If the sail creates a sideways force, why doesn’t the boat just slide sideways? The answer is the (or centerboard) under the boat.
There is a "No-Go Zone" (usually about 45 degrees on either side of the wind). If you point the bow too close to the wind, the air can no longer flow smoothly over both sides of the sail. The sail "stalls," loses its wing-like properties, and begins to flap like a flag. Physics of Sailing
Sailing is essentially a game of "aerodynamic tug-of-war" between the air above the water and the water below it. 1. The Sail as a Wing (Lift) If the sail creates a sideways force, why
If the sail’s force is too far back, the boat will naturally want to turn the wind (weather helm). If you point the bow too close to
The boat "squeezes" between the wind’s push and the water’s resistance, converting that sideways energy into forward motion—much like a wet bar of soap shooting out of your hand when you squeeze it. 3. Apparent Wind
The keel provides a massive amount of "lateral resistance." It is very hard to push a large flat fin sideways through water, but very easy to move it forward.
Like an airplane wing, a curved sail creates a pressure difference. Air travels faster over the "outer" (leeward) curve of the sail, creating low pressure. Higher pressure on the inside pushes the sail toward that low-pressure zone.
