Wingsail

Last updated September 27, 2023

A wingsail, twin-skin sail^[1] or double skin sail^[2] is a variable-camber aerodynamic structure that is fitted to a marine vessel in place of conventional sails. Wingsails are analogous to airplane wings, except that they are designed to provide lift on either side to accommodate being on either tack. Whereas wings adjust camber with flaps, wingsails adjust camber with a flexible or jointed structure (for hard wingsails). Wingsails are typically mounted on an unstayed spar—often made of carbon fiber for lightness and strength. The geometry of wingsails provides more lift, and a better lift-to-drag ratio, than traditional sails. Wingsails are more complex and expensive than conventional sails.^[3]

Introduction

Wingsails are of two basic constructions that create an airfoil, "soft" and "hard", both mounted on an unstayed rotating mast.^[4] Whereas hard wingsails are rigid structures that are stowed only upon removal from the boat, soft wingsails^[5]^[6] can be furled or stowed on board.^[4]

L. Francis Herreshoff pioneered a precursor rig that had jib and main, each with a two-ply sail with leading edges attached to a rotating spar. The C Class Catamaran class has been experimenting and refining wingsails in a racing context since the 60s. Englishman, John Walker, explored the use of wingsails in cargo ships and developed the first practical application for sailing yachts in the 1990s. Wingsails have been applied to small vessels, like the Optimist dinghy and Laser, to cruising yachts, and most notably to high-performance multihull racing sailboats, like USA-17. The smallest craft have a unitary wing that is manually stepped. Cruising rigs have a soft rig that can be lowered, when not in use. High-performance rigs are often assembled of rigid components and must be stepped (installed) and unstepped by shore-side equipment.^[3]

Camber adjustment

Wingsails change camber (the asymmetry between the top and the bottom surfaces of the aerofoil), depending on tack and wind speed.^[7]^{[ page needed ]} A wingsail becomes more efficient with greater curvature on the downwind side. Since the windward side changes with each tack, so must sail curvature change. This happens passively on a conventional sail, as it fills in with wind on each tack. On a wingsail, a change in camber requires a mechanism. Wingsails also change camber to adjust for windspeed. On an aircraft, flaps increase the camber or curvature of the wing, raising the maximum lift coefficient—the lift a wing can generate—at lower air speeds (speed of the air passing over it). A wingsail has the same need for camber adjustment, as windspeed changes—a straighter camber curvature as windspeed increases, more curved as it decreases.^[3]

Mechanisms for camber adjustment are similar for soft and hard wingsails. Each employs independent leading and trailing airfoil segments that are adjusted independently for camber. More sophisticated rigs allow for variable adjustment of camber with height above the water to account for increased windspeed.^[3]^[8]

Comparison with conventional sailing rigs

The presence of rigging, supporting the mast of a conventional fore-and-aft rig limits sail geometry to shapes that are less efficient than the narrow chord of the wingsail. However, conventional sails are simple to adjust for windspeed by reefing. Wingsails typically are a fixed surface area. Conventional sails can be furled easily; some flexible wingsails can be dropped, when not in use; rigid wingsails must be removed when exposure to wind is undesirable.^[3]

Points of sail

Nielsen summarised the efficiencies of wingsails, compared with conventional sails, for different points of sail, as follows:^[3]

Close-hauled: At 30° apparent wind, the wingsail has a 10-degree angle of attack and more lift, compared to the conventional sail plan and its angles of attack of 15° for the jib and 20° for the mainsail.
Beam reach: At 90° apparent wind, the wingsail, positioned across the boat, functions efficiently as a wing, providing forward lift, whereas the jib of the conventional sail plan suffers from being difficult to shape as a wing (the main sail is still relatively efficient).
Broad reach: At 135° apparent wind, the wingsail may be eased in such a manner that it still functions efficiently as a wing, whereas the jib and main sail no longer provide lift—instead they present themselves perpendicular to the wind and provide force from drag only.

Related Research Articles

Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the water, on ice (iceboat) or on land over a chosen course, which is often part of a larger plan of navigation.

A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface.

<span class="mw-page-title-main">Jibe</span> Basic sailing maneuver, where ship turns its stern through the wind

A jibe (US) or gybe (Britain) is a sailing maneuver whereby a sailing vessel reaching downwind turns its stern through the wind, which then exerts its force from the opposite side of the vessel. Because the mainsail boom can swing across the cockpit quickly, jibes are potentially dangerous to person and rigging compared to tacking. Therefore, accidental jibes are to be avoided while the proper technique must be applied so as to control the maneuver. For square-rigged ships, this maneuver is called wearing ship.

