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High-performance sailing is achieved with low forward surface resistance—encountered by catamarans, sailing hydrofoils, iceboats or land sailing craft—as the sailing craft obtains motive power with its sails or aerofoils at speeds that are often faster than the wind on both upwind and downwind points of sail. Faster-than-the-wind sailing means that the apparent wind angle experienced on the moving craft is always ahead of the sail.^[1] This has generated a new concept of sailing, called "apparent wind sailing", which entails a new skill set for its practitioners, including tacking on downwind points of sail.^[2]

History

Frank Bethwaite offers the following chronology of key advances in sailing technology that provided the essential elements of high-performance sailing:^[2]

1900s: Moveable ballast and planing hulls were emerging.
1960s: Flexible masts, sail-shaping controls, and knowledge of exploiting wind shifts in racing were developed.
1970s: Powerful rigs, including wingsails, offset by the crew trapezing from racks or wings allowed sailing faster than the wind and downwind tacking.

High-performance sailing craft

High-performance watercraft that can exceed the speed of the true wind include sailing catamarans and foiling sailing craft. Ice boats and land-sailing craft are often able to do so. There are also wind-powered vehicles that can travel faster than the wind, such as the rotor-powered Blackbird, which are outside the scope of this article.

Skiffs

Starting ca. 1975, 18ft Skiffs were sailing downwind faster than the speed of the wind. This meant that they had to tack, rather than jibe to change tacks.^[3] Other skiffs that can sail faster than the wind include the 29er, and 49er, both designed by Julian Bethwaite.^[4]

Multihulls

In 2013, a new class of catamaran was announced for the America's Cup which can achieve well in excess of double the speed of the wind.^[5] The catamarans used for the 2013 America's Cup were expected to sail upwind at 1.2 times the speed of the true wind, and downwind at 1.6 times the speed of the true wind.^[6]^[7]^[8] They proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0.^[9]

The Extreme 40 catamaran can sail at 35 knots (65 km/h; 40 mph) in 20–25-knot (37–46 km/h; 23–29 mph) winds.^[10] The high-performance International C-Class Catamaran can sail at twice the speed of the wind.^[11]

Hydrofoils

There are many varieties of sailing hydrofoils. Monohull examples include the International Moth, Laser, and AC75. America's Cup catamarans have used hydrofoils since 2013.^[12] Other foiling catamarans include A-Class,^[13] C-Class,^[14] Nacra 17, Nacra F20,^[15] and GC32.^[16]

In 2009, hydrofoil trimaran, Hydroptère, set the world speed sailing record on water at 50.17 knots (92.9 km/h), sailing at about 1.7 times the speed of the wind.^[17]^[18] In late 2012, Vestas Sailrocket 2 achieved a new outright world speed record of 65.45 knots (121.2 km/h) on water, at around 2.5 times the speed of the wind.^[19]

Iceboats

Iceboats on the Hudson River of New York in the second half of the 19th century were as long as 69 feet (21 m) and sailed as fast as 107 miles per hour (172 km/h), a record exceeding any other conveyance in 1885, set by the Icicle. Iceboats designs dating from the mid 20th century onwards typically consist of a triangular or cross-shaped frame, supported by three skate blades called "runners", with the steering runner in front. Runners are made of iron or steel with sharpened edges, which hold onto the ice, preventing slippage sideways from the lateral force of the wind in the sails, as they develop propulsive lift. Given their low forward resistance, iceboats can typically sail at five to six times the speed of the wind.^[3] Classic iceboats and Skeeters have reached speeds of 100–150 miles per hour (160–240 km/h). Record speeds are for a Skeeter: Das Boot, 155.9 miles per hour (250.9 km/h)^[20] and for a classic iceboat: Debutaunte, 143 miles per hour (230 km/h).^[21]^[22]

Land-sailing craft

By sailing downwind at 135° off the wind, a land-sailing craft can sail much faster than the wind.^[23] The velocity made good downwind is often over twice as fast compared to the same craft sailing directly downwind.^[23] In 2009, the world land speed record for a wind-powered vehicle was set by the sailing craft, Greenbird, sailing at about three times the speed of the wind^[24] with a recorded top speed of 202.9 kilometres per hour (126.1 mph).^[25]

Other high-performance sailing craft
DN class ice boat
Land-sailing craft

Apparent wind sailing

Whereas iceboats have been able to exceed the speed of the wind, both upwind and downwind for a century, this capability only became routine with the evolution of 18ft Skiffs in the third quarter of the 20th century when their speed tripled from that of the 1950s. Craft that sail faster than the speed of the wind, downwind as well as upwind, are capable of tacking downwind because the apparent wind is always ahead of the mast. This led to the concept of "apparent wind sailing".^[3]

Apparent wind

Apparent wind is the wind velocity (direction and speed), V_A, measured aboard a moving sailing craft; it is the net effect (vector sum) of the boat wind, V_B—the air flow over the craft induced by its speed over the earth (equal to in magnitude, but opposite in direction to the craft's speed)—and the true wind, V_T. The apparent wind measured aboard a craft under power, traveling in calm conditions, V_T = 0 knots, would come from directly ahead and at a speed that is the same as the boat speed over the bottom (V_A = V_B + 0 = V_B). If the craft travels at V_B = 10 knots with a tailwind of V_T = -5 knots, it experiences an apparent wind of V_A = 5 knots directly on the bow (V_A = V_B + V_T = 10 − 5). The apparent wind experienced by a stationary craft is the true wind speed. If a craft proceeds at 90° to a true wind of V_T = 10 knots, itself traveling at a speed inducing V_B = 10 knots, then the apparent wind angle would be 45° off the bow and the apparent wind speed would be about 14 knots, calculated as: square root [(V_B )² + (V_T )²] = square root [10² + 10²] = 14.14. As the craft becomes faster than the true wind, the apparent wind is always ahead of the sail.^[26]

When drag angle of the hull is negligible, the formulas for calculating V_A and β (the apparent wind angle) are:^[27]

V_A = square root {[V_T cos (90° – true wind angle)]² + [V_T sin (90° – true wind angle) + V_B]²}
β = 90° – arctan {[V_T sin (90° – true wind angle) + V_B] / [V_T cos (90° – true wind angle)]}

Sail power

A sail generates lift with a forward propulsive component and a sideways component, based on an optimum angle of attack that is constrained by the apparent wind, V_A, being forward of and approximately aligned with the sail.^[28]^[29]

Decomposition of wind force acting on a sail, generating lift.
(F_T = Total aerodynamic force, L = Lift
D =Drag, α = angle of attack)
Conversion of lift into propulsion.
(F_R = Propulsive force, F_LAT = Sideways force)

