Why do boats sail faster downstream?

The boat should move a little sideways. In that “crab” movement, the keel moves through the water at an angle of attack. As with sails in the wind, this causes the water on the “higher (more downstream) side of the keel to move faster and creates lower pressure. The AC72s also use lift when thwarted, which is when the catamaran's two hulls rise out of the water and the boat is flying almost literally, with only the rudders and a board anchoring it to the bay.

Foiling makes the boat even faster because the drag forces that slow down the ship are now mostly in the air rather than in the water. Is it true that larger sailboats would have a faster top speed? With the wind blowing from behind and sailing perpendicular to the wind, a boat accelerates. The speed of the wind in the sail is the difference between the speed of advance of the ship and that of the wind. Once the boat reaches the same speed as the wind, it's impossible to go any faster.

But with the wind blowing from the front, the ship turns its sails towards the wind about 45°. The sails deflect the wind slightly as it blows through them, which slows down the wind and exerts a lateral force on the sail. The keel (the large fin that extends below the hull) cancels lateral force. But, if the sail is tilted correctly, part of that force also propels the boat forward.

The boat continues to accelerate until that force is equalized by the drag of the water. Therefore, with aerodynamic and intelligent hull designs, a boat can sail faster than the wind. If a boat sails absolutely perpendicular to the true wind, so the sail is flat to the wind and is pushed from behind, then the boat can only go as fast as the wind not faster. If the downwind speed component is greater than the wind speed, then in the frame of the ship it appears that the ship is sailing towards the wind.

The faster the ship goes, the greater the relative wind, the more force there is in the sails, so the greater the force that drags the ship forward. If the wind is 10 kt and the boat is 6 kt in the same direction, the crew feels a 4 kt wind coming from the stern of the boat.