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
Variable speed wind turbine length of the blade, formula_4 is the velocity of the wind, and formula_5 is the power coefficient for the wind turbine. The power coefficient is a representation of how much of the available power in the wind is captured by the wind turbine. The torque, formula_15, on the blades is given by the ratio of the power extracted to the rotor speed, formula_2: formula_17 The rotor speed can be related to the wind speed, formula_4, through the tip-speed ratio, formula_6: formula_1 Thus we can get the following expressions for torque and power: formula_21 and formula_22 From the above equation, we