A sailing hydrofoil , hydrofoil sailboat, or hydrosail is a sailboat with wing-like foils mounted under the hull. As the craft increases its speed the hydrofoils lift the hull up and out of the water, greatly reducing wetted area, resulting in decreased drag and increased speed. A sailing hydrofoil can achieve speeds exceeding twice the wind speed.
Both monohull and multihull sailboats can be retrofitted with hydrofoils, although greater stability can be achieved by using the wider planform of a catamaran or trimaran.
Some multihulls use three foils; two main forward foils provide lift so that the boat "flies" while a horizontal foil on the rudder is trimmed to drive and control altitude. On catamarans, a single main foil can be attached between the hulls just in front of the center of gravity and at 2 degrees of incidence, spanning the tunnel with supporting struts. Hydrofoil catamarans are also called foilcats.[ citation needed ]
Multihull sailboats can also employ hydrofoils only to assist performance. Just as daggerboards and rudders are foils that enhance the control of a boat, assisting hydrofoils provide lift to the hull to reduce the wetted area without actually lifting the boat completely out of the water.
Monohull boats typically employ a "ladder" arrangement of hydrofoils splayed out with a dihedral angle of 50 degrees, with a stabilizing rudder foil. One of the earliest examples is the Monitor boat from 1957.This design offers the advantages of maximum lifting foil area at slow speeds and less at higher speeds, with rolling resistance arising from the dihedral support of the outboard ladder foils.
The most widespread use of hydrofoils in sailboats to date has been in the International Moth class. Andy Paterson of Bloodaxe boats on the Isle of Wight is widely considered to have developed the first functional foiling Moth, though his boat had three foils in a tripod arrangement. Brett Burvill sailed a narrow skiff Moth with inclined surface-piercing hydrofoils to a race win at the Moth World Championships in 2001 in Australia, which was the first time a hydrofoil Moth had won a race at a World Championship. This hydrofoil configuration was later declared illegal by the class, as it was felt to constitute a multihull, which is prohibited by class rules. Initially Ian Ward in Sydney, Australia developed the first centerline foiling Moth which demonstrated that sailing on centerboard and rudder foils alone was feasible. Subsequently, Garth and John Ilett in Perth, Australia developed a two-hydrofoil system for the Moth with active flap control for the main foil via a surface sensor. John's company Fastacraft was the first to produce a commercially available hydrofoil International Moth. Fasta Craft's Prowler design, superseded in 2008 by the F-Zero, features a carbon-fiber hull, inverted "T" foils on the centerboard and rudder, and can reach speeds of over 27 knots. Fasta Craft has since been joined in producing hydrofoil Moths by several other companies, including Bladerider, Assassin, Exocet, and Aardvark Technologies.
Although initially debated fiercely within the class, the adoption of hydrofoils has proven a success for the International Moth class, with rapid fleet growth in the years since 2001. All World Championships since 2004 have been won by hydrofoil-equipped Moths, which can become foilborne in as little as six knots of breeze when steered by an experienced sailor of lighter weight. The class rule remains open to development of all boat components including hydrofoil systems, and development within the class continues to be spurred by both commercial and individual/amateur efforts.
The first time a Laser foiled was in December 2009 by Ian Ward in Sydney, Australia. Top speeds of around 23-25kts are possible with this kit. The foils can be removed and the boat remains class legal. This foiling system is unique in that it is retractable, has flapless foils and the height sensing 'wand' is integrated within the daggerboard.
The "world's least advanced sailboat" was converted to hydrofoiling by the Chalmers University of Technology, in Sweden, in 2017.
The Optimist, only 2.3 metres in length and with a sail area of 3.3 square metres, is normally limited to speeds below 4 knots. The hydrofoils allows the optimist dinghy to achieve 12 knots in only 12 knots of wind.
The AC75 (America's Cup 75 class) is a 75 ft sailboat class, governing the construction and operation of the yachts used in the 2021 America's Cup. The boat type is a foiling monohull with canting ballasted T-wing hydrofoils mounted on port and starboard topside longitudinal drums, a centerline T-wing rudder, and no keel. Speeds of 50 knots were predicted based on computer simulations and in fact have been exceeded in the Prada Cup by the America Magic’s boat in January 2021.
