America's Cup: Behind the scenes of Team New Zealand's hi-tech win in Bermuda
How did Team New Zealand do it?
Reclaiming the America's Cup is no small feat and the team's hi-tech pedal-powered boat combined with the speed and physical strength of the crew go a long way to explaining the win.
Let's take a look at the boat, which is basically a catamaran with an aircraft wing for a sail balancing on top of two big canoes on top of two or four surfboards.
The crew need to balance the boat as it flies through the air, while the wind provides lift, in turn controlled by the rudder and foils skimming through the water.
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To win, Team New Zealand were faster, stronger, and more manoeuvrable.
They were the first team to achieve 100 per cent 'fly time'. But remember, the only thing powering the boat is wind.
All the adjustments by the crew harness that wind.
Typical 'takeoff' speeds are around 15 knots and sailing speeds are about 30kts, although top speeds have hit 50kts (90kmh).
Hydrofoiling - also known as foiling - and 24-metre high 'wingsails' are the main technology to know about - the former is the underwater apparatus that lifts the hull above the waterline and the wing is the rigid sail, more akin to an aircraft wing.
Teams have been experimenting with the shape of the foils and have settled on designs they say maintain stability.
When you turn a boat, lift is lost, so the set-up needs to be adjusted quickly to maintain speed, and therefore lift, otherwise crews risk nosediving, or pitch-poling.
Rules say crews must all produce boats of similar dimensions and design, while leaving room for experimenting with the daggerboards and the hydraulic system for moving the foils and the sail.
If you're into the finer detail, here are the official specs, governing everything from wing design and layout to the type of GoPro cameras allowed on board.
Let's look at the pedal power.
It was a big decision to switch from traditional hand-powered 'grinders' (named after coffee grinders) and introduce pedal bays on the vessel.
Each team sails slightly differently and brings different power and technique. Motors are not allowed.
Team New Zealand have several innovations, not least the crew member at the front of the pedal bay being solely responsible for daggerboard adjustments and maintaining 'flight'.
That pedal system connects winch-like mechanics to hydraulic controls for moving the carbon fibre wingsail, rudders and the daggerboards. When you see the crew madly pedalling, the effect of all that leg power is moving hydraulic fluid around the vessel to the piston pumps (which look like this). The pumps attach to hydraulic cables, lines, and ropes to move the components.
The faster a crew can turn, moving the sail for instance across the vessel to catch the wind - moves called a 'tack' and a 'gybe' - the less travelling distance is lost and the faster they can cross the line.
Daggerboards can be moved in a number of ways.
'Raking' just means moving the L-shaped foils back towards the stern or forward to the bow, depending on the amount of lift needed to maintain stable flight.
Rear T-shaped rudders can be raked, but don't change height or move laterally.
The foils can also be moved up or down, and towards and away from the centre line, known as 'cant', which helps stabilise the craft, and contributes to 'righting movement'. This helps produce speed, because the more force and power applied to the catamaran's resistance to the wind, the faster it can travel. It's essentially a larger-scale version of solo sailing when you see sailors lean out over the water.
Legs can produce more power than arms and that power means the team adjust all the components of the catamaran extremely quickly.
Crucially, if you're pedalling, your hands are free to perform other tasks like tweak the foil rake, all adding up to crucial seconds.
The trick, when the hull lifts out of the water, is to keep the catamaran skimming across the surface about one metre above the water.
Because the yachts use rigid sails, rather than a cloth sail, the same principles of lift that apply to an aircraft are at work here - except on water.
It's basically an aircraft wing on water.
The sails have wide leading edges and thinner trailing edges and they're about the same size as a commercial aircraft wing. They're in two parts, and the crew can adjust the forward "lift" using a jib sail in the same way aircraft flaps are used.
An aircraft wing - or aerofoil - creates lift by taking advantage of the pressure difference on each side plus forward thrust from jet engines. Using the same principle, a sailing yacht with a fixed 'wingsail' gains forward motion using wind.
The sail shape means air travels faster over the back - or leeward - side. This difference in air speed creates lower pressure on the leeward side, higher pressure on the windward side, and "lifts" the sail forward over the water.
Angles can be adjusted to 'catch' the wind.
And the foils?
Water moves over the top surface of the foils - because of their aerodynamic shape and the forward thrust from the wingsail - faster than water on the lower surface. Where the water is faster, there isn't as much pressure, causing a difference in pressure and an upwards force.
When the hulls are out of the water, there is much less drag slowing the vessel down, so it skims over the water.
Above a certain speed, the upward lift overcomes drag and downward force, and the vessel moves upwards out of the water, then gains more speed and lots of adjustments are needed at this point to maintain balance.
Speed increases again when the foils are in use, as there is hardly anything in the water to create drag.
Physics can explain how and why the boats are so fast and manoeuvrable but it was the skill, speed, and intuition of Team New Zealand that gave them those crucial seconds against Team USA.