The state-of-the-art monohulls racing off Auckland this week are as far removed from the schooners which first competed for the silver trophy in the midth century as a modern Formula One car is from a Model T Ford. The 75 foot Challenger yacht Luna Rossa had maxed out at Despite that raw speed, TNZ helmsman Burling said, the handling was similar to the much lighter 49er two-handed dinghy in which he won Olympic gold for New Zealand with Blair Tuke in Read More.
I think the incredible thing about these AC75s is they're a massive boat but just how dynamic they are to sail. To put that into perspective, the entire boat itself with all equipment but without the crew weighs between kg and kg. It is partly due to this that you will see some teams with bulbs on their foils. If you decide to go for a skinny foil wing which would be low drag and so faster then there will not be enough volume to cram sufficient material in to make the foil weigh enough.
So some teams have decided to add a bulb in order to make it weigh enough but to also keep a less draggy, slimmer foil shape. As with everything on the AC75, the mainsail is a relatively new concept. It consists of two mainsails which are attached to both corners of a D-shaped mast tube. This has the effect of creating a profile similar to a wing. But there are drawbacks with a wing: they cannot be lowered if something goes wrong and require a significant amount of manpower and a crane to put it on or take it off a boat.
One reason a wing makes for such a powerful sail is that the shape can be manipulated from top to bottom fairly easily with the right controls. With the AC75 the designers wanted a sail that could have some of this manipulation, produce similar power but could also be dropped while out on the water. In addition to the usual sail controls, within the rules, the teams are allowed to develop systems for controlling the top 2m of the mainsail and the bottom 1.
What this means is that the teams are able to manipulate their mainsail in a number of different ways to develop power and control where that power is produced in the sail.
But it also means that they have the ability to invert the head of the sail. The advantage here is that instead of trying to tip the boat to leeward, the very top of the sail will be trying to push the boat upright and so creating even more righting moment.
The disadvantage is that it would come at the cost of increased aerodynamic drag. Each team has incredibly powerful Computational Fluid Dynamics CFD software packages and simulators in order to try to understand the various gains and losses.
To make these simulators and computer projections as accurate as possible each team has been getting as much data as they can over their three year development cycle. They even have some Mercedes staff out with the team in Auckland assessing their data. These are just the most obvious differences, and there will be many more variations beneath the surface, especially in the complex control systems. Yet despite dissimilarities, the speed differential between teams in the Prada Cup varied only by fractions of a knot, putting the emphasis on dominating pre-start manoeuvres, reading the wind shifts and match racing the opponent.
These will all play a part in the Cup match too. At the wheel, the Italians have a set-up never seen before, with straight-talking Australian Jimmy Spithill helming on starboard and Italian Olympic sailor Francesco Bruni helming on port.
When one is steering, the other acts as flight controller and trims the foils. It is a formidable partnership. Bruni, meanwhile, has three Olympics behind him and several Cup campaigns himself. While this unconventional division of control between the two helmsmen prompted observers to shake their heads at first, it has proved highly successful. Spithill has suggested that the arrangement allowed them both to accelerate their skills, while at a very practical level it means no one has to jump out of the cockpit and cross the boat during high-speed G-force tacks and gybes before settling back into continuity in a new position.
Indeed, it has been so successful that Emirates Team New Zealand have been experimenting with changing to the one-helmsman-per-side arrangement, split between Peter Burling and Glenn Ashby. Watch out, this may come into play at some point. Meanwhile, they have increasingly brought into play the tactical skills of Pietro Sibello, an Olympic 49er sailor, who is to be seen popping up to read the wind and the race course and feed back into the strategy. The pre-starts. Each team must enter the start box from opposite ends at the two minute mark.
They jostle for the best position with the aim of hitting the line powered up exactly as the clock counts down to — and in front of their opponent. To get an advantage, each team will look to dodge, weave, box out their opponent, put a penalty put on them, or execute some other perfectly legitimate but edge-of-the-seat manoeuvre. These minutes can be among the most exciting of a whole race, and may set the tactics and playbook for all that follows so are not to be missed.
Mark roundings. Teams can round either one of two marks at the top or bottom of the course, so watch for splits here, close overlaps and other tactical manoeuvres. As the boats bear away at the upwind mark rounding they head into a power zone, speeding up rapidly. This is where we have seen the AC75s exceed 50 knots of speed and get unstable and into trouble with flight control. Light winds.
The AC75s have sometimes struggled to foil in winds of under 8 knots. When they come off their foils they suddenly go from supersonic to super-slow. Comparatively huge distances can open up or disappear in a flash if one team finds a puff and gets flying while the other is floundering. On light days, everything can turn inside out in seconds. Strong winds. The same is true in big winds.
Mistakes in crewing and sailhandling can be punishing when these massively loaded boats are fully powered up. When the winds are up, the pre-starts and mark roundings are likely war zones.
Match race tactics. Some thought the equivalent of hand-to-hand combat could never happen in the AC75s, but they have turned out to be agile and the crews surprisingly willing to throw them into some very close quarter spots. They are also able to mark opponents tack for tack and gybe for gybe round the course to defend a lead and deny their opponent a passing lane. Watch for these clever displays of aggression and stealth.
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