Beta theorem

β is the apparent wind angle from course over the water.^[26]

Garrett introduces the beta theorem (or course theorem) as a way to understand how apparent wind angle results from the interplay between the driving force from the wind and the resisting force from the water (or hard surface), the result of the net effect of two counteracting foils, the sail in the air and the keel in the water. When one resolves the ratio of lift to drag for each in its medium, the resulting motion of the sailing craft resolves to an angle, beta (β), between the apparent wind and the course over the water. The hull (below the water) and the sailing rig (above the water) each have drag angle with respect to the medium flowing past them (water or air), they are λ and α_m in the accompanying diagram. The sum of those two drag angles are equal to β, the angle between the apparent wind and the course sailed (β = λ + α_m). This theorem applies for every point of sail. A small β denotes high efficiency and a potential for high speed.^[26] As forward velocity increases, β becomes smaller; on sailing craft with effective underwater foils the drag angle of the hull, λ, becomes smaller with increased speed, it becomes negligible with hydrofoiling craft, and essentially nonexistent for ice boats and land sailing craft.^[30]

Apparent-wind-angle limit

Given an ideal circumstance of a frictionless surface and an airfoil that can develop power, there is no theoretical limit to how fast a sailing craft can travel off the wind as the apparent wind angle becomes ever smaller. In reality, both sail efficiency and friction provide an upper limit. Speed is determined by the ratio of power developed by the sail over power lost through various forms of drag (e.g. surface drag and aerodynamic drag). Ideally a smaller sail is better, as speeds increase. Unfortunately, a small sail diminishes the ability for a craft—even an iceboat—to accelerate to speeds faster than the wind. The principal limit to speed in high-performance sailing craft is form drag. Efforts to overcome this limit is evident in the streamlined hulls of high-performance iceboats and the improvements in drag reduction on planing dinghies. A fast iceboat can achieve an apparent wind of 7.5° and a speed of six times the true wind speed on a course that is 135° off the wind. Bethwaite suggests this might be a practical limit for a craft powered by sails.^[3]

Points of sail

The points of sail at which high-performance sailing craft can achieve highest speeds and achieve the best speed made good^[31] over a course span between a beam reach (90° to the true wind) and a broad reach (about 135° away from the true wind). According to Bethwaite, having made comparative measurements in a true wind of 15 knots (28 km/h; 17 mph), a displacement Soling can achieve speeds slightly higher than the true wind and sail 30° off the apparent wind, whereas a planing 18ft Skiff achieves speeds of almost 30 knots (56 km/h; 35 mph) at an apparent wind of 20° and an iceboat can achieve 67 knots (124 km/h; 77 mph) at an apparent wind of 8°.^[2]

Under apparent wind sailing, the objective is to keep the apparent wind as far forward as practical for the course sailed in order to attain the fastest course made good^[31] to the objective. This requires a craft that can exceed the true windspeed, both upwind and downwind; this allows the apparent wind to remain well ahead of the sail on the courses sailed, the fastest of which are reaches. To be avoided is heading too far downwind, where the apparent wind moves behind the sail and the speed drops below the true windspeed as the course trends from a broad reach to running square (dead down wind).^[3]

Upwind

Depending on the craft sailed, the course made good into the wind may trend away from its closest point into the wind in order to allow the craft to sail at optimum speed.^[3] Bethwaite explains that high-speed sailing demands independent action of both the tiller and the mainsheet, whereby the person at the helm avoids responding to gusts and, instead, eased the mainsheet as needed, thus increasing the boat's velocity made good over the previous technique of pointing the craft more into the wind.^[4]

Off the wind

According to Bethwaite, sailing off the true wind at speeds faster than the wind (with the apparent wind forward of the sail) demands a different reaction to gusts than previously employed. Whereas a traditional sailor might reflexively steer into the apparent wind in a gust, the correct response while sailing off wind, faster than the true wind speed is to veer away from the gust, heading more downwind. This has the doubly beneficial effect of relieving the heeling force of the gust and allowing the craft to sail yet faster off the wind.^[4]

