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Sailing employs the wind—acting on
sail A sail is a tensile structure by Vladimir Shukhov (during construction), Nizhny Novgorod, 1895 in Kings Domain, Melbourne A tensile structure is a construction of elements carrying only tension (physics), tension and no compression (physical ...
s,
wingsail A wingsail, twin-skin sail or double skin sail is a variable-Camber (aerodynamics), camber aerodynamic structure that is fitted to a marine vessel in place of conventional sails. Wingsails are analogous to Wing, airplane wings, except that they a ...
s or
kite A kite is a tether A tether is a cord, fixture, or flexible attachment that characteristically anchors something movable to something fixed; it also maybe used to connect two movable objects, such as an item being towing, towed by its tow. ...

kite
s—to propel a craft on the surface of the ''water'' (
sailing ship A sailing ship is a sea-going vessel that uses sail A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboat sloop ged sloop Image:Sa ...

sailing ship
,
sailboat sloop ged sloop Image:Sail plan sloop.svg, Gaff-rigged sloop with a Topsail#Gaff rig, gaff topsail A sloop is a sailboat with a single mast (sailing), mast typically having only one headsail in front of the mast and one mainsail aft of (behind ...

sailboat
,
windsurfer Windsurfing is a surface water sport that is a combination of surfing and sailing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the surf culture of California. Windsurfing had gained a following ...

windsurfer
, or
kitesurfer Kiteboarding or kitesurfing is an extreme sport where the kiter uses the wind power with a large power kite to be pulled on a water, land or snow surface. It combines aspects of paragliding, surfing, windsurfing, skateboarding, snowboarding and ...

kitesurfer
), on ''ice'' (
iceboat An iceboat (occasionally spelled ice boat or traditionally called an ice yacht) is a recreational or competition sailing craft supported on metal runners for traveling over ice. One of the runners is steerable. Originally, such craft were boats ...

iceboat
) or on ''land'' (
land yacht Land sailing, also known as 'sand yachting', 'land yachting' or 'dirtboating', is the act of moving across land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughou ...
) over a chosen
course Course may refer to: Directions or navigation * Course (navigation), the path of travel * Course (orienteering), a series of control points visited by orienteers during a competition, marked with red/white flags in the terrain, and corresponding ...

course
, which is often part of a larger plan of
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

navigation
. Until the middle of the 19th century, sailing ships were the primary means for marine exploration, commerce, and projection of military power; this period is known as the
Age of Sail Age or AGE may refer to: Time and its effects * Age, the amount of time something has been alive Alive may refer to: *Life Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling a ...

Age of Sail
. In the 21st century, most sailing represents a form of
recreation Recreation is an activity of leisure Leisure has often been defined as a quality of experience or as free time. Free time is spent away from , , , , and , as well as necessary activities such as and ing. Leisure as an experience usuall ...

recreation
or
sport Sport pertains to any form of competitive Competition is a rivalry A rivalry is the state of two people or groups engaging in a lasting competitive relationship. Rivalry is the "against each other" spirit between two competing sides. ...
.
Recreational sailing
Recreational sailing
or
yachting Yachting is the use of recreational boats and ships called ''yacht A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies to such vessels that have a cabin with amenit ...
can be divided into
racing In sport, racing is a competition of speed, against an objective criterion, usually a clock or to a specific point. The competitors in a race try to complete a given task in the shortest amount of time. Typically this involves :wikt:traverse, tra ...
and
cruising Cruising may refer to: * Cruising, on a cruise ship *Cruising (driving), driving around for social purposes, especially by teenagers *Cruising (maritime), leisurely travel by boat, yacht, or cruise ship *Cruising for sex, the process of searching i ...
. Cruising can include extended offshore and ocean-crossing trips, coastal sailing within sight of land, and daysailing. Sailing relies on the physics of sails as they derive power from the wind, generating both lift and drag. On a given course, the sails are set to an angle that optimizes the development of wind power, as determined by the
apparent wind 325px, V = boat speed, H = head wind, W = true wind, A = apparent wind, α = pointing angle, β = angle of apparent wind Apparent wind is the wind experienced by a moving object. Definition of apparent wind The ''apparent wind'' is the wind exper ...
, which is the wind as sensed from a moving vessel. The forces transmitted via the sails are resisted by forces from the
hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a ship * Submarine hull Mathematics * Affine hull, in affin ...
,
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...

keel
, and
rudder A rudder is a primary control surface used to steer a ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep Sea lane, waterways, carrying goods or passengers, or in support of specialized missions, su ...

rudder
of a sailing craft, by forces from skate runners of an iceboat, or by forces from wheels of a land sailing craft to allow steering the course. This combination of forces means that it is possible to sail an upwind course as well as downwind. The course with respect to the true wind direction (as would be indicated by a stationary flag) is called a
point of sail A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface. The principal points of sail roughly correspond to 45° segments of a circle, starting with 0° directly into the wind. ...

point of sail
. Conventional sailing craft cannot derive wind power on a course with a point of sail that is too close into the wind.


History

Throughout history sailing has been a key form of propulsion that allowed greater mobility than travel over land, whether for exploration, trade, transport, or warfare, and that increased the capacity for fishing, compared to that from shore. Early square rigs generally could not sail much closer than 80° to the wind, whereas early fore-and-aft rigs could sail as close as 60–75° off the wind. Later square-rigged vessels too were able to sail to windward, and became the standard for European ships through the Age of Discovery when vessels ventured around Africa to India, to the Americas and around the world. Sailing ships became longer and faster over time, with ship-rigged vessels carrying taller masts with more square sails. The
Age of Sail Age or AGE may refer to: Time and its effects * Age, the amount of time something has been alive Alive may refer to: *Life Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling a ...

Age of Sail
(1570–1870) reached its peak in the 18th and 19th centuries with merchant sailing ships that were able to travel at speeds that exceeded those of the newly introduced
steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel Steam-powered vessels include steamboats and steamships. Smaller steamboats were developed first. They were replaced by larger steamships which were often ocean-going. ...

steamship
s.


Exploration and research

Austronesian peoples The Austronesian peoples, also sometimes referred to as the Austronesian-speaking peoples, are a large group of various peoples in Taiwan Taiwan (), officially the Republic of China (ROC), is a country in East Asia. Neighbouring countries ...
sailed from what is now Southern China and
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and N ...

Taiwan
with of
Catamaran A Formula 16 beachable catamaran Powered catamaran passenger ferry at Salem, Massachusetts, United States A catamaran () (informally, a "cat") is a multi-hulled watercraft Watercraft, also known as water vessels or waterborne vessels, a ...