Foils have been used in the America's Cup since 2013.
The GC32 is carbon fibre production hydrofoil catamaran 32 feet in length (9.75 meters). It has a top speed of about 40 knots (74 km/h; 46 mph). They are sailed in the GC32 Racing Tour, and have replaced the Extreme 40's in the Extreme Sailing Series.
The 2013 America's Cup featured daggerboard catamarans. Under the terms of the protocol, these daggerboards could not feature trim tabs, could not exceed the beam of the boat when raised and could not be adjusted when lowered, but a loophole exploited by three teams was to create T-shaped rudders and L-shaped daggerboards of which the leeward appendage serves as a hydrofoil on all points of sailing conditions in winds over 10 knots. On September 6, 2012 in Auckland, during Team New Zealand's fifth day of trials, their boat achieved 40 knots (74 km/h) with a level trim and no heeling in 17 knots of breeze.
The 2015–16 America's Cup World Series was raced with hydrofoiling AC45f catamarans, which are smaller versions of the AC72.
The 2017 America's Cup was raced in the fully foiling AC50 class.
Recent International C-class catamaran have been foiling, and further development is expected.
International A-class catamaran rule 8 initially allowed hydrofoils[ citation needed ] but was changed to specifically outlaw hydrofiols by ballot on 15 August 2001 after the measurer and president were approached by Jeremy Banks, an Australian sailor, with a hydrofoiling design[ citation needed ]. In 2010 the rule 8 was amended to allow restricted hydrofiols</ref> International A-Class Catamaran Class Rules 2010 <?ref> . The 2014 A-Class Catamaran World Titles in Takapuna New Zealand demonstrated early foiling capabilities to the class. Now the A-Class can foil stably downwind in 6 knots and upwind in 12 knots or more. Peak speeds are reported to be about 30 knots and 2.5X wind speed. The A-Class has set the standard for 4-point foiling that many classes are now adopting.
The Nacra 17 as raced at the 2016 Olympics was capable of elevated foiling under some conditions. For the 2017 World Championships, the Nacra was upgraded to a fully foiling yacht, to be raced at the 2020 Tokyo Olympics.
The Nacra F20 is a catamaran similar in design to Nacra Sailing's former 20 foot catamaran, however it is made out of carbon fiber and uses curved daggerboards as hydrofoils.
The Flying Phantom is a catamaran that uses curved daggerboards as hydrofoils.
iFLY15 is a 15-foot hydrofoil catamaran equipped with automatic foils, built by CEC Catamarans GmbH. It uses a mechanical automatic system to stabilize the horizontal trim in the longitudinal and transverse directions. Jibes are facilitated by the four T-shaped foils which are always in the water and stabilize the boat.
In the 1990s the Hobie Cat company manufactured the TriFoiler (no longer in production), a twin-sail trimaran with a mainsail on each outrigger capable of 35+ knot speeds in typical sailing conditions, making the TriFoiler the fastest production sailboat in the world. The prototype of the Hobie TriFoiler, called Longshot, was developed by brothers Dan and Greg Ketterman in conjunction with Russell Long. Though more streamlined than the Trifoiler and having smaller hydrofoils, Longshot still holds the Class A speedsailing record of 43.55 knots on a 500-meter course, set in Tarifa Spain in 1993. Until recently, it was the only existing speedsailing record held by a hydrofoil, but the recent records of Hydroptère have added to the list with record breaking runs across the English Channel.
In 1998, WindRider LLC introduced the WindRider Rave,a popular two-person trimaran hydrofoil capable of lifting off in as little as 12-13 knots of wind. The Rave is capable of sailing between 1.5 and 2 times wind speed. The boat's mainsail has no boom. The Rave broke new ground in the development of flapped foils and control systems.
Non-production experimental designs have been built:
A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains speed, the hydrofoils lift the boat's hull out of the water, decreasing drag and allowing greater speeds.