References

^ Jobson, Gary (1990). Championship Tactics: How Anyone Can Sail Faster, Smarter, and Win Races. New York: St. Martin's Press. pp. 323. ISBN 0-312-04278-7.
^ ^a ^b ^c Bethwaite, Frank (2007). High Performance Sailing. Adlard Coles Nautical. ISBN 978-0-7136-6704-2.
^ ^a ^b ^c ^d ^e ^f ^g Bethwaite, Frank (2008). Higher performance sailing. London: Adlard Coles Nautical. ISBN 978-1-4729-0131-6. OCLC 854680844.
^ ^a ^b ^c Bethwaite, Frank (12 May 2013). Fast Handling Technique. New York: A&C Black. pp. 5–6. ISBN 978-1-4081-7860-7.
^ How yachts go faster than the wind Gray, R. The Telegraph 26 September 2013
^ "AC34 Multihull Class Rule Concept Document" (PDF). 34th America's Cup. Retrieved 14 September 2010.
^ "New high performance yachts for 34th America's Cup" (PDF). 34th America's Cup. 2 July 2010. Retrieved 14 September 2010.
^ The monohull concept for the 34th America's Cup called for a design that would achieve 1.0 times true wind speed upwind and 1.4 times downwind, see "AC34 Monohull Class Rule Concept Document" (PDF). 34th America's Cup. Retrieved 14 September 2010.
^ "Emirates Team New Zealand gets leg up on ORACLE TEAM USA". 2012-13 America's Cup Event Authority. 7 September 2013. Archived from the original on 21 September 2013. Retrieved 8 September 2013.
^ "About eXtreme 40". eXtreme40. Archived from the original on 12 August 2010. Retrieved 25 August 2010.
^ "The Winged World of C Cats". Sail Magazine. Archived from the original on 14 March 2010. Retrieved 25 August 2010.
^ Clarey, Christopher (9 June 2016). "Sailing Into America's Cup History in Chicago". The New York Times. ISSN 0362-4331. Retrieved 3 August 2020.
^ Griffits, Bob (11 February 2014). "Worlds @Takapuna: Day 1, Report by Bob Griffits | International A-Division Catamaran Association". www.a-cat.org. Retrieved 2 August 2020.
^ Block, Alan (22 September 2013). "Foiling 'Little Cup' Cats set for prestigious C-Class Championship Trophy". www.yachtsandyachting.com. Retrieved 2 August 2020.
^ McArthur, Bruce (2020). "Nacra 20 sailboat". sailboatdata.com. Archived from the original on 27 July 2020. Retrieved 27 July 2020.
^ "GC32s to replace Extreme 40s". www.extremesailingseries.com. Retrieved 2 August 2020.
^ The 500-meter record was 51.36 knots (95.12 km/h; 59.10 mph), achieved in 30-knot (56 km/h; 35 mph) winds by Hydroptère, a hydrofoil trimaran, see "Hydroptère World Records". World Sailing Speed Record Council. 23 September 2009. Retrieved 25 August 2010.
^ "Official web site of l'Hydroptère". Archived from the original on 7 October 1999. Retrieved 25 August 2010.{{cite web}}: CS1 maint: unfit URL (link)
^ "500 Metre Records". World Sailing Speed Record Council.
^ Spectre, Peter H. (2006). A mariner's book of days, 2007. Dobbs Ferry, NY: Sheridan House. ISBN 1-57409-226-X. OCLC 173009383.
^ Dill, Bob (March 2003), "Sailing Yacht Design for Maximum Speed", The 16th Chesapeake Sailing Yacht Symposium, Anapolis: SNAME, archived from the original (PDF) on 19 September 2020, retrieved 2 August 2020
^ Smith, Doug (January–February 2004). Sailing on slivers of steel. Boy Scouts of America, Inc. pp. 18–21.
^ ^a ^b Bob Dill (13 July 2003). "Frequently Asked Questions". North American Land Sailing Association. Retrieved 25 August 2010.
^ The record was 126 mph (109 kn; 203 km/h) with winds of 30–50 mph (48–80 km/h), see Bob Dill (5 April 2009). "Measurement report for Speed Record Attempt Made by Richard Jenkins in the Yacht Greenbird on March 26, 2008". North American Land Sailing Association. Retrieved 25 August 2010.
^ "Wind-powered car breaks record". BBC New, UK. 27 March 2009. Retrieved 28 January 2017.
^ ^a ^b ^c Garrett, Ross (1996). The Symmetry of Sailing: The Physics of Sailing for Yachtsmen. Sheridan House, Inc. p. 268. ISBN 978-1-57409-000-0.
^ McEwen, Thomas (2006). Boater's Pocket Reference: Your Comprehensive Resource for Boats and Boating. Anchor Cove Publishing, Inc. p. 182. ISBN 978-0-9774052-0-6.
^ Batchelor, G.K. (1967), An Introduction to Fluid Dynamics, Cambridge University Press, pp. 14–15, ISBN 978-0-521-66396-0
^ Klaus Weltner A comparison of explanations of the aerodynamic lifting force Am. J. Phys. 55(1), January 1987 pg 52
^ Kimball, John (22 December 2009). Physics of Sailing. CRC Press. ISBN 978-1-4200-7377-5.
^ ^a ^b Walker, George K. (28 October 2011). Definitions for the Law of the Sea: Terms Not Defined by the 1982 Convention. Martinus Nijhoff Publishers. pp. 158, 303. ISBN 978-90-04-21160-5.

External links

[Jobson-1] Jobson, Gary (1990). Championship Tactics: How Anyone Can Sail Faster, Smarter, and Win Races. New York: St. Martin's Press. pp. 323. ISBN 0-312-04278-7.

[Bethwaite-2] Bethwaite, Frank (2007). High Performance Sailing. Adlard Coles Nautical. ISBN 978-0-7136-6704-2.

[:0-3] ^ ^a ^b ^c ^d ^e ^f ^g Bethwaite, Frank (2008). Higher performance sailing. London: Adlard Coles Nautical. ISBN 978-1-4729-0131-6. OCLC 854680844.

[:2-4] Bethwaite, Frank (12 May 2013). Fast Handling Technique. New York: A&C Black. pp. 5–6. ISBN 978-1-4081-7860-7.

[5] How yachts go faster than the wind Gray, R. The Telegraph 26 September 2013

[6] "AC34 Multihull Class Rule Concept Document" (PDF). 34th America's Cup. Retrieved 14 September 2010.

[7] "New high performance yachts for 34th America's Cup" (PDF). 34th America's Cup. 2 July 2010. Retrieved 14 September 2010.

[8] The monohull concept for the 34th America's Cup called for a design that would achieve 1.0 times true wind speed upwind and 1.4 times downwind, see "AC34 Monohull Class Rule Concept Document" (PDF). 34th America's Cup. Retrieved 14 September 2010.

[2013first2-9] "Emirates Team New Zealand gets leg up on ORACLE TEAM USA". 2012-13 America's Cup Event Authority. 7 September 2013. Archived from the original on 21 September 2013. Retrieved 8 September 2013.

[10] "About eXtreme 40". eXtreme40. Archived from the original on 12 August 2010. Retrieved 25 August 2010.

[11] "The Winged World of C Cats". Sail Magazine. Archived from the original on 14 March 2010. Retrieved 25 August 2010.

[12] Clarey, Christopher (9 June 2016). "Sailing Into America's Cup History in Chicago". The New York Times. ISSN 0362-4331. Retrieved 3 August 2020.

[13] Griffits, Bob (11 February 2014). "Worlds @Takapuna: Day 1, Report by Bob Griffits | International A-Division Catamaran Association". www.a-cat.org. Retrieved 2 August 2020.

[14] Block, Alan (22 September 2013). "Foiling 'Little Cup' Cats set for prestigious C-Class Championship Trophy". www.yachtsandyachting.com. Retrieved 2 August 2020.

[Data-15] McArthur, Bruce (2020). "Nacra 20 sailboat". sailboatdata.com. Archived from the original on 27 July 2020. Retrieved 27 July 2020.

[16] "GC32s to replace Extreme 40s". www.extremesailingseries.com. Retrieved 2 August 2020.

[17] The 500-meter record was 51.36 knots (95.12 km/h; 59.10 mph), achieved in 30-knot (56 km/h; 35 mph) winds by Hydroptère, a hydrofoil trimaran, see "Hydroptère World Records". World Sailing Speed Record Council. 23 September 2009. Retrieved 25 August 2010.

[18] "Official web site of l'Hydroptère". Archived from the original on 7 October 1999. Retrieved 25 August 2010.{{cite web}}: CS1 maint: unfit URL (link)

[19] "500 Metre Records". World Sailing Speed Record Council.

[:4-20] Spectre, Peter H. (2006). A mariner's book of days, 2007. Dobbs Ferry, NY: Sheridan House. ISBN 1-57409-226-X. OCLC 173009383.

