V = boat speed, H = head wind, W = true wind, A = apparent wind, a = pointing angle, b = angle of apparent wind

Apparent wind is the wind relative to a moving object. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Apparent wind in sailing

In sailing, the apparent wind is the actual flow of air acting upon a sail, or the wind as it appears to the sailor. It differs from the true or prevailing wind seen by a stationary observer in velocity and direction. In nautical terminology, these properties of the apparent wind are expressed in knots and degrees. For either of the songs named Sailing, see Sailing (song). ... This is a glossary of nautical terms; some remain current, many date from the 17th-19th century. ... A knot is a unit of speed abbreviated kt or kn. ... This article describes the unit of angle. ...

Definition of apparent wind

Apparent wind is the vector sum of the True Wind Velocity and the air stream generated by an "object's Velocity over ground". This is the Inverse (mathematics) of the objects actual velocity or more succinctly the apparent wind is defined as the Velocity of the wind minus the Velocity of the object. A vector in physics and engineering typically refers to a quantity that has close relationship to the spatial coordinates, informally described as an object with a magnitude and a direction. The word vector is also now used for more general concepts (see also vector and generalizations below), but in this... This article or section does not adequately cite its references or sources. ... In physics, velocity is defined as the rate of change of displacement or the rate of displacement. ... Inverse is the opposite of something. ...

Calculating velocity and angle

Where:

• H = head wind
• W = true wind velocity
• a = true pointing angle in degrees (0 = upwind, 180 = downwind)
• A = apparent wind velocity

The angle of apparent wind (b) can be deducted from the measured boat and wind speeds using the inverse cosine in degrees (AcosD)

Instruments

The apparent wind on-board is often quoted as a speed measured by a masthead transducer containing an anemometer and wind vane 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 velocity are input. A masthead refers to the top of a mast of a ship. ... A transducer is a device, usually electrical or electronic, that converts one type of energy to another. ... Cup-type anemometer with vertical axis and turnabout counter located at the Dübendorf museum of military aviation An anemometer is a device for measuring the velocity or the pressure of the wind, and is one instrument used in a weather station. ... Weather vane Weather cock Aerovane A weather vane, also called a wind vane, is a movable device attached to an elevated object such as a roof for showing the direction of the wind. ... A knot is a unit of speed abbreviated kt or kn. ... A course, in navigation, is the direction of travel. ...

Implications on sailing speeds

In sailboat racing, and especially in speed sailing, apparent wind is a vitally important factor, when determining the points of sail a sail-boat can effectively travel in. A vessel travelling 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 angles will cause a loss of accelerating force. This constitutes the main limitation to the speed of wind-driven vessels and vehicles. Inshore yacht racing on Sydney Harbour, Australia Yacht racing is the sport of competitive sailing. ... Speed sailing is the art of sailing a craft as fast as possible over a predetermined route, and having its overall or peak speed recorded and accredited by a regulatory body. ... Points of sail is the term used to describe a sailing boats course in relation to the wind direction. ... In this diagram, the black arrow represents the direction of the wind. ...

Windsurfers and certain types of boats are able to sail faster than the true wind. These include fast multihulls and some planing monohulls. Ice-sailors and land-sailors also usually fall into this category, because of their relatively low amount of drag or friction. A windsurfer with modern gear tilts the rig and carves the board to perform a planing gybe (downwind turn) close to shore in Maui, Hawaii, one of the popular destinations for windsurfing. ... A multihull is a ship or boat with more than one hull. ... A Musto Skiff, planing on a fast reach A planing boats hull skims across the surface of the water rather than pushing through the water in the way a traditional displacement hull works. ... Ice yachting is the sport of sailing and racing iceboats, also called ice yachts. ... It has been suggested that this article or section be merged with Land yacht. ... Look up Drag in Wiktionary, the free dictionary. ... friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. ...

Other areas of relevance

In fixed-wing aircraft, apparent wind is what is experienced on-board and it determines the necessary speeds for take-off and landing. Aircraft carriers generally steam directly upwind at maximum speed, in order to increase apparent wind and reduce the necessary take-off velocity. Land-based airport traffic generally take off and land facing upwind for the same reason. This article needs additional references or sources for verification. ... Four aircraft carriers, (bottom-to-top) Principe de Asturias, amphibious assault carrier USS Wasp, supercarrier USS Forrestal and light V/STOL carrier HMS Invincible, showing size differences of late 20th century carriers An aircraft carrier is a warship designed to deploy and recover aircraft — in effect acting as a sea...