Editing Apparent wind (section)

==Implications on sailing speeds==
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 at extremely low [[Angle of attack|angles]] will cause a loss of accelerating force. This constitutes the main limitation to the speed of wind-driven vessels and vehicles.{{cn|date=September 2016}}

[[windsurfing|Windsurfers]] and certain types of boats are able to sail faster than the true wind. These include fast [[multihull]]s and some [[Planing (sailing)|planing]] monohulls.  [[ice yachting|Ice-sailors]] and [[land sailing|land-sailors]] also usually fall into this category, because of their relatively low amount of [[drag (physics)|drag]] or [[friction]].{{cn|date=September 2016}}

The AC72 foiling catamarans used in the America's Cup are an example of this phenomenon, as the boats sail through the water at up to double the environmental wind speed. The effect of this is to radically change the apparent wind direction when sailing "downwind". In these boats the forward speed is so great that the apparent wind is always forward—at an angle that varies between 2 and 4 degrees to the wing sail. This means that AC72's  are effectively tacking downwind, although at a greater angle than the normal 45-degree upwind angle, usually between 50 and 70 degrees.<ref>TVNZ Live America's cup Broadcast. Interview with Tom Schnackenburg. 22/9/2013</ref>