[Boat_Speed-21] Dill, Bob (March 2003), "Sailing Yacht Design for Maximum Speed", The 16th Chesapeake Sailing Yacht Symposium, Anapolis: SNAME, archived from the original (PDF) on 19 September 2020, retrieved 2 August 2020

[22] Smith, Doug (January–February 2004). Sailing on slivers of steel. Boy Scouts of America, Inc. pp. 18–21.

[nalsa_faq3-23] Bob Dill (13 July 2003). "Frequently Asked Questions". North American Land Sailing Association. Retrieved 25 August 2010.

[nalsa_record-24] The record was 126 mph (109 kn; 203 km/h) with winds of 30–50 mph (48–80 km/h), see Bob Dill (5 April 2009). "Measurement report for Speed Record Attempt Made by Richard Jenkins in the Yacht Greenbird on March 26, 2008". North American Land Sailing Association. Retrieved 25 August 2010.

[25] "Wind-powered car breaks record". BBC New, UK. 27 March 2009. Retrieved 28 January 2017.

[Garrett-26] Garrett, Ross (1996). The Symmetry of Sailing: The Physics of Sailing for Yachtsmen. Sheridan House, Inc. p. 268. ISBN 978-1-57409-000-0.

[27] McEwen, Thomas (2006). Boater's Pocket Reference: Your Comprehensive Resource for Boats and Boating. Anchor Cove Publishing, Inc. p. 182. ISBN 978-0-9774052-0-6.

[28] Batchelor, G.K. (1967), An Introduction to Fluid Dynamics, Cambridge University Press, pp. 14–15, ISBN 978-0-521-66396-0

[29] Klaus Weltner A comparison of explanations of the aerodynamic lifting force Am. J. Phys. 55(1), January 1987 pg 52

[30] Kimball, John (22 December 2009). Physics of Sailing. CRC Press. ISBN 978-1-4200-7377-5.

[:1-31] Walker, George K. (28 October 2011). Definitions for the Law of the Sea: Terms Not Defined by the 1982 Convention. Martinus Nijhoff Publishers. pp. 158, 303. ISBN 978-90-04-21160-5.

