Editing Sailing (section)

==Navigation==
[[File:Points of sail--English.jpg|thumb|right|'''Points of sail''' (and ''predominant sail force component'' for a displacement sailboat).<br />A. Luffing (''no propulsive force'') — 0-30°<br />B. Close-hauled (''lift'')— 30–50°<br />C. Beam reach (''lift'')— 90°<br />D. Broad reach (''lift–drag'')— ~135°<br />E. Running (''drag'')— 180°<br />True wind ('''V<sub>T</sub>''') is the same everywhere in the diagram, whereas boat velocity ('''V<sub>B</sub>''') and apparent wind ('''V<sub>A</sub>''') vary with point of sail.]]

===Point of sail===
{{Further|Point of sail}}
A sailing craft's ability to derive power from the wind depends on the [[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,<ref name = Complete>
{{cite book
 | last = Cunliffe
 | first = Tom
 | title = The Complete Day Skipper: Skippering with Confidence Right From the Start
 | publisher = Bloomsbury Publishing
 | edition = 5
 | date = 2016
 | page = 46
 | url = https://books.google.com/books?id=9b-gCwAAQBAJ&pg=PA46
 | isbn = 978-1-4729-2418-6 }}</ref> where a sail is unable to mobilize power from the wind.<ref name = Kimball/> 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]]s and [[land yacht]]s, this transition occurs further off the wind than for [[sailboat]]s and [[sailing ship]]s.<ref name = Kimball/>

Wind direction for points of sail always refers to the ''true wind''—the wind felt by a stationary observer. The ''[[apparent wind]]''—the wind felt by an observer on a moving sailing craft—determines the [[Forces on sails|motive power]] for sailing craft.
{{center|
;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.
}}
<gallery mode="packed" heights="175">
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.
</gallery>

====Effect on apparent wind====
{{Further|Forces on sails#Effect of points of sail on forces}}
True wind velocity ('''V<sub>T</sub>''') [[Euclidean vector#Addition and subtraction|combines]] with the sailing craft's velocity ('''V<sub>B</sub>''') to give the ''apparent wind velocity'' ('''V<sub>A</sub>'''), 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. It diminishes towards zero for a craft sailing dead downwind.<ref name=Jobson/>
{{center|
;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.<br />Boat velocity (in black) generates an equal and opposite apparent wind component (not shown), which combines with the true wind to become apparent wind.
}}
<gallery mode="packed" heights="300px">
File:Forces on sails for three points of sail.jpg|'''Apparent wind and forces on a ''sailboat''.'''<br />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''.'''<br />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.<ref name = Kimball/>
</gallery>

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.<ref name = Kimball/> 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.<ref name=Jobson/>

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.<ref name=Marchaj1>
{{Citation
 | last = Marchaj
 | first = C. A. 
 | title = Sail Performance: Techniques to Maximize Sail Power
 | publisher = International Marine/Ragged Mountain Press
 | year = 2002
 | edition = 2
 | pages = 416
 | isbn = 978-0071413107 }}</ref>
On ice boats, lateral forces are countered by the lateral resistance of the blades on ice and their distance apart, which generally prevents heeling.<ref>
{{cite book
 |last = Bethwaite
 |first = Frank
 |title = High Performance Sailing
 |publisher = Adlard Coles Nautical
 |year = 2007
 |isbn = 978-0-7136-6704-2}}</ref>

===Course under sail===
[[File:Atmospheric circulation.svg|thumb|[[Atmospheric circulation]], showing wind direction at various latitudes]]
[[File:Occluded cyclone.svg|thumb|Wind circulation around an [[Weather front#Occluded front|occluded front]] in the Northern Hemisphere]]
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.<ref name = Offshore>
{{cite book
 | last1 = Howard
 | first1 = Jim
 | last2 = Doane
 | first2 =  Charles J.
 | title = Handbook of Offshore Cruising: The Dream and Reality of Modern Ocean Cruising
 | date = 2000
 | url = https://books.google.com/books?id=NB4uFQuUlnEC&pg=PA214
 | page = 214
 | publisher = Sheridan House
 | isbn = 9781574090932 }}</ref>