<span class="mw-page-title-main">Backstay</span> Piece of standing rigging on a sailing vessel

A backstay is a piece of standing rigging on a sailing vessel that runs from the mast to either its transom or rear quarter, counteracting the forestay and jib. It is an important sail trim control and has a direct effect on the shape of the mainsail and the headsail. Backstays are generally adjusted by block and tackle, hydraulic adjusters, or lines leading to winches.

<span class="mw-page-title-main">Staysail</span>

A staysail ("stays'l") is a fore-and-aft rigged sail whose luff can be affixed to a stay running forward from a mast to the deck, the bowsprit, or to another mast.

A spinnaker is a sail designed specifically for sailing off the wind on courses between a reach to downwind. Spinnakers are constructed of lightweight fabric, usually nylon, and are often brightly colored. They may be designed to perform best as either a reaching or a running spinnaker, by the shaping of the panels and seams. They are attached at only three points and said to be flown.

A mainsail is a sail rigged on the main mast of a sailing vessel.

Running rigging is the rigging of a sailing vessel that is used for raising, lowering, shaping and controlling the sails on a sailing vessel—as opposed to the standing rigging, which supports the mast and bowsprit. Running rigging varies between vessels that are rigged fore and aft and those that are square-rigged.

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 and its shape,. Sails are typically constructed out of flexible material that is shaped by various means, while in use, to offer an appropriate airfoil, according to the strength and apparent direction of the wind. A variety of features and fittings allow the sail to be attached to lines and spars.

Reefing reduces the area of a sail, usually by folding or rolling one edge of the canvas in on itself and attaching the unused portion to a spar or a stay, as the primary measure to preserve a sailing vessel's stability in strong winds. Restoring full sail area is termed shaking out a reef.

<span class="mw-page-title-main">Fractional rig</span> Sailing rig type

A fractional rig on a sailing vessel consists of a foresail, such as a jib or genoa sail, that does not reach all the way to the top of the mast.

The junk rig, also known as the Chinese lugsail, Chinese balanced lug sail, or sampan rig, is a type of sail rig in which rigid members, called battens, span the full width of the sail and extend the sail forward of the mast.

A mast-aft rig is a sailboat sail-plan that uses a single mast set in the aft half of the hull. The mast supports fore-sails that may consist of a single jib, multiple staysails, or a crab claw sail. The mainsail is either small or completely absent. Mast-aft rigs are uncommon, but are found on a few custom, and production sailboats.

<span class="mw-page-title-main">Roller furling</span>

Roller furling is a method of furling a yacht's staysail by rolling the sail around a stay. Roller furling is typically used for foresails such as jibs or genoas.

An asymmetrical spinnaker is a sail used when sailing downwind. Also known as an "asym", "aspin", or "A-sail" it can be described as a cross between a genoa jib and a spinnaker. It is asymmetric like a genoa, but, the asymmetrical spinnaker is not attached to the forestay over the full length of its luff, being rigged like a spinnaker. The asymmetrical spinnaker has a larger camber than a genoa, making it optimal for generating lift at larger angles of attack, but the camber is significantly less than that of a spinnaker.

USA-17 is a sloop rigged racing trimaran built by the American sailing team BMW Oracle Racing to challenge for the 2010 America's Cup. Designed by VPLP Yacht Design with consultation from Franck Cammas and his Groupama multi-hull sailing team, BOR90 is very light for her size being constructed almost entirely out of carbon fiber and epoxy resin, and exhibits very high performance being able to sail at 2.0 to 2.5 times the true wind speed. From the actual performance of the boat during the 2010 America's Cup races, it can be seen that she could achieve a velocity made good upwind of over twice the wind speed and downwind of over 2.5 times the wind speed. She can apparently sail at 20 degrees off the apparent wind. The boat sails so fast downwind that the apparent wind she generates is only 5-6 degrees different from that when she is racing upwind; that is, the boat is always sailing upwind with respect to the apparent wind. An explanation of this phenomenon can be found in the article on sailing faster than the wind.