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@@ Line 1: / Line 1: @@
+{{Short description|Optimizing sailboat speed}}
-'''THIS PAGE IS UNDER CONSTRUCTION'''
+{{Use dmy dates|date=March 2023}}
+{{Use Australian English|date=March 2023}}
+[[File:18foot skiff Kiel2008.jpg|thumb|300px|[[18ft Skiff]] in [[Kiel, Germany|Kiel Harbor]]]]
+'''High-performance sailing''' is achieved with low forward surface resistance—encountered by [[catamaran]]s, [[sailing hydrofoil]]s, [[iceboat]]s or [[land sailing]] craft—as the sailing craft obtains motive power with its sails or aerofoils at speeds that are often faster than the wind on both upwind and downwind points of sail. Faster-than-the-wind sailing means that the apparent wind angle experienced on the moving craft is always ahead of the sail.<ref name=Jobson>{{cite book | last = Jobson | first = Gary | title = Championship Tactics: How Anyone Can Sail Faster, Smarter, and Win Races | publisher = St. Martin's Press | location = New York | year = 1990 | isbn = 0-312-04278-7 | pages = [https://archive.org/details/championshiptact00jobs/page/323 323] | url = https://archive.org/details/championshiptact00jobs/page/323 }}</ref> This has generated a new concept of sailing, called "apparent wind sailing", which entails a new skill set for its practitioners, including tacking on downwind points of sail.<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&q=faster+than+the+wind}}</ref>
+== History ==
+[[Frank Bethwaite]] offers the following chronology of key advances in sailing technology that provided the essential elements of high-performance sailing:<ref name="Bethwaite" />
+* 1900s: Moveable ballast and planing hulls were emerging.
+* 1960s: Flexible masts, sail-shaping controls, and knowledge of exploiting wind shifts in racing were developed.
+* 1970s: Powerful rigs, including [[wingsail]]s, offset by the crew trapezing from racks or wings allowed sailing faster than the wind and downwind tacking.
+== High-performance sailing craft ==
-Devices that are powered by sails (such as [[sailboat|sailboats]] and [[iceboat|iceboats]] can sail faster than the wind.  Of course they cannot do that by using simple square [[sail|sails]] that are set perpendicular to the wind.  But they can do that by setting sails at an angle to the wind and by using the resistance of the surface on which they sail (for example the water or the ice) to maintain a course at some other angle to the wind.
+[[File:Oracle Team USA in the 2013 America's Cup.JPG|thumb|Oracle sailing [[hydrofoil]] catamaran with [[wingsail]] in the 2013 America's Cup]]High-performance watercraft that can exceed the speed of the true wind include sailing catamarans and foiling sailing craft. Ice boats and land-sailing craft are often able to do so. There are also [[wind-powered vehicle]]s that can travel faster than the wind, such as the rotor-powered [[Blackbird (land yacht)|''Blackbird'']], which are outside the scope of this article.
+=== Skiffs ===
-For example, a boat can sail a course that is perpendicular to the true wind.  As it accelerates, the wind as seen from the boat will increase and the wind will appear to shift forward<ref>''Forward'' means making a smaller angle relative to the bow than the angle that the true wind makes relative to the bow</ref>.  This is the same effect that causes rain to appear to fall at angle when seen from a moving car, and that causes your hand to be blown backwards when you stick it out of the window of a moving car.
+Starting ca. 1975, [[18ft Skiff]]s were sailing downwind faster than the speed of the wind. This meant that they had to tack, rather than jibe to change tacks.<ref name=":0">{{Cite book|last=Bethwaite|first=Frank|url=https://books.google.com/books?id=WTRLAAAAQBAJ&q=Higher+Performance+Sailing+-+Google+Books|title=Higher performance sailing|date=2008|publisher=Adlard Coles Nautical|isbn=978-1-4729-0131-6|location=London|oclc=854680844}}</ref> Other skiffs that can sail faster than the wind include the [[29er (dinghy)|29er]], and [[49er (dinghy)|49er]], both designed by [[Julian Bethwaite]].<ref name=":2" />
+=== Multihulls ===
-As the wind increases in speed and shifts forward (because of the acceleration of the boat), the sails have to be trimmed in order to maintain performance.  This causes the boat to further accelerate, thus causing a further increase in windspeed and a further forward windshift.
+In 2013, a new class of catamaran was announced for the America's Cup which can achieve well in excess of double the speed of the wind.<ref>[https://www.telegraph.co.uk/sport/othersports/sailing/10335496/Americas-Cup-how-the-yachts-go-faster-than-the-wind.html How yachts go faster than the wind Gray, R. ''The Telegraph'' 26 September 2013]</ref> The [[catamarans]] used for the [[2013 America's Cup]] were expected to sail upwind at 1.2 times the speed of the true wind, and downwind at 1.6 times the speed of the true wind.<ref>{{cite web | url = http://www.cupinfo.com/downloads/ac34-class-rule-multihull-concept.pdf | title = AC34 Multihull Class Rule Concept Document | publisher = 34th America's Cup | access-date = 2010-09-14}}</ref><ref>{{cite web | url = http://www.cupinfo.com/downloads/ggyc-press-ac34-rule-writing-070110.pdf| title = New high performance yachts for 34th America's Cup | publisher = 34th America's Cup | date = 2 July 2010 | access-date=2010-09-14}}</ref><ref>The monohull concept for the 34th America's Cup called for a design that would achieve 1.0 times true wind speed upwind and 1.4 times downwind, see {{cite web | url = http://www.cupinfo.com/downloads/ac34-class-rule-canting-monohull-concept.pdf | title = AC34 Monohull Class Rule Concept Document | publisher = 34th America's Cup | access-date=2010-09-14}}</ref> They proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0.<ref name=2013first2>{{cite web|url=http://www.americascup.com/en/news/3/news/18009/emirates-team-new-zealand-gets-leg-up-on-oracle-team-usa |title=Emirates Team New Zealand gets leg up on ORACLE TEAM USA |publisher=2012-13 America's Cup Event Authority |date=7 September 2013 |access-date=8 September 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130921055314/http://www.americascup.com/en/news/3/news/18009/emirates-team-new-zealand-gets-leg-up-on-oracle-team-usa |archive-date=21 September 2013 }}</ref>
+The [[Extreme 40]] catamaran can sail at {{convert|35|kn}} in {{convert|20|–|25|kn|adj=on}} winds.<ref>{{cite web | url = http://www.extreme40.org/extreme40.asp?pid=152 | title = About eXtreme 40 | publisher = eXtreme40 | access-date = 2010-08-25 | archive-url = https://web.archive.org/web/20100812115124/http://www.extreme40.org/extreme40.asp?pid=152 | archive-date = 2010-08-12 | url-status = dead }}</ref> The high-performance [[International C-Class Catamaran]] can sail at twice the speed of the wind.<ref>{{cite web|url=http://www.sailmagazine.com/cclasscats/ |publisher=Sail Magazine |title=The Winged World of C Cats |access-date=2010-08-25 |url-status=dead |archive-url=https://web.archive.org/web/20100314051043/http://www.sailmagazine.com/cclasscats/ |archive-date=March 14, 2010 }}</ref>
-Eventually, the sails cannot be trimmed any further and an equlibrium is reached.  Although the boat is sailing perpendicular to the true wind, its sails are set for a [[points_of_sail#close_hauled|close hauled]] course.
+=== Hydrofoils ===