Catamaran
s or vessels
outriggers An outrigger is a projecting structure on a boat, with specific meaning depending on types of vessel. Outriggers may also refer to legs on a wheeled vehicle that are folded out when it needs stabilization, for example on a crane (machine), cra ...
, and crab claw sails, which enabled the
Austronesian Expansion The Austronesian peoples, also sometimes referred to as the Austronesian-speaking peoples, are a large group of various peoples in Taiwan (collectively known as Taiwanese indigenous peoples), Maritime Southeast Asia, Oceania and Madagascar that ...
at around 3000 to 1500 BCE into the islands of
Maritime Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, East Timor, Indonesia, Malaysia, Papua New Guinea, the Philippines and Singapore. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia ...
, and thence to
Micronesia Micronesia (, ; from grc, μικρός ''mikrós'' "small" and ''nêsos'' "island") is a subregion of Oceania, consisting of thousands of small islands in the western Pacific Ocean. It has a close shared cultural history with three other isl ...

Micronesia
,
Island MelanesiaIsland Melanesia is a subregion of Melanesia in Oceania Oceania (, , ) is a geographic region that includes Australasia, Melanesia, Micronesia and Polynesia. Spanning the Eastern and Western Hemispheres, Oceania has a land area of and a p ...
,
Polynesia Polynesia (, ; from grc, πολύς "many" and grc, νῆσος "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; fj, Kai-Polinesia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia) is a ...

Polynesia
, and
Madagascar Madagascar (; mg, Madagasikara), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), and previously known as the Malagasy Republic The Malagasy Republic ( mg, Repoblika Mala ...

Madagascar
. They traveled vast distances of open ocean in
outrigger canoe Outrigger boats are various watercraft featuring one or more lateral support floats known as outriggers, which are fastened to one or both sides of the main hull (ship), hull. They can range from small dugout (boat), dugout canoes to large plank ...
s using navigation methods such as stick charts. By the time of the
Age of Discovery The Age of Discovery, or the Age of Exploration (sometimes also, particularly regionally, Age of Contact or Contact Period), is an informal and loosely defined term for the early modern period approximately from the 15th century to the 18th century ...
—starting in the 15th century—square-rigged, multi-masted vessels were the norm and were guided by navigation techniques that included the magnetic compass and making sightings of the sun and stars that allowed transoceanic voyages. During the Age of Discovery, sailing ships figured in European voyages around Africa to China and Japan; and across the Atlantic Ocean to North and South America. Later, sailing ships ventured into the Arctic to explore northern sea routes and assess natural resources. In the 18th and 19th centuries sailing vessels made
Hydrographic survey ''Neptune'', a privately owned Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates = , coordinates_footnotes = , subdivi ...
s to develop charts for navigation and, at times, carried scientists aboard as with the voyages of
James Cook Captain Captain is a title for the commander of a military unit, the commander of a ship, aeroplane, spacecraft, or other vessel, or the commander of a port, fire department or police department, election precinct, etc. The captain is a milit ...

James Cook
and the Second voyage of HMS ''Beagle'' with naturalist
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all sp ...

Charles Darwin
.


Commerce

In the early 1800s, fast blockade-running schooners and brigantines—
Baltimore Clipper A Baltimore Clipper is a fast sailing ship historically built on the mid-Atlantic seaboard of the United States of America, especially at the port of Baltimore, Maryland. An early form of clipper, the name is most commonly applied to two-masted ...
s—evolved into three-masted, typically ship-rigged sailing vessels with fine lines that enhanced speed, but lessened capacity for high-value cargo, like tea from China. Masts were as high as and were able to achieve speeds of , allowing for passages of up to per 24 hours. Clippers yielded to bulkier, slower vessels, which became economically competitive in the mid 19th century. Sail plans with just fore-and-aft sails (
schooner A schooner () is a type of defined by its rig: on all of two or more masts and, in the case of a two-masted schooner, the foremast generally being shorter than the mainmast. A common variant, the topsail schooner also has a square topsail on th ...

schooner
s), or a mixture of the two (
brigantine A brigantine is a two-masted sailing vessel with a fully square-rig Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square In E ...

brigantine
s,
barque A barque, barc, or bark is a type of sailing vessel A sailing ship is a sea-going vessel that uses sails mounted on Mast (sailing), masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailin ...

barque
s and
barquentine A barquentine or schooner barque (alternatively "barkentine" or "schooner bark") is a sail A sail is a tensile structure by Vladimir Shukhov (during construction), Nizhny Novgorod, 1895 in Kings Domain, Melbourne A tensile structure is a ...
s) emerged. Coastal top-sail schooners with a crew as small as two managing the sail handling became an efficient way to carry bulk cargo, since only the fore-sails required tending while tacking and steam-driven machinery was often available for raising the sails and the anchor.
Iron-hulled sailing ship 300px, Four-masted, iron-hulled barque ''Herzogin Cecilie''">Herzogin_Cecilie.html" ;"title="barque ''Herzogin Cecilie">barque ''Herzogin Cecilie'' Iron-hulled sailing ships represented the final evolution of sailing ships at the end of the age of ...
s represented the final evolution of sailing ships at the end of the Age of Sail. They were built to carry bulk cargo for long distances in the nineteenth and early twentieth centuries. They were the largest of merchant sailing ships, with three to five masts and square sails, as well as other
sail plan A sail plan is a description of the specific ways that a sailing craft is rigged. Also, the term "sail plan" is a graphic depiction of the arrangement of the sails for a given sailing craft.> Introduction A well-designed sail plan should b ...

sail plan
s. They carried bulk cargoes between continents. Iron-hulled sailing ships were mainly built from the 1870s to 1900, when
steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel Steam-powered vessels include steamboats and steamships. Smaller steamboats were developed first. They were replaced by larger steamships which were often ocean-going. ...

steamship
s began to outpace them economically, due to their ability to keep a schedule regardless of the wind. Steel hulls also replaced iron hulls at around the same time. Even into the twentieth century, sailing ships could hold their own on transoceanic voyages such as Australia to Europe, since they did not require bunkerage for coal nor fresh water for steam, and they were faster than the early steamers, which usually could barely make . Ultimately, the steamships' independence from the wind and their ability to take shorter routes, passing through the
Suez Suez ( ar, السويس '; ) is a Port#Seaport, seaport city (population of about 750,000 ) in north-eastern Egypt, located on the north coast of the Gulf of Suez (a branch of the Red Sea), near the southern terminus of the Suez Canal, having ...
and
Panama Canal The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a List of transcontinental countries#Nor ...

Panama Canal
s, made sailing ships uneconomical.


