoeuvrability. The Recon report from 12 October recorded sailing in approximately 4.5 to 8 knots with the M2 mainsail, J2-1 and later J3-1 jibs, with the team taking almost two minutes to take off before practising tacks, gybes, 360-degree turns, pre-start manoeuvres and longer speed runs.
Taken together, the sessions point to a second objective running alongside polar validation: understanding how the M2 sail plan performs when the yacht is forced away from its optimum steady-state sailing mode. An M2-1 might have excellent straight-line polar predictions but lose more speed in an aggressive pre-start turn than the M1. Equally, a more efficient sail could help Taihoro accelerate out of a manoeuvre, even if its absolute maximum driving force is lower.
For match racing in Naples in 2027, that could be decisive.