-The actual speed of the boat in such a situation depends on the wind speed, how close to the wind it can sail, the strength of the wind , the resistance of the surface (water or ice), and [[leeway]] (downwind drift).  Normal yachts can sail at a about 45 degress off the apparent wind.  High performance racing yachts at about 35 degrees.<ref>[[Sailing]]</ref>  High-performance multihulls can sail at 20 degrees off the apparent wind.<ref>http://www.cupinfo.com/en/bmwo-multihull-san-diego-coutts-002.php</ref>  Iceboats can sail even closer to the apparent wind<ref>[[Iceboat]]</ref>.
+There are many varieties of [[sailing hydrofoil]]s. Monohull examples include the [[Moth (dinghy)|International Moth]], [[Laser (dinghy)|Laser]], and [[America's Cup 75 class|AC75]]. [[America's Cup]] catamarans have used hydrofoils since 2013.<ref>{{Cite news|last=Clarey|first=Christopher|date=2016-06-09|title=Sailing Into America's Cup History in Chicago|language=en-US|work=The New York Times|url=https://www.nytimes.com/2016/06/10/sports/sailing-into-americas-cup-history-in-chicago.html|access-date=2020-08-03|issn=0362-4331}}</ref> Other foiling catamarans include A-Class,<ref>{{Cite web|last=Griffits|first=Bob|date=February 11, 2014|title=Worlds @Takapuna: Day 1, Report by Bob Griffits {{!}} International A-Division Catamaran Association|url=https://www.a-cat.org/?q=node/359|access-date=2020-08-02|website=www.a-cat.org}}</ref> C-Class,<ref>{{Cite web|last=Block|first=Alan|date=22 September 2013|title=Foiling 'Little Cup' Cats set for prestigious C-Class Championship Trophy|url=https://www.yachtsandyachting.com/news/172395/Foiling-Little-Cup-Cats-set|access-date=2020-08-02|website=www.yachtsandyachting.com}}</ref> Nacra 17, Nacra F20,<ref name="Data">{{cite web|last=McArthur|first=Bruce|year=2020|title=Nacra 20 sailboat|url=https://sailboatdata.com/sailboat/nacra-20|url-status=live|archive-url=https://archive.today/20200727151914/https://sailboatdata.com/sailboat/nacra-20|archive-date=27 July 2020|access-date=27 July 2020|work=sailboatdata.com}}</ref> and GC32.<ref>{{Cite web|title=GC32s to replace Extreme 40s|url=https://www.extremesailingseries.com/news/view/gc32s-to-replace-extreme-40s-as-the-extreme-sailing-series-fast-tracks-to-a|access-date=2020-08-02|website=www.extremesailingseries.com|language=en}}</ref>
+In 2009, [[hydrofoil]] [[trimaran]], ''[[Hydroptère]]'', set the world [[speed sailing record]] on water at {{Convert|50.17|kn|km/h|1|abbr=}}, sailing at about 1.7 times the speed of the wind.<ref>The 500-meter record was {{convert|51.36|kn}}, achieved in {{convert|30|kn|adj=on}} winds by [[Hydroptère]], a [[hydrofoil]] [[trimaran]], see {{cite web | url=http://www.sailspeedrecords.com/index.php?option=com_content&view=article&id=104:wssr-newsletter-no-177-hydroptere-world-records-230909&catid=2:news&Itemid=5 | title = Hydroptère World Records | publisher = World Sailing Speed Record Council | date = September 23, 2009 | access-date = 2010-08-25}}</ref><ref>{{cite web | url=http://www.hydroptere.com/ | archive-url=https://web.archive.org/web/19991007144526/http://www.hydroptere.com/ | url-status=usurped | archive-date=7 October 1999 | title=Official web site of l'Hydroptère | access-date=2010-08-25}}</ref> In late 2012, ''[[Vestas Sailrocket]] 2'' achieved a new outright world speed record of {{Convert|65.45|kn|km/h|1|abbr=}} on water, at around 2.5 times the speed of the wind.<ref>{{cite web |url=http://www.sailspeedrecords.com/500-metre |title=500 Metre Records |website=World Sailing Speed Record Council}}</ref>
-If [[hull speed]] is not a limiting factor, and if the strength of the wind is sufficient to overcome the surface resistance, then the speed of the boat as a multiple of the wind speed will depend only on how close it can sail to the wind.  For example, assuming that surface resistance is neglible (as for an iceboat), if a boat sails at 90 degrees to the true wind, but at 45 degress to the apparent wind, then it must be sailing at the same speed as the true wind.  That is, if the wind speed is V, then the boat's speed is also V.  Elementary [[trigonometry]] can be used to show that, if a boat sails at 90 degrees to the true wind, but at alpha degress to the apparent wind, and the wind speed is V, then the boat's speed must be V*cotan(alpha).  The table below shows the values of this function, as a multiple of windspeed:
+=== Iceboats ===
-    alpha   multiple of windspeed
+Iceboats on the Hudson River of New York in the second half of the 19th century were as long as {{Convert|69|ft|m|abbr=}} and sailed as fast as {{Convert|107|mi/h|km/h|abbr=}}, a record exceeding any other conveyance in 1885, set by the ''[[Icicle (yacht)|Icicle]]''. Iceboats designs dating from the mid 20th century onwards typically consist of a triangular or cross-shaped frame, supported by three skate blades called "runners", with the steering runner in front. Runners are made of iron or steel with sharpened edges, which hold onto the ice, preventing slippage sideways from the lateral force of the wind in the sails, as they develop [[Forces on sails|propulsive lift]]. Given their low forward resistance, iceboats can typically sail at five to six times the speed of the wind.<ref name=":0" /> Classic iceboats and Skeeters have reached speeds of {{Convert|100-150|mph|km/h|abbr=}}. Record speeds are for a Skeeter: ''Das Boot'', {{Convert|155.9|mph|km/h|abbr=}}<ref name=":4">{{Cite book|last=Spectre|first=Peter H.|title=A mariner's book of days, 2007|date=2006|publisher=Sheridan House|isbn=1-57409-226-X|location=Dobbs Ferry, NY|oclc=173009383}}</ref> and for a classic iceboat: ''Debutaunte'', {{Convert|143|mph|km/h|abbr=}}.<ref name="Boat_Speed">{{Citation|last=Dill|first=Bob|title=The 16th Chesapeake Sailing Yacht Symposium|date=March 2003|url=http://www.sname.org/chesapeakesailingyachtsymposiumcsys/pastpapers/16thcsys|contribution=Sailing Yacht Design for Maximum Speed|contribution-url=http://static1.1.sqspcdn.com/enwiki/static/f/572109/24503675/1394724903587/Sailing+Yacht+Design+for+Maximum+Speed.pdf?token=5pzNaaWIFu%2F7e3pN5RiQ2e6MmmM%3D|place=Anapolis|publisher=SNAME|access-date=2 August 2020|archive-date=19 September 2020|archive-url=https://web.archive.org/web/20200919123639/https://www.sname.org/chesapeakesailingyachtsymposiumcsys/pastpapers/16thcsys|url-status=dead}}</ref><ref>{{Cite book |last=Smith |first=Doug |url=https://books.google.com/books?id=mfwDAAAAMBAJ&q=dn+ice+boat+speed+record&pg=PA20 |title=Sailing on slivers of steel |date=January–February 2004 |work= |publisher=Boy Scouts of America, Inc. |pages=18–21 |language=en}}</ref>
-1.00
-1.19
-1.43
-1.73
-2.14
-2.75
-3.73
-5.67
+=== Land-sailing craft ===
-Hull speed is not a limiting factor for an iceboat nor for high-performance multihulls.  So a boat capable of sailing at 10 degrees off the apparent wind (which is the case for many iceboats) that sails at 90 degrees to the true wind will be sailing nearly 6 times faster than the wind.  It can sail slightly faster, as a multiple of the windspeed, if it sails at a greater angle off the true wind. <ref>The maximum multiple of windspeed is achieved at an angleof 90+alpha off the true wind.  For alpha = 45, the maximum multiple of windspeed is 1.41 at an angle of 135 degrees off the true wind.</ref>