A multihull is a ship or boat with more than one hull, whereas a vessel with a single hull is a monohull.
A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture.
A catamaran is a multi-hulled watercraft featuring two parallel hulls of equal size. It is a geometry-stabilized craft, deriving its stability from its wide beam, rather than from a ballasted keel as with a monohull boat. Catamarans typically have less hull volume, smaller displacement, and shallower draft (draught) than monohulls of comparable length. The two hulls combined also often have a smaller hydrodynamic resistance than comparable monohulls, requiring less propulsive power from either sails or motors. The catamaran's wider stance on the water can reduce both heeling and wave-induced motion, as compared with a monohull, and can give reduced wakes.
A daggerboard is a retractable centreboard used by various sailing craft. While other types of centreboard may pivot to retract, a daggerboard slides in a casing. The shape of the daggerboard converts the forward motion into a windward lift, countering the leeward push of the sail. The theoretical centre of lateral resistance is on the trailing edge of the daggerboard.
Speed sailing is the art of sailing a craft as fast as possible over a predetermined route, and having its overall or peak speed recorded and accredited by a regulatory body. The term usually refers to sailing on water, even though sailing on land and ice is progressively faster because of the lower friction involved. The World Sailing Speed Record Council is the body authorized by the International Sailing Federation to confirm speed records of sailing craft on water.
The Hobie Cat is a small sailing catamaran manufactured by the Hobie Cat Company. Hobie's line of products includes surfboards, sailboats, kayaks, stand-up paddle boards, and pedalboards, although the Hobie Cat Company is known worldwide for its catamarans. Hobie also designed a successful monohull, the Hobie 33.
A beachcat is an off-the-beach class of catamaran ("cat") sailboat.
In dinghy sailing, a boat is said to be turtling or to turn turtle when the boat is fully inverted with the mast pointing down to the lake bottom or seabed. The name stems from the appearance of the upside-down boat, similar to the carapace, that is the top shell of a sea turtle. The term can be applied to any vessel; turning turtle is less frequent but more dangerous on ships than on smaller boats. Relative to monohulls, it is more hazardous on multihulls, because of their inherent stability in an inverted position. Measures can be taken to prevent a capsize from becoming a turtle.
The Topcat is a one-design sailing catamaran boat class which is divided into several boat sizes.
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. 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.
Nacra Sailing is a Dutch company that manufactures a line of small catamaran sailboats, or beachcats. NACRA was founded in 1975 to tap into the market created by Hobie Alter the founder of Hobie Cat, and several other companies offering small fiberglass catamarans designed to be sailed off the beach by a crew of one or two.
The Nacra 17 is a performance catamaran used for sailing. It was designed in 2011, went into production in 2012 and has been the focus of multihull sailing at the Olympic Games since its conception.
The Nacra F18 Infusion is a Dutch Formula 18 catamaran sailing dinghy that was designed by Morrelli & Melvin, Vink, Larsen, Young as a one-design racer and first built in 2008.
The Sol Cat 18 is a double handed multihull catamaran produced by Sol Catamarans, Inc. from 1973–1979.
The GC32 is a class of hydrofoiling catamaran, 32 feet in length and constructed of carbon fibre, with a top speed of about 40 knots. They are sailed in the GC32 Racing Tour, and have replaced the Extreme 40's in the Extreme Sailing Series.
The Hobie 17 is an American catamaran that was designed by John Wake as a single-handed racer and first built in 1985.
The Flying Phantom Essentiel,, is a French hydrofoil catamaran sailing dinghy that was designed by Gonzalo Redondo and Martin Fischer and first built in 2017.
The Nacra 20 is a catamaran sailing dinghy that was designed by Gino Morrelli and Pete Melvin as a one-design racer and first built in 1998.
The Nacra 5.2 is an American catamaran sailing dinghy that was designed by Tom Roland as a one-design racer and first built in 1975. Other that the small production run Nacra 36, the Nacra 5.2 was the first Nacra brand boat and established its reputation.