Naval power

Until the general adoption of carvel-built ships that relied on an internal skeleton structure to bear the weight of the ship and for gun ports to be cut in the side, sailing ships were just vehicles for delivering fighters to the enemy for engagement. By 1500,
Gun port A gunport is an opening in the side of the hull (watercraft), hull of a ship, above the waterline, which allows the muzzle of artillery pieces mounted on the gun deck to fire outside. The origin of this technology is not precisely known, but can be ...
s allowed sailing vessels to sail alongside an enemy vessel and fire a
broadside ship of the line A ship of the line was a type of naval warship constructed during the Age of Sail from the 17th century to the mid-19th century. The ship of the line was designed for the naval tactics in the Age of Sail, naval tactic known as ...
of multiple cannon. This development allowed for naval fleets to array themselves into a
line of battle In naval warfare Naval warfare is human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, lang ...
, whereby,
warships A warship or combatant ship is a naval ship A naval ship is a military (or sometimes , depending on classification) used by a . Naval ships are differentiated from civilian ships by construction and purpose. Generally, naval ships ar ...
would maintain their place in the line to engage the enemy in a parallel or perpendicular line.


Modern applications

While the use of sailing vessels for commerce or naval power has been supplanted with engine-driven vessels, there continue to be commercial operations that take passengers on sailing cruises. Modern navies also employ sailing vessels to train cadets in
seamanship Seamanship is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ideas. There is no generally agreed definition of wha ...
. Recreation or sport accounts for the bulk of sailing in modern boats.


Recreation

Recreational sailing can be divided into two categories, day-sailing, where one gets off the boat for the night, and cruising, where one stays aboard. Day-sailing primarily affords experiencing the pleasure of sailing a boat. No destination is required. It is an opportunity to share the experience with others. A variety of boats with no overnight accommodations, ranging in size from to over , may be regarded as day sailors. Cruising on a sailing yacht may be either near-shore or passage-making out of sight of land and entails the use of sailboats that support sustained overnight use. Coastal cruising grounds include areas of the Mediterranean and Black Seas, Northern Europe, Western Europe and islands of the North Atlantic, West Africa and the islands of the South Atlantic, the Caribbean, and regions of North and Central America. Passage-making under sail occurs on routes through oceans all over the world. Circular routes exist between the Americas and Europe, and between South Africa and South America. There are many routes from the Americas, Australia, New Zealand, and Asia to island destinations in the South Pacific. Some cruisers
circumnavigate File:2010 09 05 Planit Solar 1.JPG, 300px, In 2012, the Swiss boat ''Tûranor PlanetSolar, PlanetSolar'' became the first ever solar electric vehicle to circumnavigate the globe. Circumnavigation is the complete navigation around an entire islan ...
the globe.


Sport

Sailing as a sport is organized on a hierarchical basis, starting at the
yacht club A yacht club is a sports club 250px, A sport club in Belo Horizonte, Brazil, showing various paved and painted surfaces for futsal">Brazil.html" ;"title="Belo Horizonte, Brazil">Belo Horizonte, Brazil, showing various paved and painted sur ...

yacht club
level and reaching up into national and international federations; it may entail , sailing dinghies, or other small, open sailing craft, including iceboats and land yachts.
Sailboat racing The sport of sailing involves a variety of competitive sailing Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' (sailing ship, sailboat, Windsurfing, windsurfer, or Kitesurfi ...
is governed by
World Sailing World Sailing (WS) is the world governing body for the sport of sailing recognized by the International Olympic Committee The International Olympic Committee (IOC; french: Comité international olympique, CIO) is a non-governmental Sport ...
with most racing formats using the
Racing Rules of Sailing The Racing Rules of Sailing (often abbreviated to RRS) govern the conduct of yacht racing, windsurfing, kitesurfing, model boat racing, dinghy racing and virtually any other form of racing around a course with more than one vessel while powered ...
. It entails a variety of different disciplines, including: *Oceanic racing, held over long distances and in open water, often last multiple days and include world
circumnavigation 300px, In 2012, the Swiss boat '' PlanetSolar'' became the first ever solar electric vehicle to circumnavigate the globe. Circumnavigation is the complete navigation around an entire island, continent, or astronomical object, astronomical body ...
, such as the and
The Ocean Race The Ocean Race is a yacht A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies to such vessels that have a cabin with amenities that accommodate overnight use. To be ...
. *Fleet racing, featuring multiple boats in a
regatta A regatta is a series of boat races. The term comes from the Venetian language regata meaning "contest" and typically describes racing events of Rowing (sport), rowed or sailing (sport), sailed water craft, although some powerboat race series ...

regatta
that comprises multiple races or heats. *Match racing comprises two boats competing against each other, as is done with the
America's Cup The America's Cup, informally known as the Auld Mug, is a trophy A trophy is a tangible, durable reminder of a specific achievement, and serves as a recognition or evidence of merit. Trophies are often awarded for , from youth sports to pr ...

America's Cup
, vying to cross a finish line, first. *Team racing between two teams of three boats each in a format analogous to match racing. *Speed sailing to set new
records A record, recording or records may refer to: An item or collection of data Computing * Record (computer science) In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures ...
for different categories of craft with oversight by the
World Sailing Speed Record Council The World Sailing Speed Record Council (WSSRC) was founded in 1972, initially to ratify records at the inaugural Weymouth Speed Week held every year since in Portland Harbor.The WSSRC is the body authorized by the World Sailing (formerly Internation ...
. *Sail boarding has a variety of disciplines particular to that sport.


Navigation


Point of sail

A sailing craft's ability to derive power from the wind depends on the
point of sail A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface. The principal points of sail roughly correspond to 45° segments of a circle, starting with 0° directly into the wind. ...

point of sail
it is on—the direction of travel under sail in relation to the true wind direction over the surface. The principal points of sail roughly correspond to 45° segments of a circle, starting with 0° directly into the wind. For many sailing craft, the arc spanning 45° on either side of the wind is a "no-go" zone, where a sail is unable to mobilize power from the wind. Sailing on a course as close to the wind as possible—approximately 45°—is termed "close-hauled". At 90° off the wind, a craft is on a "beam reach". At 135° off the wind, a craft is on a "broad reach". At 180° off the wind (sailing in the same direction as the wind), a craft is "running downwind". In points of sail that range from close-hauled to a broad reach, sails act substantially like a wing, with lift predominantly propelling the craft. In points of sail from a broad reach to down wind, sails act substantially like a parachute, with drag predominantly propelling the craft. For craft with little forward resistance, such as
ice boat An iceboat (occasionally spelled ice boat or traditionally called an ice yacht) is a recreational or competition sailing craft supported on metal runners for traveling over ice. One of the runners is steerable. Originally, such craft were boats ...
s and
land yacht Land sailing, also known as 'sand yachting', 'land yachting' or 'dirtboating', is the act of moving across land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughou ...
s, this transition occurs further off the wind than for
sailboat sloop ged sloop Image:Sail plan sloop.svg, Gaff-rigged sloop with a Topsail#Gaff rig, gaff topsail A sloop is a sailboat with a single mast (sailing), mast typically having only one headsail in front of the mast and one mainsail aft of (behind ...

