The high-tech, high-powered America's Cup Class catamarans are capable of reaching speeds of up to 50 knots - or, to put that in more commonly understood metrics, around 90 km/h - but, as specialist sailing website Scuttlebutt points out, "the problem with making the boats faster and more specialised is that collisions can be terminal". With the teams racing up to two races a day in the intense month-long block of racing, the regatta could be an endurance test as much as it is all about speed.
"These boats are right on the edge and it could come down to who can actually keep it together," Team NZ boss Grant Dalton warns.
"You run this ragged edge between the need for reliability - because it doesn't matter how fast you are, if you don't finish you're not going to win - and being fast enough, so everybody is trying to judge it right down to the last second almost. It's easy now and again to step over the line, and that's what happened the other day [with the rudder breakage] - we stepped over the line."
Former Team New Zealand weather strategist and sailing guru Mark Orams says the speed wobbles, spin outs, nose-dives and capsizes we've seen to date generally stem back to one of two problems - operator error or a loss of hydraulic power.
All the control systems on board the 50ft catamarans from the wing to the daggerboards are powered by hydraulic cylinders in the boats, the grunt for which is provided by the grinders, or in Team NZ's case, cyclists.
The 50ft catamarans are hungry beasts, and quickly suck up energy as fast as the grinders can create it.
"You've only got a limited amount of hydraulic pressure to use, if you've used it all up, then you press a button and nothing happens - and that's the problem that boats have," says Orams.
"This is why the guys pedalling or grinding are so important - they're just feeding a hungry machine and keeping the hydraulic pressure as high as they possibly can. The helmsman and the guys controlling the trim on the wing and daggerboards need to be very precise and very conservation-minded about how much hydro they use. If they keep having to make little adjustments, they'll run out of juice."
BOW UP
When you see the boats bucking like wild broncos and the bows rearing up, that would suggest there is too much trim on the daggerboard. The main lifting foil (or daggerboard) is similar to a wing on an airplane. The foil is angled for take-off and once the boat is flying, it needs to be flattened out. Making these adjustments at speed is difficult, and if the crew get it wrong, the boat will keep pitching up until the foils get too close to the surface and break flow and come crashing back down on its hulls.
NOSE DIVE
A nose dive situation - when the bows of the catamaran dig deep into the water - occur when the foil has let go. There's two things that can cause this - ventilation or cavitation.
It's probably best Orams explains this one:
"What all these teams are trying to do is fly as high as they dare. The higher you can fly, the less drag you've got because you've got less structure in the water. But the higher you fly to the surface, the more likely it is you will drag air down the vertical [of the foil] and once you hit the horizontal and once it does, you lose grip and you're gone. That's called ventilation."
Cavitation is when the flow breaks free for some reason other than air coming from the surface, says Orams.
"That can be a piece of weed, a surface indentation or scratch, or that the boat has turned so quickly that the flow has been broken as the trim on the daggerboards has not been adjusted properly."
CAPSIZE
Capsizes are most likely to occur during manoeuvres. Tacks, gybes and mark roundings require finely choreographed crew-work, as the sailors work to set things up to deal with the turbulence, the loss of grip, the risk in a turn and keep the boats on its foils.
"That again all depends on the hydraulic fluid. If you've got good pressure then you can make multiple adjustments as you go through. Because of the turn rate of the helmsman, the amount of puff you've got, how the wingsail ends up moving from one side of the boat to the other - all of those things are variables that are really hard to predict so you're having to make little changes as you're going through the manoeuvre and that means you're using more hydraulic pressure to do this," says Orams.
"If you've got a really wide foil, then you've got much more stability and you don't have to do as much adjustment as you go through and you're more likely to stay on the foils. The problem with that is it's really slow in a straight line, because it's draggy.
"What Oracle have done, and why I think they are the ones that have capsized twice is that they are going for really thin and therefore really unstable foils, but they are really fast in a straight line. So they are pushing the envelope there, which means when they are coming to do turns, they're a lot less stable and they have to use more hydraulic fluid to adjust them, and if they lose hydraulic pressure, then it's inevitable that they're going to have a mistake and the thing will take over and tip."
