It appears spontaneous that sailboats, driven purely by the blowing wind, can travel easily with the breeze at their backs, however it may appear difficult that they turn around and come home again, with the wind power blowing directly towards them.
Yet this opposite movement is achievable since a moving boat’s sail is designed as an airfoil – similar to the wing of a plane. Whenever air moves over a plane’s wing, via front to back, wind flowing over the top part of the wing needs to travel farther than wind moving underneath the wing’s base surface. This produces a pressure distinction that pulls the plane.
On a sailboat, wind flow blowing contrary to the boat at an angle expands the sail, and it forms an identical foil shape, resulting in a difference in pressure that presses the sail perpendicular to the wind flow direction.
Based on “The Physics of Sailing Explained” by Kent State University physics instructor Bryon D. Anderson, this kind of force from the sail’s foil pattern is merged with and balanced by other forces, as well as those of the boat’s keel (the lengthy thin element that juts down from the base of the boat).
Together, the forces of drag, out of the water, and the force from the wind against the sail alone push the craft onward. It proceeds at an angle reverse to the path of the wind, called windward in sailing vocabulary.
In accordance to the American Institute of Physics’ Physics Today journal, the keel is particularly significant simply because without its balancing motion, a boat could basically drift downwind.
Windward sailing as well doesn’t work if a boat is aimed directly reverse the wind flow direction, according to The Physics of Sailing. Wind flow has to be shifting contrary to the boat at an angle for a minimum of 40 degrees for some vessels. Angling far too sharply into the blowing wind triggers the forces on the boat to become out of balance, and flows the boat sideways in the water.
A sailor aiming to travel windward toward a point accurately in line with the path of the wind flow will have to zig-zag forward and backward to attain its target. By using this “tacking” approach, and traveling at a position as near towards the wind’s route as possible, sailors can get to a place in any direction, irrespective of the direction of the blowing wind.