sailboat
s and
sailing ship A sailing ship is a sea-going vessel that uses sail A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboat sloop ged sloop Image:Sa ...

sailing ship
s. Wind direction for points of sail always refers to the ''true wind''—the wind felt by a stationary observer. The ''
apparent wind 325px, V = boat speed, H = head wind, W = true wind, A = apparent wind, α = pointing angle, β = angle of apparent wind Apparent wind is the wind experienced by a moving object. Definition of apparent wind The ''apparent wind'' is the wind exper ...
''—the wind felt by an observer on a moving sailing craft—determines the
motive power ''Motive Power'' is a bi-monthly railway related magazine that focuses on diesel locomotives in Rail transport in Australia, Australia. The first issue was published on 23 August 1998. Its headquarters is in Sydney. The content includes photograp ...
for sailing craft.
;A sailboat on three points of sail The waves give an indication of the ''true wind'' direction. The flag gives an indication of ''apparent wind'' direction.
File:Shrike-port-beam.jpg, ''Close-hauled'': the flag is streaming backwards, the sails are sheeted in tightly. File:Shrike-reaching.jpg, ''Reaching'': the flag is streaming slightly to the side as the sails are sheeted to align with the apparent wind. File:Shrike-running.jpg, ''Running'': the wind is coming from behind the vessel; the sails are "wing on wing" to be at right angles to the apparent wind.


Effect on apparent wind

True wind velocity (VT) combines with the sailing craft's velocity (VB) to be the ''apparent wind velocity'' (VA), the air velocity experienced by instrumentation or crew on a moving sailing craft. Apparent wind velocity provides the motive power for the sails on any given point of sail. It varies from being the true wind velocity of a stopped craft in irons in the no-go zone to being faster than the true wind speed as the sailing craft's velocity adds to the true windspeed on a reach, to diminishing towards zero, as a sailing craft sails dead downwind.
;Effect of apparent wind on sailing craft at three points of sail Sailing craft A is close-hauled. Sailing craft B is on a beam reach. Sailing craft C is on a broad reach.
Boat velocity (in black) generates an equal and opposite apparent wind component (not shown), which adds to the true wind to become apparent wind.
File:Forces on sails for three points of sail.jpg, Apparent wind and forces on a ''sailboat''.
As the boat sails further from the wind, the apparent wind becomes smaller and the lateral component becomes less; boat speed is highest on the beam reach. File:Ice boat apparent wind on different points of sail.jpg, Apparent wind on an ''iceboat''.
As the iceboat sails further from the wind, the apparent wind increases slightly and the boat speed is highest on the broad reach. The sail is sheeted in for all three points of sail.
The speed of sailboats through the water is limited by the resistance that results from hull drag in the water. Ice boats typically have the least resistance to forward motion of any sailing craft. Consequently, a sailboat experiences a wider range of apparent wind angles than does an ice boat, whose speed is typically great enough to have the apparent wind coming from a few degrees to one side of its course, necessitating sailing with the sail sheeted in for most points of sail. On conventional sailboats, the sails are set to create lift for those points of sail where it's possible to align the leading edge of the sail with the apparent wind. For a sailboat, point of sail affects lateral force significantly. The higher the boat points to the wind under sail, the stronger the lateral force, which requires resistance from a keel or other underwater foils, including daggerboard, centerboard, skeg and rudder. Lateral force also induces heeling in a sailboat, which requires resistance by weight of ballast from the crew or the boat itself and by the shape of the boat, especially with a catamaran. As the boat points off the wind, lateral force and the forces required to resist it become less important. On ice boats, lateral forces are countered by the lateral resistance of the blades on ice and their distance apart, which generally prevents heeling.


Course under sail

Wind and currents are important factors to plan on for both offshore and inshore sailing. Predicting the availability, strength and direction of the wind is key to using its power along the desired course. Ocean currents, tides and river currents may deflect a sailing vessel from its desired course. If the desired course is within the no-go zone, then the sailing craft must follow a zig-zag route into the wind to reach its waypoint or destination. Downwind, certain high-performance sailing craft can reach the destination more quickly by following a zig-zag route on a series of broad reaches. Negotiating obstructions or a channel may also require a change of direction with respect to the wind, necessitating changing of tack with the wind on the opposite side of the craft, from before. Changing tack is called ''tacking'' when the wind crosses over the bow of the craft as it turns and ''jibing'' (or ''gybing'') if the wind passes over the stern.


Upwind

A sailing craft can sail on a course anywhere outside of its no-go zone. If the next waypoint or destination is within the arc defined by the no-go zone from the craft's current position, then it must perform a series of tacking maneuvers to get there on a dog-legged route, called ''beating to windward''. The progress along that route is called the ''course made good''; the speed between the starting and ending points of the route is called the ''speed made good'' and is calculated by the distance between the two points, divided by the travel time. The limiting line to the waypoint that allows the sailing vessel to leave it to leeward is called the ''layline''. Whereas some
Bermuda-rigged A Bermuda rig, Bermudian rig, or Marconi rig is a configuration of Mast (sailing), mast and rigging for a type of sailboat and is the typical configuration for most modern sailboats. This configuration was developed in Bermuda in the 17th century; ...
sailing yachts can sail as close as 30° to the wind, most 20th-Century square riggers are limited to 60° off the wind.
Fore-and-aft rig A fore-and-aft rig is a sailing Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' (sailing ship, sailboat, Windsurfing, windsurfer, or Kitesurfing, kitesurfer), on ''ice'' ( ...
s are designed to operate with the wind on either side, whereas
square rig Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square In Euclidean geometry, a square is a regular The term regular can mean norm ...
s and
kite A kite is a tether A tether is a cord, fixture, or flexible attachment that characteristically anchors something movable to something fixed; it also maybe used to connect two movable objects, such as an item being towing, towed by its tow. ...

kite
s are designed to have the wind come from one side of the sail only. Because the lateral wind forces are highest on a sailing vessel, close-hauled and beating to windward, the resisting water forces around the vessel's keel, centerboard, rudder and other foils is also highest to mitigate
leeway Leeway is the amount of drift motion to leeward Image:Upwind downwind example.png, 400px, Example image showing definitions of windward (upwind) and leeward (downwind) Windward () is the direction upwind from the point of reference, alternativ ...
—the vessel sliding to leeward of its course. Ice boats and land yachts minimize lateral motion with sidewise resistance from their blades or wheels.


