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 Australia southern coastline lies in the roaring forties and hundreds of sites have average wind speeds above 8 or even 9 m/s at 50 m above ground (the hub height of a modern wind generator). The southwest of Western Australia, southern South Australia, western Victoria, northern Tasmania and elevated areas of New South Wales and Queensland have good wind resources. Several states engaged in systematic wind speed monitoring in the 1980s and 1990s, the results of which are publicly available. Australian wind farms produce on average capacity factors of 30–35%, making wind an attractive option. South Australia's large share (along with