High-performance sailing

Frank Bethwaite offers the following chronology of key advances in sailing technology that provided the essential elements of high-performance sailing: • 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 ==

catamaran with wingsail in the 2013 America's CupHigh-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. Other skiffs that can sail faster than the wind include the 29er, and 49er, both designed by Julian Bethwaite. 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. They proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0. The Extreme 40 catamaran can sail at in winds. The high-performance International C-Class Catamaran can sail at twice the speed of the wind. 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. Other foiling catamarans include A-Class, C-Class, Nacra 17, Nacra F20, and GC32. In 2009, hydrofoil trimaran, Hydroptère, set the world speed sailing record on water at , sailing at about 1.7 times the speed of the wind. In late 2012, Vestas Sailrocket 2 achieved a new outright world speed record of on water, at around 2.5 times the speed of the wind. Iceboats Iceboats on the Hudson River of New York in the second half of the 19th century were as long as and sailed as fast as , 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. and for a classic iceboat: Debutaunte, . Land-sailing craft By sailing downwind at 135° off the wind, a land-sailing craft can sail much faster than the wind. The velocity made good downwind is often over twice as fast compared to the same craft sailing directly downwind. with a recorded top speed of . File:DN ice boat--Ice Nine--Lake Sunapee NH.jpg|DN class ice boat File:LandYacht.jpg|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". • VA = square root {[VT cos (90° – true wind angle)]2 + [VT sin (90° – true wind angle) + VB]2} • β = 90° – arctan {[VT sin (90° – true wind angle) + VB] / [VT 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, VA, being forward of and approximately aligned with the sail. File:Sail Total Force decomposed as Lift and Drag.jpg|Decomposition of wind force acting on a sail, generating lift.(FT = Total aerodynamic force, L = LiftD =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. (FR = Propulsive force, FLAT = Sideways force) Beta theorem ) and a broad reach'' (about 135° away from the true wind). According to Bethwaite, having made comparative measurements in a true wind of , 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 at an apparent wind of 20° and an iceboat can achieve at an apparent wind of 8°. 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. == See also ==