=Changing tack by tacking

= ''Tacking'' or ''coming about'' is a maneuver by which a sailing craft turns its
bow Bow often refers to: * Bow and arrow The bow and arrow is a ranged weapon A ranged weapon is any weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict physical damage or harm. Weapons ar ...
into and through the wind (called the "eye of the wind") so that the apparent wind changes from one side to the other, allowing progress on the opposite tack. The type of sailing rig dictates the procedures and constraints on achieving a tacking maneuver. Fore-and-aft rigs allow their sails to hang limp as they tack; square rigs must present the full frontal area of the sail to the wind, when changing from side to side; and
windsurfer Windsurfing is a surface water sport that is a combination of surfing and sailing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the surf culture of California. Windsurfing had gained a following ...

windsurfer
s have flexibly pivoting and fully rotating masts that get flipped from side to side. File:Wende (Segeln).png, Tacking from the port tack (bottom) to the starboard (top) tack File:Tacking Intervals.svg, Beating to windward on short (P1), medium (P2), and long (P3) tacks


Downwind

A sailing craft can travel directly downwind only at a speed that is less than the wind speed. However, a variety of sailing craft can achieve a higher downwind velocity made good by traveling on a series of broad reaches, punctuated by jibes in between. This is true of ice boats and sand yachts. On the water it was explored by sailing vessels, starting in 1975, and now extends to high-performance skiffs, catamarans and foiling sailboats. Navigating a channel or a downwind course among obstructions may necessitate changes in direction that require a change of tack, accomplished with a jibe.


=Changing tack by jibing

= ''Jibing'' or ''gybing'' is a sailing maneuver by which a sailing craft turns its
stern The stern is the back or aft Aft :''For the acronym, see AFT (disambiguation).'' Aft, in naval A navy, naval force, or maritime force is the branch of a Nation's armed forces A military, also known collectively as armed forces, ...

stern
past the eye of the wind so that the apparent wind changes from one side to the other, allowing progress on the opposite tack. This maneuver can be done on smaller boats by pulling the tiller towards yourself (the opposite side of the sail). As with tacking, the type of sailing rig dictates the procedures and constraints for jibing. Fore-and-aft sails with booms, gaffs or sprits are unstable when the free end points into the eye of the wind and must be controlled to avoid a violent change to the other side; square rigs as they present the full area of the sail to the wind from the rear experience little change of operation from one tack to the other; and
windsurfer Windsurfing is a surface water sport that is a combination of surfing and sailing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the surf culture of California. Windsurfing had gained a following ...

windsurfer
s again have flexibly pivoting and fully rotating masts that get flipped from side to side.


Wind and currents

Winds and oceanic currents are both the result of the sun powering their respective fluid media. Wind powers the sailing craft and the ocean bears the craft on its course, as currents may alter the course of a sailing vessel on the ocean or a river. *''Wind'' – On a global scale, vessels making long voyages must take
atmospheric circulation Atmospheric circulation is the large-scale movement of air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of th ...

atmospheric circulation
into account, which causes zones of
westerlies The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend tow ...
,
easterlies The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere The Northern Hemisphere is the half of E ...
,
trade wind The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere The Northern Hemisphere is the half of Ear ...
s and high-pressure zones with light winds, sometimes called horse latitudes, in between. Sailors predict wind direction and strength with knowledge of high- and
low-pressure area In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mode ...
s, and the
weather front A weather front is a boundary separating air mass upright=1.25, Different air masses which affect North America as well as other continents, tend to be separated by frontal boundaries In meteorology Meteorology is a branch of the atmosphe ...
s that accompany them. Along coastal areas, sailors contend with diurnal changes in wind direction—flowing off the shore at night and onto the shore during the day. Local temporary wind shifts are called ''lifts'', when they improve the sailing craft's ability travel along its ''
rhumb line In navigation, a rhumb line, rhumb, () or loxodrome is an arc crossing all meridians of longitude at the same angle, that is, a path with constant bearing as measured relative to true north. Introduction The effect of following a rhumb ...
'' in the direction of the next waypoint. Unfavorable wind shifts are called ''headers''. *''Currents'' – On a global scale, vessels making long voyages must take major
ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind Wind is the natural movement of air or other gases relative to a planet's surface. Wind occurs on a range ...
circulation into account. Major oceanic currents, like the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current Boundary curren ...
in the Atlantic Ocean and the
Kuroshio Current The , also known as the Black or or the is a north-flowing, warm ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, ...
in the Pacific Ocean require planning for the effect that they will have on a transiting vessel's track. Likewise, tides affect a vessel's track, especially in areas with large tidal ranges, like the
Bay of Fundy The Bay of Fundy (french: Baie de Fundy) is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the US state of Maine. It has an extremely high tidal range. The name is likely a corruption of the F ...

Bay of Fundy
or along
Southeast Alaska Southeast Alaska, colloquially referred to as the Alaska Panhandle or Alaskan Panhandle, is the southeastern portion of the U.S. state In the United States The United States of America (U.S.A. or USA), commonly known as the United ...

Southeast Alaska
, or where the tide flows through
strait A strait is a naturally formed, narrowing, typically navigable waterway that connects two larger bodies of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly i ...

strait
s, like
Deception Pass Deception Pass is a strait A strait is a naturally formed, narrowing, typically navigable waterway that connects two larger bodies of water. The surface water generally flows at the same elevation on both sides and through the strait in eith ...

Deception Pass
in
Puget Sound Puget Sound () is a of the , an inlet of the , and part of the . It is located along the northwestern coast of the of . It is a complex system of interconnected marine waterways and basins, with one major and two minor connections to the ope ...
. Mariners use tide and current tables to inform their navigation. Before the advent of motors, it was advantageous for sailing vessels to enter or leave port or to pass through a strait with the tide.


Trimming

Trimming refers to adjusting the lines that control sails, including the sheets that control angle of the sails with respect to the wind, the halyards that raise and tighten the sail, and to adjusting the hull's resistance to heeling, yawing or progress through the water.


