Apparently this is what the car feels.

Ac75 apparent wind. The AC75 is a completely new class and two years ago. In 12-15 knots of wind these amazing sailboats have reached speeds in excess of 50 knots. The AC75 rudders are very small and the crews need to balance steering and trimming accurately not to lose control.

As the car speeds up the wind increases in velocity and the direction of origin feels like it moves forward. If you stop the car the apparent wind goes back to. So same on a boat.

In mere seconds the AC75 goes from low-speed displacement sailing in as little as 10 knots apparent wind speed to high-speed foiling in excess of 50 knots apparent wind speed. The wind that the car feels is the shifted wind called the apparent wind. The AC75 is not expected to be foiling until windpeeds of 9kts while its predecessor the AC50 could sail at four times the speed of the wind at just 6kts of breeze.

AC75 Class Rule 1210 Proposed amendment. On the flipside the same effect may mean the trailing boat needs a bigger wind shadow to slow it down so the effects could cancel out. To do that on the wings you invert the top of the sail create negative camber which provides righting moment as the apparent wind forces the top of the rig to windward.

The variance in strength and direction raises the issue of why race organisers are even bothering with the potential TV stopping tidal flow complication - given that the AC75s are sailing in an apparent wind of up to 60kts and a knot or so of tidal effect on the race boats is going to be negligible. It is the wind shifting forward as a car accelerates. One of the biggest innovations for the new AC75 Americas Cup boat is the soft wingsail.

AC75 capable of 5x windspeed - apparent wind angle 115 deg AC50 capable of 4x windspeed - apparent wind angle 143 deg windsurfer and blokart and AC62 capable of 3x windspeed - apparent wind angle 191 deg. Although the boats will be foiling most of the time it is going to be incredibly important to have a hull which gets you foiling as quickly as possible Bernasconi says. But once the boat is foiling the apparent wind speed and angle will change dramatically.