Join Matt Brown, around the world sailor Bianca Cook and AUT Sailing Professor Mark Orams to preview all of the action ahead of the Prada Cup. Video / NZ Herald
OPINION:
Things can turn bad very quickly in the AC75 yachts which were introduced for this America's Cup.
Team New Zealand's capsize during practice racing was a brutal reminder of how tricky these foiling machines are to sail.
The slightest mistake can see things cascade and leave the boat onits side in seconds and the team looking pretty ordinary. Thankfully there was no damage to people or equipment.
It was the first time one of the new versions of the AC75 has capsized. With hundreds of hours on the water under the belt, you might think it should not happen. But that would ignore how close to the edge these yachts are being pushed. Foiling yachts are so precariously balanced that small variables can have dramatic effects.
The video reveals a number of factors which led to Monday's dramatic events.
First, there were highly unstable conditions in terms of wind strength and direction. This is hardly new to any top sailor but it was a contributing factor which laid the foundation for what occurred.
Secondly, Te Rehutai has an inherently less stable foil design than the rival AC75s. The long and slender foil wings with a flat angle (noticeably different to the anhedral or upside-down "Y" shape of the others) are a low drag design. While potentially faster, this design means the flight control - and particularly the angle of attack adjustment - is much more critical.
Very small changes can result in the yacht crashing down into the water, or conversely leaping up into the air then crashing down. Small events cascaded into one large one.
Team New Zealand starting to tip during the capsize in practice. Photo / Photosport
TNZ were sailing downwind and the capsize occurred after a gybe (changing direction so the wind comes from one side of the yacht to the other).
A gybe is a complex manoeuvre which relies on a stable approach and the ability to keep the apparent wind forward.
The video of the capsize shows it was set up by a poor approach into the gybe when TNZ splashed down and dramatically lost speed as skipper Peter Burling started to turn the boat.
It is counter-intuitive, but speed is your friend when gybing. The ability to keep the yacht fast and stable means that the apparent wind stays forward and the pressure/force on sails, foils and the entire yacht are lower. The splash-down before the turn into the gybe meant that Te Rehutai was loaded and less stable going into the turn.
As Burling steered the yacht out of the turn and the wind direction changed to the opposite side of the yacht Te Rehutai was concurrently hit by a strong gust of wind. Burling reacted to this quickly and correctly by turning the yacht away from the gust. However, the acceleration this caused generated more lift on the foil and the boat raised up quickly.
The effect of this was a need to bring the flight height back down, which flight controller Blair Tuke was onto quickly. However, this fast adjustment to bring the nose down consequently raised the back of the yacht up and at this point Burling "lost the rudder" meaning he lost any steerage and therefore control of the yacht. Game over and in they went. This all occurred in five seconds.
Team NZ capsize Te Rehutai during an America's Cup practice session. Photo / Photosport
All the teams will watch and learn from the video, but a possible repeat can't be entirely ruled out with these boats. The World Series regatta before Christmas emphasised that racing these yachts is not easy.
But Team New Zealand might send race officer Iain Murray a few boxes of their beverage sponsor product as thanks for adding in the two extra days of practice racing.
Mistakes happen most under racing pressure, which is also when you learn the most.
They got away with it without major damage and with good video footage to learn from. It was a blessing in disguise.
