WHY ARE ETNZ TESTING THEIR NEW M2-1 MAINSAIL IN LIGHT CONDITIONS?

THE BASE CASE ARGUMENT
Establishing the crossover between the M1 and M2-1 is perhaps a very plausible objective. But testing the M2-1 in such underpowered conditions suggests Emirates Team New Zealand may be particularly interested in the lower boundary of the sail's operating range. For Taihoro, the critical question is whether the new M2-1 can generate sufficient power to take off, accelerate and remain foil-borne in conditions where the larger M1 would traditionally be expected to have an advantage.

This is a fundamentally different exercise from testing the M2-1 in 15–18 knots, where excess power and drag reduction become more important. At 6–8 knots, as the Recon team recorded in the first part of the session today, ETNZ is likely examining three distinct performance regimes: Firstly, the displacement-to-foiling transition: Can the M2-1 generate enough aerodynamic force to achieve take-off? Secondly, in marginal foiling conditions, once airborne, can it maintain stable flight through lulls, manoeuvres and changes of heading? (we saw lots of manoeuvres today). Thirdly steady-state foiling where once established on the foils, does the M2-1 produce better VMG than the M1 despite its smaller area?

This last question is where the VPP (Velocity Prediction Programme) and its polars (the boat's predicted speed across different true wind speeds and angles) become particularly interesting.

IS THE CROSSOVER MUCH LOWER THAN EXPECTED?
If the new M2-1 can achieve the same steady-state VMG as the M1 in 7–8 knots, that would be an important result as it would suggest that the smaller mainsail's potential aerodynamic efficiency advantage is sufficient to compensate for its reduced area, even when the boat is relatively underpowered. That could give ETNZ a much wider usable wind range for the M2-1.

However, there is a critical complication in that a sail can produce better VMG once airborne while being worse at getting the AC75 onto its foils. That means ETNZ may need two separate crossover assessments - one for take-off and another for sustained foiling performance.

VPP MAY BE MOST INACCURATE AT THE BOTTOM OF THE RANGE
In steady flight, the VPP can predict a balance between aerodynamic driving force, hydrodynamic resistance and the loads supported by the foils. But at 6–8 knots, small changes in sail force can produce disproportionately large differences in performance.

A yacht might accelerate successfully to take-off speed with the M1 but struggle with the M2-1. Take off might be fine with either mainsail, but the sailors may find that 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 they may produce superior upwind VMG with the M2-1 but lose that advantage after tacks.

These are not minor differences. They can determine whether a sail is viable in a light-air race. The design team will therefore be interested in comparing predicted polar performance against the probability of actually achieving and sustaining those speeds. A conventional steady-state polar does not fully capture take-off time, touchdowns and manoeuvre losses. ETNZ would need additional transient-performance analysis or empirical corrections to account for those factors.

IS THE NEW M2-1 MORE EFFICIENT AT GENERATING DRIVE?
One theory could be that ETNZ has improved the M2-1's aerodynamic efficiency enough to challenge the M1 in marginal conditions so today the designers and sail team could have been looking at all manner of inputs such as the lift-to-drag ratio, camber distribution, jib interaction, aeroelastic behaviour or sheer acceleration

At 6–8 knots, the objective may have been to establish the minimum viable aerodynamic force required to take off and then determine whether the M2-1 can deliver it more efficiently than predicted.

WAS IT BEING TESTED DELIBERATELY OUTSIDE ITS EXPECTED OPERATING RANGE?
Another strong possibility as design teams do not 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, the designers can use a marginal-wind session to investigate whether the predicted performance deficit is real or whether alternative trim settings can recover some of that deficit. They might also be looking at whether the model accurately predicts the yacht's take-off threshold or are performance differences attributable to the mainsail or to the foil and flight-control settings. A failed test could be extremely valuable if it identifies why the theoretical model differs from reality.

MANOEUVRING PERFORMANCE MORE IMPORTANT THAN POLARS?
Today we saw the sailors executing a lot of snaking ‘S’ manoeuvres and turns similar to how they sailed on the 8th October where Seb Menzies specifically highlighted the importance of high turn rates and low-speed manoeuvrability.  The 12^th October Recon report then recorded sailing in approximately 4.5–8 knots, with the M2 mainsail, J2-1 and later J3-1 jibs. The report suggested that the team took almost 2 minutes to take off before they practised tacks, gybes, 360-degree turns, pre-start manoeuvres and longer speed runs.

Both days, and today, suggest an important second objective alongside polar validation in 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.

Magnus Wheatley