+By sailing downwind at 135° off the wind, a [[Land sailing|land-sailing craft]] can sail much faster than the wind.<ref name="nalsa faq3">{{cite web| url=http://www.nalsa.org/faq.htm#3)%20How%20do%20they%20go%20faster%20than%20the | title = Frequently Asked Questions | publisher = North American Land Sailing Association | author = Bob Dill | date = July 13, 2003 | access-date=2010-08-25}}</ref> The [[velocity made good]] downwind is often over twice as fast compared to the same craft sailing directly downwind.<ref name="nalsa faq3" /> In 2009, the world land speed record for a wind-powered vehicle was set by the sailing craft, ''[[Greenbird]]'', sailing at about three times the speed of the wind<ref name="nalsa record">The record was {{convert|126|mph|kn km/h|abbr=on}} with winds of {{convert|30|-|50|mph|km/h|abbr=on}}, see {{cite web|title=Measurement report for Speed Record Attempt Made by Richard Jenkins in the Yacht Greenbird on March 26, 2008 |url=http://www.nalsa.org/MeasuremantReport/MeasuremantReport.html | publisher = North American Land Sailing Association | author = Bob Dill | date = April 5, 2009 | access-date = 2010-08-25}}</ref> with a recorded top speed of {{convert|202.9|km/h|mi/h}}.<ref>{{cite web |last= |date=March 27, 2009 |title=Wind-powered car breaks record |url=http://news.bbc.co.uk/2/hi/technology/7968860.stm |access-date=2017-01-28 |publisher=BBC New, UK}}</ref>
+<gallery mode="packed" heights="200px" caption="Other high-performance sailing craft ">
+File:DN ice boat--Ice Nine--Lake Sunapee NH.jpg|[[International DN|DN class]] ice boat
+File:LandYacht.jpg|[[Land sailing|Land-sailing craft]]
+</gallery>
+== Apparent wind sailing ==
-However, most sailing is not done in order to achieve a maximum speed, but in order to go from one point to another.  In most sailboat racing, the objective is to sail a certain distance directly upwind (to a point called the upwind mark), and then to return downwind, as fast as possible.
+Whereas iceboats have been able to exceed the speed of the wind, both upwind and downwind for a century, this capability only became routine with the evolution of 18ft Skiffs in the third quarter of the 20th century when their speed tripled from that of the 1950s. Craft that sail faster than the speed of the wind, downwind as well as upwind, are capable of tacking downwind because the [[apparent wind]] is always ahead of the mast. This led to the concept of "apparent wind sailing".<ref name=":0" />
+=== Apparent wind ===
-Since sailboats cannot sail directly into the wind, they must [[tacking_(sailing)|tack]]. This lengthens the course, thus the boat takes longer to reach the upwind mark than it would if it could have sailed directly towards it.
+{{Main|Apparent wind}}
+[[File:Ice boat apparent wind on different points of sail.jpg|thumb|Apparent wind, V<sub>A</sub>, 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 (C). Because of a small ''β'', the sail is sheeted in for all three points of sail.|alt=]]
+Apparent wind is the wind velocity (direction and speed), V<sub>A</sub>, measured aboard a moving sailing craft; it is the net effect ([[Euclidean vector#Addition and subtraction|vector sum]]) of the ''boat wind'', V<sub>B</sub>—the air flow over the craft induced by its speed over the earth (equal to in magnitude, but opposite in direction to the craft's speed)—and the ''true wind'', V<sub>T</sub>. The apparent wind measured aboard a craft under power, traveling in calm conditions, V<sub>T</sub> = 0 knots, would come from directly ahead and at a speed that is the same as the boat speed over the bottom (V<sub>A</sub> = V<sub>B</sub> + 0 = V<sub>B</sub>). If the craft travels at V<sub>B</sub> = 10 knots with a tailwind of V<sub>T</sub> = -5 knots, it experiences an apparent wind of V<sub>A</sub> =  5 knots directly on the bow (V<sub>A</sub> = V<sub>B</sub> + V<sub>T</sub> = 10 − 5). The apparent wind experienced by a stationary craft is the true wind speed. If a craft proceeds at 90° to a true wind of V<sub>T</sub> = 10 knots, itself traveling at a speed inducing V<sub>B</sub> = 10 knots, then the apparent wind angle would be 45° off the bow and the apparent wind speed would be about 14 knots, calculated as: square root [(V<sub>B</sub> )<sup>2</sup> + (V<sub>T</sub> )<sup>2</sup>] = square root [10<sup>2</sup> + 10<sup>2</sup>] = 14.14. As the craft becomes faster than the true wind, the apparent wind is always ahead of the sail.<ref name="Garrett" />
+When drag angle of the hull is negligible, the formulas for calculating V<sub>A</sub> and ''β'' (the apparent wind angle) are:<ref>{{Cite book|last=McEwen|first=Thomas|url=https://books.google.com/books?id=kdHyM6_egMwC&q=calculation+of+%22apparent+wind%22&pg=PA182|title=Boater's Pocket Reference: Your Comprehensive Resource for Boats and Boating|date=2006|publisher=Anchor Cove Publishing, Inc.|isbn=978-0-9774052-0-6|pages=182|language=en}}</ref>
-If a boat sails perpendicular to the wind, it will never reach the upwind mark. So, in racing, speed is not everything.  What counts is the [[velocity made good]], that is, the progress towards the upwind mark.  Again, simple trignometry can be used to calculate the velocity made good.  The table below shows velocity made good, again as a multiple of windspeed, and again assuming negligeable surface resistance:
+* V<sub>A</sub> = square root {[V<sub>T</sub> cos (90° – true wind angle)]<sup>2</sup> + [V<sub>T</sub> sin (90° – true wind angle) +  V<sub>B</sub>]<sup>2</sup>}
-Of course real boats cannot equal those performances, although iceboats can come close to them.  Indeed iceboats can make good both upwind and downwind at speeds far greater than the wind.  And some extreme design boats can even sail downwind faster than the wind - although this is not intuitively obvious.<ref>http://terrytao.wordpress.com/2009/03/23/sailing-into-the-wind-or-faster-than-the-wind/</ref>
+* ''β'' = 90° – arctan {[V<sub>T</sub> sin (90° – true wind angle) +  V<sub>B</sub>] /  [V<sub>T</sub> cos (90° – true wind angle)]}
+==== Sail power ====
-Indeed, it is even possible to conceive of a boat that can sail dead downwind faster than the wind.  At first, this seems impossible.  But consider a boat that has a very large spinnaker and that drags behind it a propeller-driven electric power generator.  The spinnaker can be made suffiently large so that the boat sails nearly as fast as the wind despite the drag from the power generator.  Suppose that the generated power is stored in a batteries.  After a while, the boat can lower its sails and use the power from the batteries to run a propeller to advance faster than the wind.  Thus, on average, the boat can sail dead downwind faster than the wind.
+{{Main|Forces on sails}}
+A sail generates [[Lift (force)|lift]] with a [[Forces on sails#Components of force: lift vs. drag and driving vs. lateral force|forward propulsive component]] and a sideways component, based on an optimum [[angle of attack]] that is constrained by the apparent wind, V<sub>A</sub>, being forward of and approximately aligned with the sail.<ref>{{Citation |first=G.K. |last=Batchelor |author-link=George Batchelor |title=An Introduction to Fluid Dynamics |year=1967 |publisher=Cambridge University Press |isbn=978-0-521-66396-0 |pages=14–15 }}</ref><ref>Klaus Weltner ''A comparison of explanations of the aerodynamic lifting force'' Am. J. Phys. 55(1), January 1987 pg 52</ref>
+<gallery mode="packed" heights="200px">
-This scenario is highly theoretical and it would be difficult to achieve it in practice because of the high resistance of water.  But a sail powered cart running on wheels, on a flat surface, has much less resistance.  And indeed, a cart that ingeniously uses a propeller linked to its wheels (without batteries or electrical power generators) to sail dead downwind faster than the wind has been built and demonstrated.<ref>http://wordmunger.com/?p=1002</ref>