Sails

Square sails are controlled by two each of: sheets, braces, clewlines, and reef tackles, plus four buntlines, each of which may be controlled by a crew member as the sail is adjusted. Towards the end of the Age of Sail, steam-powered machinery reduced the number of crew required to trim sail. Adjustment of the angle of a fore-and-aft sail with respect to the apparent wind is controlled with a line, called a "sheet". On points of sail between close-hauled and a broad reach, the goal is typically to create flow along the sail to maximize power through lift. Streamers placed on the surface of the sail, called tell-tales, indicate whether that flow is smooth or turbulent. Smooth flow on both sides indicates proper trim. A jib and mainsail are typically configured to be adjusted to create a smooth
laminar flow In fluid dynamics In and , fluid dynamics is a subdiscipline of that describes the flow of s—s and es. It has several subdisciplines, including ' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in mo ...

laminar flow
, leading from one to the other in what is called the "slot effect". On downwind points of sail, power is achieved primarily with the wind pushing on the sail, as indicated by drooping tell-tales.
Spinnaker A spinnaker is a sail A sail is a tensile structure by Vladimir Shukhov (during construction), Nizhny Novgorod, 1895 in Kings Domain, Melbourne A tensile structure is a construction of elements carrying only tension (physics), tension ...

Spinnaker
s are light-weight, large-area, highly curved sails that are adapted to sailing off the wind. In addition to using the sheets to adjust the angle with respect to the apparent wind, other lines control the shape of the sail, notably the
outhaul An outhaul is a control line found on a sailboat sloop ged sloop Image:Sail plan sloop.svg, Gaff-rigged sloop with a Topsail#Gaff rig, gaff topsail A sloop is a sailboat with a single mast (sailing), mast typically having only one headsail in ...
,
halyard In sailing Sailing employs the wind—acting on sail A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboat sloop ged sloop Imag ...

halyard
,
boom vang A boom vang (US) or kicking strap (UK) is a line or piston system on a sailboat A sailboat or sailing boat is a boat A boat is a watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (fro ...
and
backstay A backstay is a piece of standing rigging File:Standing rigging--square-rigged sailing vessel--Detail.jpg, Standing rigging on a square-rigged vessel (illustrated left), which supports a mast comprising three steps: ''main'', ''top'', and ''topgall ...
. These control the curvature that is appropriate to the windspeed, the higher the wind, the flatter the sail. When the wind strength is greater than these adjustments can accommodate to prevent overpowering the sailing craft, then reducing sail area through
reefing Reefing is the means of reducing the area of a sail, usually by folding or rolling one edge of the canvas in on itself. The converse operation, removing the reef, is called "shaking it out." Reefing allows the carrying of partial sail in strong w ...
, substituting a smaller sail or by other means.


Reducing sail

Reducing sail on square-rigged ships could be accomplished by exposing less of each sail, by tying it off higher up with reefing points. Additionally, as winds get stronger, sails can be furled or removed from the spars, entirely until the vessel is surviving hurricane-force winds under "bare poles". On fore-and-aft rigged vessels, reducing sail may furling the jib and by reefing or partially lowering the mainsail, that is reducing the area of a sail without actually changing it for a smaller sail. This results both in a reduced sail area but also in a lower centre of effort from the sails, reducing the heeling moment and keeping the boat more upright. There are three common methods of reefing the mainsail: *Slab reefing, which involves lowering the sail by about one-quarter to one-third of its full length and tightening the lower part of the sail using an
outhaul An outhaul is a control line found on a sailboat sloop ged sloop Image:Sail plan sloop.svg, Gaff-rigged sloop with a Topsail#Gaff rig, gaff topsail A sloop is a sailboat with a single mast (sailing), mast typically having only one headsail in ...
or a pre-loaded reef line through a
cringle Image:Hals (Gennaker).jpg, A cringle at the corner of a sail. A cringle is an eye through which to pass a rope. In nautical settings, the word refers to a small hole anywhere along the edge or in the corner of a sail, rimmed with stranded cordage a ...
at the new
clew Sail components include the features that define a sail's shape and function, plus its constituent parts from which it is manufactured. A sail may be classified in a variety of ways, including by its orientation to the vessel (e.g. ''fore-and-af ...

clew
, and hook through a cringle at the new . *In-boom roller-reefing, with a horizontal foil inside the
boom Boom usually refers to an onomatopoeic word for the sound that an explosion makes. Boom may also refer to: Objects * Boom (containment), a temporary floating barrier used to contain an oil spill * Boom (navigational barrier), an obstacle strung ac ...

boom
. This method allows for standard- or full-length horizontal battens. *In-mast (or on-mast) roller-reefing. This method rolls the sail up around a vertical foil either inside a slot in the mast, or affixed to the outside of the mast. It requires a mainsail with either no
battens A batten is most commonly a strip of solid material, historically wood Wood is a porous and fibrous structural tissue found in the Plant stem, stems and roots of trees and other woody plants. It is an organic materiala natural composit ...
, or newly developed vertical battens.


Hull

Hull trim has three aspects, each tied to an axis of rotation, they are controlling: * Heeling (roll about the longitudinal axis) * Helm force (rotation about the vertical axis) * Hull drag (rotation about the horizontal axis amidships) Each is a reaction to forces on sails and is achieved either by weight distribution or by management of the center of force of the underwater foils (keel, daggerboard, etc.), compared with the center of force on the sails.


Heeling

A sailing vessel's form stability (the resistance of hull shape to rolling) is the starting point for resisting heeling. Catamarans and iceboats have a wide stance that makes them resistant to heeling. Additional measures for trimming a sailing craft to control heeling include: * Ballast in the keel, which counteracts heeling as the boat rolls. * Shifting of weight, which might be crew on a trapeze or moveable ballast across the boat. * Reducing sail * Adjusting the depth of underwater foils to control their lateral resistance force and center of resistance


Helm force

The alignment of center of force of the sails with center of resistance of the hull and its appendices controls whether the craft will track straight with little steering input, or whether correction needs to be made to hold it away from turning into the wind (a weather helm) or turning away from the wind (a lee helm). A center of force behind the center of resistance causes a weather helm. The center of force ahead of the center of resistance causes a lee helm. When the two are closely aligned, the helm is neutral and requires little input to maintain course.


Hull drag

Fore-and-aft weight distribution changes the cross-section of a vessel in the water. Small sailing craft are sensitive to crew placement. They are usually designed to have the crew stationed midships to minimize hull drag in the water.


Other aspects of seamanship

Seamanship Seamanship is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ideas. There is no generally agreed definition of wha ...
encompasses all aspects of taking a sailing vessel in and out of port, navigating it to its destination, and securing it at anchor or alongside a dock. Important aspects of seamanship include employing a common language aboard a sailing craft and the management of lines that control the sails and rigging.