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.<ref name=Cunliffe>
{{cite book
 | last = Cunliffe
 | first = Tom
 | title = The Complete Day Skipper: Skippering with Confidence Right From the Start
 | publisher = Bloomsbury Publishing
 | edition = 5
 | date = 2016
 | page=46
 | url = https://books.google.com/books?id=9b-gCwAAQBAJ&pg=PA46
 | isbn = 978-1-4729-2418-6 }}</ref> 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 (sailing)|tacking maneuvers]] to get there on a zigzag route, called ''beating to windward''.<ref name=Cruising>
{{cite journal|last=Cunliffe|first=Tom|date=January 1988|title=The shortest route to windward|url=https://books.google.com/books?id=InheK-WGcAcC&pg=PA63|journal=Cruising World|volume=14|issue=1|pages=58–64|issn=0098-3519}}</ref> 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.<ref name=Jobson2>
{{cite book
 | last = Jobson
 | first = Gary
 | title = Sailing Fundamentals
 | publisher = Simon and Schuster
 | edition = Revised
 | date = 2008
 | pages = 224
 | url = https://books.google.com/books?id=mKTrrP3wA-cC
 | isbn = 978-1-4391-3678-2 }}</ref> The limiting line to the waypoint that allows the sailing vessel to leave it to leeward is called the ''layline''.<ref name=Positioning>
{{cite book
 | last1 = Walker
 | first1 = Stuart H.
 | last2 = Price
 | first2 = Thomas C.
 | title = Positioning: The Logic of Sailboat Racing
 | publisher = W. W. Norton & Company
 | date = 1991
 | page = 192
 | url = https://books.google.com/books?id=5RWPv7tBnDsC&pg=PA192
 | isbn = 978-0-393-03339-7 }}</ref> Whereas some [[Bermuda rig|Bermuda-rigged]] sailing yachts can sail as close as 30° to the wind,<ref name=Jobson2/> most 20th-Century square riggers are limited to 60° off the wind.<ref name=Findlay>
{{cite book|last=Findlay|first=Gordon D.|url=https://books.google.com/books?id=OzFWjOMvGs4C&pg=PA138|title=My Hand on the Tiller|date=2005|publisher=AuthorHouse|isbn=9781456793500|page=138}}</ref> [[Fore-and-aft rig]]s are designed to operate with the wind on either side, whereas [[square rig]]s and [[kite]]s are designed to have the wind come from one side of the sail only.

Because the lateral wind forces are highest when sailing close-hauled, the resisting water forces around the vessel's keel, centerboard, rudder and other foils must also be highest in order to limit sideways motion or [[leeway]]. Ice boats and land yachts minimize lateral motion with resistance from their blades or wheels.<ref name=Fabio>{{cite book
 | last = Fossati
 | first = Fabio
 | title = Aero-hydrodynamics and the Performance of Sailing Yachts: The Science Behind Sailing Yachts and Their Design
 | publisher = Adlard Coles Nautical
 | date = 1 November 2009
| pages = 352
 | isbn = 978-1408113387 }}</ref>

=====Changing tack by tacking=====
{{Further|Tacking (sailing)#For various sailing craft}}
[[File:Canada and Vencedor – 1896.jpg|thumb|Two sailing yachts on opposite tacks]]
''Tacking'' or ''coming about'' is a maneuver by which a sailing craft turns its [[bow (ship)|bow]] into and through the wind (referred to as "the eye of the wind"<ref>{{Cite book |last=Ell |first=Sarah |url=https://books.google.com/books?id=DgxobVjcJSgC&dq=sailingl+%22eye+of+the+wind%22&pg=PA49 |title=Dinghy Sailing |date=2002 |publisher=Stackpole Books |isbn=978-0-8117-2474-6 |pages=49 |language=en}}</ref>) so that the apparent wind changes from one side to the other, allowing progress on the opposite tack.<ref name=Keegan>{{cite book |last=Keegan |first=John |author-link=John Keegan |title=The Price of Admiralty |publisher=Viking |date=1989 |location=New York |page=[https://archive.org/details/priceofadmiralty00keeg/page/281 281] |isbn=978-0-670-81416-9 |url=https://archive.org/details/priceofadmiralty00keeg/page/281 }}</ref> 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]]s have flexibly pivoting and fully rotating masts that get flipped from side to side.
<gallery mode="packed" heights="250px">
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
</gallery>

