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 power in Thailand resource map with 13 year-long data (1966-1978) from 53 wind speed measurement stations of the TMD, using power law to standardize all wind speed to 10 m. In 1984, another similar attempt was carried out by KMITT, using 17 year-long (1966-1982) data from 62 measurement stations, and with financial support from USAID. Attempts at producing wind resource maps of Thailand all faced the problem of shortage in wind speed data, especially offshore and at high elevations. This resulted in maps with low coverage. In 2001, another set of wind resource maps was produced by DEDE using data from over 150