America's Cup: What makes Team New Zealand's boat go so fast?

Emirates Team New Zealand competes on the second day of the best-of-nine America's Cup challenger finals on Bermuda's Great Sound, Sunday. Photo / AP

As Emirates Team New Zealand prepares to take on Oracle Team USA in the America's Cup finals series this weekend, we take a look at who and what makes the black boat go so fast.

All the America's Cup boats have to follow the same design for the size and shape of their sails, their twin hulls and the cross members that connect the hulls.

But each team can decide how to control the sail and within certain rules, the design of the foils that send the boats flying up out of the water.

The cyclors

The teams biggest innovation - now partly copied by Oracle - was the introduction of "cyclors" (sailors riding small on-board bikes) rather than grinders to power the boat's hydraulics, which control the wing sail.

As legs are stronger than arms, this gives the crew more power, although critics say it makes it harder to move quickly from one side of the boat to the other.