Nautical terms

Nautical terms for elements of a vessel:
starboard Port and starboard are nautical Seamanship is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ideas. There is n ...
(right-hand side), port or larboard (left-hand side), forward or fore (frontward), aft or abaft (rearward), bow (forward part of the hull), stern (aft part of the hull), beam (the widest part). Spars, supporting sails, include masts, booms, yards, gaffs and poles. Moveable lines that control sails or other equipment are known collectively as a vessel's
running rigging Running rigging is the rigging Bermuda rigged sloop at Convict Bay, Bermuda, circa 1879 Rigging comprises the system of ropes, cables and chains, which support a sailing ship or sail boat's masts—''standing rigging'', including Shroud (sa ...
. Lines that raise sails are called ''
halyard In sailing Sailing employs the wind—acting on sail A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboat sloop ged sloop Imag ...

halyard
s'' while those that strike them are called ''downhauls''. Lines that adjust (trim) the sails are called '' sheets''. These are often referred to using the name of the sail they control (such as ''main sheet'' or ''jib sheet''). '' Guys'' are used to control the ends of other
spars The United States Coast Guard (USCG) Women's Reserve, known as the SPARS, was the World War II women's branch of the USCG Reserve. It was established by the United States Congress and signed into law by President Franklin D. Roosevelt on 23 Novem ...
such as
spinnaker pole 200px, A spinnaker pole being used to set a conventional symmetric spinnaker A spinnaker pole is a spar (sailing), spar used in sailboats (both dinghys and yachts) to help support and control a variety of headsails, particularly the spinnaker. ...
s. Lines used to tie a boat up when alongside are called ''docklines'', ''docking cables'' or ''mooring warps''. A ''rode'' is what attaches an anchored boat to its
anchor An anchor is a device, normally made of metal, used to connect a Watercraft, vessel to the Seabed, bed of a body of water to prevent the craft from drifting due to Leeway, wind or Ocean current, current. The word derives from Latin ''ancora'' ...

anchor
.


Management of lines

The following knots are regarded as integral to handling ropes and lines, while sailing: *
Bowline The bowline ( or ) is an ancient and simple knot A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bend Bend or bends may refer t ...

Bowline
– forms a loop at the end of a rope or line * Cleat hitch – affixes a line to a Cleat (nautical), cleat * Clove hitch – two half hitches around a post or other object * Figure-eight knot, Figure-eight – a stopper knot * Half hitch − a basic overhand knot around a line or object * Reef knot − (or square knot) joins two rope ends of equal diameter * Rolling hitch – a friction hitch to affix a line to itself or another object * Sheet bend – joins to rope ends of unequal diameter Lines and halyards are typically coiled neatly for stowage and reuse.


Sail physics

The physics of sailing arises from a balance of forces between the wind powering the sailing craft as it passes over its sails and the resistance by the sailing craft against being blown off course, which is provided in the water by the
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...

keel
,
rudder A rudder is a primary control surface used to steer a ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep Sea lane, waterways, carrying goods or passengers, or in support of specialized missions, su ...

rudder
, Foil (fluid mechanics), underwater foils and other elements of the underbody of a sailboat, on ice by the runners of an
iceboat An iceboat (occasionally spelled ice boat or traditionally called an ice yacht) is a recreational or competition sailing craft supported on metal runners for traveling over ice. One of the runners is steerable. Originally, such craft were boats ...

iceboat
, or on land by the wheels of a Land sailing, sail-powered land vehicle. Forces on sails depend on wind speed and direction and the speed and direction of the craft. The speed of the craft at a given point of sail contributes to the "
apparent wind 325px, V = boat speed, H = head wind, W = true wind, A = apparent wind, α = pointing angle, β = angle of apparent wind Apparent wind is the wind experienced by a moving object. Definition of apparent wind The ''apparent wind'' is the wind exper ...
"—the wind speed and direction as measured on the moving craft. The apparent wind on the sail creates a total aerodynamic force, which may be resolved into Drag (physics), drag—the force component in the direction of the apparent wind—and Lift (force), lift—the force component normal (geometry), normal (90°) to the apparent wind. Depending on the alignment of the sail with the apparent wind (''angle of attack''), lift or drag may be the predominant propulsive component. Depending on the angle of attack of a set of sails with respect to the apparent wind, each sail is providing motive force to the sailing craft either from lift-dominant attached flow or drag-dominant separated flow. Additionally, sails may interact with one another to create forces that are different from the sum of the individual contributions of each sail, when used alone.


Apparent wind velocity

The term "velocity" refers both to speed and direction. As applied to wind, ''apparent wind velocity'' (VA) is the air velocity acting upon the leading edge of the most forward sail or as experienced by instrumentation or crew on a moving sailing craft. In nautical terminology, wind speeds are normally expressed in Knot (unit), knots and wind angles in degree (angle), degrees. All sailing craft reach a constant ''forward velocity'' (VB) for a given ''true wind velocity'' (VT) and ''point of sail''. The craft's point of sail affects its velocity for a given true wind velocity. Conventional sailing craft cannot derive power from the wind in a "no-go" zone that is approximately 40° to 50° away from the true wind, depending on the craft. Likewise, the directly downwind speed of all conventional sailing craft is limited to the true wind speed. As a sailboat sails further from the wind, the apparent wind becomes smaller and the lateral component becomes less; boat speed is highest on the beam reach. To act like an airfoil, the sail on a sailboat is sheeted further out as the course is further off the wind. As an iceboat sails further from the wind, the apparent wind increases slightly and the boat speed is highest on the broad reach. In order to act like an airfoil, the sail on an iceboat is sheeted in for all three points of sail.


Lift and drag on sails

''Lift'' on a sail, acting as an airfoil, occurs in a direction ''perpendicular'' to the incident airstream (the apparent wind velocity for the headsail) and is a result of pressure differences between the windward and leeward surfaces and depends on the angle of attack, sail shape, air density, and speed of the apparent wind. The lift force results from the average pressure on the windward surface of the sail being higher than the average pressure on the leeward side. These pressure differences arise in conjunction with the curved airflow. As air follows a curved path along the windward side of a sail, there is a pressure gradient perpendicular to the flow direction with higher pressure on the outside of the curve and lower pressure on the inside. To generate lift, a sail must present an "angle of attack" between the Chord (aeronautics), chord line of the sail and the apparent wind velocity. The angle of attack is a function of both the craft's point of sail and how the sail is adjusted with respect to the apparent wind. As the lift generated by a sail increases, so does lift-induced drag, which together with parasitic drag constitute total ''drag'', which acts in a direction ''parallel'' to the incident airstream. This occurs as the angle of attack increases with sail trim or change of course and causes the lift coefficient to increase up to the point of aerodynamic stall along with the lift-induced drag coefficient. At the onset of stall, lift is abruptly decreased, as is lift-induced drag. Sails with the apparent wind behind them (especially going downwind) operate in a stalled condition. Lift and drag are components of the total aerodynamic force on sail, which are resisted by forces in the water (for a boat) or on the traveled surface (for an iceboat or land sailing craft). Sails act in two basic modes; under the ''lift-predominant'' mode, the sail behaves in a manner analogous to a ''wing'' with airflow attached to both surfaces; under the ''drag-predominant'' mode, the sail acts in a manner analogous to a ''parachute'' with airflow in detached flow, eddying around the sail.