+File:Sail Total Force decomposed as Lift and Drag.jpg|Decomposition of wind force acting on a sail, generating lift.<br />(F<sub>T</sub> = Total aerodynamic force, L = Lift<br />D =Drag, ''α'' = angle of attack)
+File:Resolution of Total Force on sails into Lift and Drag and Forward and Lateral Force.jpg|Conversion of lift into propulsion. <br />(F<sub>R</sub> = Propulsive force, F<sub>LAT</sub> = Sideways force)
+</gallery>
+==== Beta theorem ====
+[[File:Boatforcestop.svg|thumb|''β'' is the apparent wind angle from course over the water.<ref name="Garrett" />]]
+Garrett introduces the beta theorem (or course theorem) as a way to understand how apparent wind angle results from the interplay between the driving force from the wind and the resisting force from the water (or hard surface), the result of the net effect of two counteracting foils, the sail in the air and the keel in the water. When one resolves the ratio of [[lift (force)|lift]] to drag for each in its medium, the resulting motion of the sailing craft resolves to an angle, ''beta'' (''β''), between the apparent wind and the course over the water. The hull (below the water) and the sailing rig (above the water) each have drag angle with respect to the medium flowing past them (water or air), they are ''λ'' and ''α<sub>m</sub>'' in the accompanying diagram. The sum of those two drag angles are equal to ''β,'' the angle between the apparent wind and the course sailed (''β'' = ''λ'' + ''α<sub>m</sub>''). This theorem applies for every point of sail. A small ''β'' denotes high efficiency and a potential for high speed.<ref name="Garrett">{{cite book|last=Garrett|first=Ross|url=https://books.google.com/books?id=0VLXORumEF4C&q=sail+faster+than+the+wind&pg=PA68|title=The Symmetry of Sailing: The Physics of Sailing for Yachtsmen|date=1996|publisher=Sheridan House, Inc.|isbn=978-1-57409-000-0|pages=268}}</ref> As forward velocity increases, ''β'' becomes smaller; on sailing craft with effective underwater foils the drag angle of the hull, ''λ'', becomes smaller with increased speed, it becomes negligible with hydrofoiling craft, and essentially nonexistent for ice boats and land sailing craft.<ref>{{Cite book|last=Kimball|first=John|url=https://books.google.com/books?id=Xe_i23UL4sAC&q=equation+for+%22apparent+wind%22|title=Physics of Sailing|date=2009-12-22|publisher=CRC Press|isbn=978-1-4200-7377-5|language=en}}</ref>
+==== Apparent-wind-angle limit ====
-==Notes==
+[[File:Speed ratio graph for high-performance sailing craft.png|thumb|Total drag angle (''β'' ≈ apparent wind angle) for high-performance sailing craft as a ratio of V<sub>B</sub> to V<sub>T</sub> at a course of 135° off the wind, achieved by such craft, as shown.<ref name=":0" />]]
-{{reflist}}
+Given an ideal circumstance of a frictionless surface and an airfoil that can develop power, there is no theoretical limit to how fast a sailing craft can travel off the wind as the apparent wind angle becomes ever smaller. In reality, both sail efficiency and friction provide an upper limit. Speed is determined by the ratio of power developed by the sail over power lost through various forms of drag (e.g. surface drag and aerodynamic drag). Ideally a smaller sail is better, as speeds increase. Unfortunately, a small sail diminishes the ability for a craft—even an iceboat—to accelerate to speeds faster than the wind. The principal limit to speed in high-performance sailing craft is [[Parasitic drag#Form drag|form drag]]. Efforts to overcome this limit is evident in the streamlined hulls of high-performance iceboats and the improvements in drag reduction on planing dinghies. A fast iceboat can achieve an apparent wind of 7.5° and a speed of six times the true wind speed on a course that is 135° off the wind. Bethwaite suggests this might be a practical limit for a craft powered by sails.<ref name=":0" />
+=== Points of sail ===
+{{Main|Point of sail}}
+The [[Point of sail|points of sail]] at which high-performance sailing craft can achieve highest speeds and achieve the best speed made good<ref name=":1">{{Cite book |last=Walker |first=George K. |url=https://www.google.com/books/edition/Definitions_for_the_Law_of_the_Sea/zN8FBnxT8eEC?hl=en&gbpv=1&dq=course+made+good+definition&pg=PA303&printsec=frontcover |title=Definitions for the Law of the Sea: Terms Not Defined by the 1982 Convention |date=2011-10-28 |publisher=Martinus Nijhoff Publishers |isbn=978-90-04-21160-5 |pages=158, 303 |language=en}}</ref> over a course span between a ''beam reach'' (90° to the ''[[Apparent wind|true wind]]'') and a ''broad reach'' (about 135° away from the true wind). According to Bethwaite, having made comparative measurements in a true wind of {{convert|15|kn}}, a displacement [[Soling]] can achieve speeds slightly higher than the true wind and sail 30° off the apparent wind, whereas a planing 18ft Skiff achieves speeds of almost {{convert|30|kn}} at an apparent wind of 20° and an iceboat can achieve {{convert|67|kn||abbr=}} at an apparent wind of 8°.<ref name="Bethwaite" />
+Under apparent wind sailing, the objective is to keep the apparent wind as far forward as practical for the course sailed in order to attain the fastest course made good<ref name=":1" /> to the objective. This requires a craft that can exceed the true windspeed, both upwind and downwind; this allows the apparent wind to remain well ahead of the sail on the courses sailed, the fastest of which are reaches. To be avoided is heading too far downwind, where the apparent wind moves behind the sail and the speed drops below the true windspeed as the course trends from a broad reach to running square (dead down wind).<ref name=":0" />
+==== Upwind ====
+Depending on the craft sailed, the course made good into the wind may trend away from its closest point into the wind in order to allow the craft to sail at optimum speed.<ref name=":0" /> Bethwaite explains that high-speed sailing demands independent action of both the tiller and the mainsheet, whereby the person at the helm avoids responding to gusts and, instead, eased the mainsheet as needed, thus increasing the boat's velocity made good over the previous technique of pointing the craft more into the wind.<ref name=":2">{{Cite book|last=Bethwaite|first=Frank|url=https://books.google.com/books?id=jRB8AAAAQBAJ&q=bethwaite+high+performance+sailing|title=Fast Handling Technique|date=2013-05-12|publisher=A&C Black|isbn=978-1-4081-7860-7|location=New York|pages=5–6|language=en}}</ref>
+==== Off the wind ====
+According to Bethwaite, sailing off the true wind at speeds faster than the wind (with the apparent wind forward of the sail) demands a different reaction to gusts than previously employed.  Whereas a traditional sailor might reflexively steer into the apparent wind in a gust, the correct response while sailing off wind, faster than the true wind speed is to veer away from the gust, heading more downwind. This has the doubly beneficial effect of relieving the heeling force of the gust and allowing the craft to sail yet faster off the wind.<ref name=":2" />
+== See also ==
+*[[Forces on sails]]
+*[[Wind-powered vehicle]]
+== References ==
+{{Reflist|colwidth=30em}}
+== External links ==
+* [http://www.sailspeedrecords.com/ World Sailing Speed Record Council]
+* [http://www.nalsa.org/ North American Land Sailing Association]
+* [http://www.iceboat.org/ The Four Lakes Ice Yacht Club]
+[[Category:Sailing]]
+[[Category:Marine propulsion]]