Forces on sails result from movement of air that interacts with sails and gives them motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles. Similar principles in a rotating frame of reference apply to windmill sails and wind turbine blades, which are also wind-driven. They are differentiated from forces on wings, and propeller blades, the actions of which are not adjusted to the wind. Kites also power certain sailing craft, but do not employ a mast to support the airfoil and are beyond the scope of this article.

Ljungström sailboats were created by the Swedish engineer Fredrik Ljungström, who was interested in sailing since childhood. A "Ljungström sailboat" typically has a "circular arc" hull and a "Ljungström rig". A Ljungström rig mast has no mast stays. The mast rotates on two ball bearings often flying double mainsails, with no foresails. In their time the Ljungström sailboats were a minor revolution as they were fast, safe and easy to sail as well as relatively easy and affordable to produce.

<span class="mw-page-title-main">Sail</span> Fabric or other surface supported by a mast to allow wind propulsion

A sail is a tensile structure, which is made from fabric or other membrane materials, that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments, usually in a three- or four-sided shape.

On sailboats, a sail batten is a flexible insert in a sail, parallel to the direction of wind flow, that helps shape its qualities as an airfoil. Battens are long, thin strips of material, historically wooden but today usually fiberglass, vinyl, or carbon fiber, used to support the roach of a sail. They are also used on tall ships to form the ladders up the shrouds in a fashion similar to ratlines.

References

↑ Reed, Dave (August 27, 2019). "Intel on the AC75's Twin-Skin Main". Sailing World. Retrieved 2020-12-28.
↑ Griffin, Jack (August 27, 2018). "AC75 Double Luff Mainsail". www.sail-world.com. Retrieved 2020-12-28.
1 2 3 4 5 6 Nielsen, Peter (May 14, 2014). "Have Wingsails Gone Mainstream?". Sail. Retrieved 2015-01-24.
1 2 Nielsen, Peter (August 2, 2017). "Have Wingsails Gone Mainstream?". Sail Magazine. Retrieved 2021-03-24.
↑ Heppell, Toby (2021-02-26). "America's Cup: Our analysis of INEOS' development". Yachting World. Retrieved 2021-03-24.{{cite magazine}}: CS1 maint: url-status (link)
↑ Reynolds, Pat (2016-01-13). "What's In A Rig? - Wingsail". American Sailing Association. Retrieved 2021-03-24.
↑ Houghton, E. L.; Carpenter, P. W. (2003). Butterworth Heinmann (ed.). Aerodynamics for Engineering Students (5th ed.). ISBN 0-7506-5111-3.
↑ Widnall, Sheila; Cornwell, Hayden; Williams, Peter (2014). "Effects of Spanwise Flexibility on Lift and Rolling Moment of a Wingsail". Widnall. Massachusetts Institute of Technology Department of Aeronautics and Astronautics. hdl:1721.1/92344.

External links

Media related to Wings (sailing) at Wikimedia Commons

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[1] Reed, Dave (August 27, 2019). "Intel on the AC75's Twin-Skin Main". Sailing World. Retrieved 2020-12-28.

[2] Griffin, Jack (August 27, 2018). "AC75 Double Luff Mainsail". www.sail-world.com. Retrieved 2020-12-28.

[Sail-3] 1 2 3 4 5 6 Nielsen, Peter (May 14, 2014). "Have Wingsails Gone Mainstream?". Sail. Retrieved 2015-01-24.

[:0-4] 1 2 Nielsen, Peter (August 2, 2017). "Have Wingsails Gone Mainstream?". Sail Magazine. Retrieved 2021-03-24.

[5] Heppell, Toby (2021-02-26). "America's Cup: Our analysis of INEOS' development". Yachting World. Retrieved 2021-03-24.{{cite magazine}}: CS1 maint: url-status (link)

[6] Reynolds, Pat (2016-01-13). "What's In A Rig? - Wingsail". American Sailing Association. Retrieved 2021-03-24.

[houghton&carpenter-7] Houghton, E. L.; Carpenter, P. W. (2003). Butterworth Heinmann (ed.). Aerodynamics for Engineering Students (5th ed.). ISBN 0-7506-5111-3.

[Widnall-8] Widnall, Sheila; Cornwell, Hayden; Williams, Peter (2014). "Effects of Spanwise Flexibility on Lift and Rolling Moment of a Wingsail". Widnall. Massachusetts Institute of Technology Department of Aeronautics and Astronautics. hdl:1721.1/92344.

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