Lift predominance (wing mode)

Sails allow progress of a sailing craft to windward, thanks to their ability to generate lift (and the craft's ability to resist the lateral forces that result). Each sail configuration has a characteristic coefficient of lift and attendant coefficient of drag, which can be determined experimentally and calculated theoretically. Sailing craft orient their sails with a favorable angle of attack between the entry point of the sail and the apparent wind even as their course changes. The ability to generate lift is limited by sailing too close to the wind when no effective angle of attack is available to generate lift (causing luffing) and sailing sufficiently off the wind that the sail cannot be oriented at a favorable angle of attack to prevent the sail from Stall (fluid dynamics), stalling with flow separation.


Drag predominance (parachute mode)

When sailing craft are on a course where the angle between the sail and the apparent wind (the angle of attack) exceeds the point of maximum lift, separation of flow occurs. Drag increases and lift decreases with increasing angle of attack as the separation becomes progressively pronounced until the sail is perpendicular to the apparent wind, when lift becomes negligible and drag predominates. In addition to the sails used upwind, spinnakers provide area and curvature appropriate for sailing with separated flow on downwind points of sail, analogous to parachutes, which provide both lift and drag.
;Downwind sailing with a spinnaker
File:Sailboat on broad reach with spinnaker.jpg, Spinnaker set for a broad reach, generating both lift, with separated flow, and drag. File:Spinnaker trimmed for broad reach.jpg, Spinnaker cross-section trimmed for a broad reach showing transition from boundary layer to separated flow where vortex shedding commences. File:Amante Choate 48 photo D Ramey Logan.jpg, Symmetric spinnaker while running downwind, primarily generating drag. File:Symmetrical spinnaker with following apparent wind.jpg, Symmetric spinnaker cross-section with following apparent wind, showing vortex shedding.


Wind variation with height and time

Wind speed increases with height above the surface; at the same time, wind speed may vary over short periods of time as gusts. Wind shear affects sailing craft in motion by presenting a different wind speed and direction at different heights along the mast (sailing), mast. Wind shear occurs because of friction above a water surface slowing the flow of air. The ratio of wind at the surface to wind at a height above the surface varies by a power law with an exponent of 0.11-0.13 over the ocean. This means that a wind at 3 m above the water would be approximately at above the water. In hurricane-force winds with at the surface the speed at would be This suggests that sails that reach higher above the surface can be subject to stronger wind forces that move the centre of effort on them higher above the surface and increase the heeling moment. Additionally, apparent wind direction moves aft with height above water, which may necessitate a corresponding Sail twist, twist in the shape of the sail to achieve attached flow with height. Gusts may be predicted by the same value that serves as an exponent for wind shear, serving as a gust factor. So, one can expect gusts to be about 1.5 times stronger than the prevailing wind speed (a 10-knot wind might gust up to 15 knots). This, combined with changes in wind direction suggest the degree to which a sailing craft must adjust sail angle to wind gusts on a given course.


Hull physics

Waterborne sailing craft rely on the design of the hull and keel to provide minimal forward drag in opposition to the sails' propulsive power and maximum resistance to the sails' lateral forces. In modern sailboats, drag is minimized by control of the hull's shape (blunt or fine), appendages, and slipperiness. The keel or other underwater foils provide the lateral resistance to forces on the sails. Heeling increases both drag and the ability of the boat to track along its desired course. Wave generation for a displacement hull is another important limitation on boat speed.


Drag

Drag due to its form is described by a Hull (watercraft), prismatic coefficient, Cp = displaced volume of the vessel divided by waterline length times maximum displaced section area—the maximum value of Cp = 1.0 being for a constant displace cross section area, as would be found on a barge. For modern sailboats, values of 0.53 ≤ Cp ≤ 0.6 are likely because of the tapered shape of the submerged hull towards both ends. Reducing interior volume allows creating a finer hull with less drag. Because a keel or other underwater foil produces lift, it also produces drag, which increases as the boat heels. Wetted area of the hull affects total the amount of friction between the water and the hull's surface, creating another component of drag.


Lateral resistance

Sailboats use some sort of underwater foil to generate lift that maintains the forward direction of the boat under sail. Whereas sails operate at angles of attack between 10° to 90° incident to the wind, underwater foils operate at angles of attack between 0° to 10° incident to the water passing by. Neither their angle of attack nor surface is adjustable (except for moveable foils) and they are never intentionally stalled. Heeling the vessel away from perpendicular into the water significantly degrades the boat's ability to point into the wind.


Wave generation

For displacement hulls have are limited in speed at a level defined by the square root of the boat's water line, the boat's hull speed. The addition of more power from sails or other source does not allow the vessel to go faster, it merely generates a wake with higher waves. Planing and foiling sailboats transcend this limitation, whereby speed becomes a linear function of power. Sailing craft on ice runners or wheels encounter forward resistance that depends on friction with their respective bearing surfaces.


See also

*Dinghy racing *High-performance sailing *Land sailing *
Racing Rules of Sailing The Racing Rules of Sailing (often abbreviated to RRS) govern the conduct of yacht racing, windsurfing, kitesurfing, model boat racing, dinghy racing and virtually any other form of racing around a course with more than one vessel while powered ...
*Sailing at the Summer Olympics *Single-handed sailing


Notes


Bibliography

*"Transportation and Maps" i
Virtual Vault
an online exhibition of Canadian historical art at Library and Archives Canada * Rousmaniere, John, ''The Annapolis Book of Seamanship'', Simon & Schuster, 1999 * ''Chapman Book of Piloting'' (various contributors), Hearst Corporation, 1999 * Herreshoff, Halsey (consulting editor), ''The Sailor's Handbook'', Little Brown and Company, 1983 * Seidman, David, ''The Complete Sailor'', International Marine, 1995 *


Further reading

* {{authority control Sailing,