====Downwind====
[[File:18foot skiff Kiel2008.jpg|thumb|[[18ft Skiff]], flying a sprit-mounted asymmetrical spinnaker on a broad reach]]
A sailing craft can travel directly downwind only at a speed that is less than the wind speed. However,  some sailing craft such as [[iceboat]]s, [[land yacht|sand yachts]], and some [[High-performance sailing|high-performance sailboats]] can achieve a higher downwind [[velocity made good]] by traveling on a series of broad reaches, punctuated by jibes in between. It was explored by sailing vessels starting in 1975 and now extends to high-performance skiffs, catamarans and foiling sailboats.<ref name=Bethwaite>{{cite book|last =Bethwaite|first=Frank|title=High Performance Sailing|publisher=[[Adlard Coles]] Nautical|year=2007|isbn = 978-0-7136-6704-2|url=https://books.google.com/books?id=WTRLAAAAQBAJ}}</ref>

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=====
{{Further|Jibe#For various sailing craft}}
''Jibing'' or ''gybing'' is a sailing maneuver by which a sailing craft turns its [[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).<ref name=Keegan/> 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]]s again have flexibly pivoting and fully rotating masts that get flipped from side to side.

=== Wind and currents ===
[[File:Corrientes-oceanicas.png|thumb|The [[ocean current]]s]]
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]] into account, which causes zones of [[westerlies]], [[easterlies]], [[trade wind]]s and high-pressure zones with light winds, sometimes called [[horse latitude]]s, in between.<ref name="The Climate System: General Circulation and Climate Zones">{{cite web|author=Yochanan Kushnir|date=2000|title=The Climate System: General Circulation and Climate Zones|url=http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/index.html|access-date=13 March 2012|archive-date=22 August 2004|archive-url=https://web.archive.org/web/20040822022845/http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/index.html|url-status=dead}}</ref> Sailors predict wind direction and strength with knowledge of [[High-pressure area|high-]] and [[low-pressure area]]s, and the [[weather front]]s that accompany them. Along coastal areas, sailors contend with [[Diurnal temperature variation|diurnal change]]s in wind direction—flowing off the shore at night and onto the shore during the day.<ref name=Meteorology>
{{cite book|last1=Ahrens|first1=C. Donald|title=Meteorology Today|last2=Henson|first2=Robert|date=1 January 2015|publisher=Cengage Learning|isbn=9781305480629|edition=11|pages=656}}</ref> Local temporary wind shifts are called ''lifts'', when they improve the sailing craft's ability travel along its ''[[rhumb line]]'' in the direction of the next waypoint. Unfavorable wind shifts are called ''headers''.<ref name=Royce>
{{cite book|last=Royce|first=Patrick M.|url=https://books.google.com/books?id=mtqgsWaWciMC&pg=PA97|title=Royce's Sailing Illustrated|date=2015|publisher=ProStar Publications|isbn=978-0-911284-07-2|edition=11|volume=2|page=}}</ref>{{rp|97}}
*''Currents'' – On a global scale, vessels making long voyages must take major [[ocean current]] circulation into account.<ref name=NNOAACurrents>
{{cite web|last=National Ocean Service|date=25 March 2008|title=Surface Ocean Currents|url=http://oceanservice.noaa.gov/education/kits/currents/05currents1.html|website=noaa.gov|publisher=National Oceanic and Atmospheric Administration}}</ref> Major oceanic currents, like the [[Gulf Stream]] in the Atlantic Ocean and the [[Kuroshio Current]] 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,<ref name=Cruising/> like the [[Bay of Fundy]] or along [[Southeast Alaska]], or where the tide flows through [[strait]]s, like [[Deception Pass]] in [[Puget Sound]].<ref>{{cite web|date=December 2012|title=2.5 Tides and Currents|url=http://www.ecy.wa.gov/programs/spills/preparedness/GRP/NorthCentralPugetSound/NCPS-AllChapters.pdf|access-date=23 March 2016|work=North Central Puget Sound Geographic Response Plan|publisher=Washington Department of Ecology|pages=2–4}}</ref> Mariners use [[Tide table|tide and current tables]] to inform their navigation.<ref name = Offshore/> 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.<ref name=Findlay/>