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
Wind assistance have been rare. Tatyana Chernova greatly outperformed the current world junior record of 6542 points with a wind-assisted score of 6768 points in June 2007 in Arles, France. Other wind-assisted series from Arles were recorded in 1987 and 2006. There is no wind speed rule for road events, but the start and finish points of a course, measured along a theoretical straight line between them, shall not be further apart than 50% of the race distance to be allowed as a record. This is due to the wind advantage that might take place for a straight course. The Athens Classic