Apparent wind that measures wind speed in knots and wind direction in degrees relative to the heading of the boat. Modern instrumentation can calculate the true wind velocity when the apparent wind and boat speed and direction are input. In sailboat racing, and especially in speed sailing, apparent wind is a vital factor, when determining the points of sail a sailboat can effectively travel in. A vessel traveling at increasing speed relative to the "prevailing wind" will encounter the wind driving the sail at a decreasing angle and increasing velocity. Eventually, the increased drag and diminished degree of efficiency of a sail
Apparent wind of the true wind" minus the "velocity of the object". In sailing, "apparent wind" is the speed and direction of wind indicated by a wind instrument (anemometer) on a "moving" craft (on water, land or ice) in undisturbed air. It is composed of the "combined" speeds and directions of the craft and wind observed by a "stationary" wind instrument—the "true wind". A true wind coming from the bow increases the apparent wind induced by the speed of the craft, coming from the stern it decreases apparent wind, and coming from the side the apparent wind angle and speed change according