A catamaran (//) (informally, a "cat") 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 sailboat. Catamaran is from a Tamil word "Kattumaram" which means logs tied together.
Catamarans typically have less hull volume, higher 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.
Catamarans range in size from small (sailing or rowing vessels) to large (naval ships and car ferries). The structure connecting a catamaran's two hulls ranges from a simple frame strung with webbing to support the crew to a bridging superstructure incorporating extensive cabin and/or cargo space.
Catamaran-type vessels were first developed as early as 1500 BCE by the Polynesian peoples. These early examples were likely related to outrigger canoes and consisted of two canoes bound together with a wooden frame, sometimes accompanied by a sail. Despite their simplicity they were nonetheless effective, allowing seafaring Polynesians to voyage to distant Pacific islands.
Catamarans were seldom constructed in the West before the 19th century, but they were in wide use as early as the 5th century by the Tamil people of Tamil Nadu, South India. The word "catamaran" is derived from the Tamil word, kattumaram (கட்டுமரம்), which means "logs bound together." The 17th-century English adventurer and privateer William Dampier encountered the Tamil people of southeastern India during his first circumnavigation of the globe. He was the first to write in English about the watercraft he observed in use there. In his 1697 account of his trip, A New Voyage Round the World, he wrote,
On the coast of Malabar they call them Catamarans. These are but one Log, or two, sometimes of a sort of light Wood ... so small, that they carry but one Man, whose legs and breech are always in the Water.
The first documented example of double-hulled craft in Europe was designed by William Petty in 1662 to sail faster, in shallower waters, in lighter wind, and with fewer crew than other vessels of the time. However, the unusual design met with skepticism and was not a commercial success.
The design remained relatively unused in the West for almost 160 years until the early 19th-century, when the Englishman Mayflower F. Crisp built a two-hulled merchant ship in Rangoon, Burma. The ship was christened Original. Crisp described it as "a fast sailing fine sea boat; she traded during the monsoon between Rangoon and the Tenasserim Provinces for several years".
Later that century, the American Nathanael Herreshoff constructed a double-hulled sailing boat of his own design (US Pat. No. 189,459). The craft, Amaryllis, raced at her maiden regatta on June 22, 1876, and performed exceedingly well. Her debut demonstrated the distinct performance advantages afforded to catamarans over the standard monohulls. It was as a result of this event, the Centennial Regatta of the New York Yacht Club, that catamarans were barred from regular sailing classes, and this remained the case until the 1970s.
In 1936 Eric de Bisschop built a Polynesian "double canoe" in Hawaii and sailed it home to a hero's welcome in France. In 1939, he published his experiences in a book, Kaimiloa, which was translated into English in 1940.
The Prout Brothers, Roland and Francis, experimented with catamarans in 1949 and converted their 1935 boat factory in Canvey Island, Essex (England), to catamaran production in 1954. Their Shearwater catamarans won races easily against the monohulls. Yellow Bird, a 1956-built Shearwater, raced successfully by Francis Prout in the 1960s, is in the collection of the National Maritime Museum Cornwall.
In the mid-twentieth century, beachcats became a widespread category of sailing catamarans, owing to their ease of launching and mass production. In California, a maker of surfboards, Hobie Alter, produced the 250-pound (110 kg) Hobie 14 in 1967, and two years later the larger and even more successful Hobie 16. As of 2016, the Hobie 16 was still being produced with more than 100,000 having been manufactured.
The Tornado catamaran was designed by three Englishmen for a crew of two in 1967 as an Olympic catamaran candidate. At the Olympic Catamaran Trials of the International Yacht Racing Union, IYRU, it outperformed the other challengers for the role and was selected for the multihull discipline in the Olympic Games from 1976 through 2008. It was redesigned in 2000 and remains one of the fastest double-handed catamaran models.
Catamarans have two distinct primary performance characteristics that distinguish them from displacement monohull vessels: lower resistance to passage through the water and greater stability (initial resistance to capsize). Choosing between a monohull and catamaran configuration includes considerations of carrying capacity, speed, and efficiency.
At low to moderate speeds, a lightweight catamaran hull experiences resistance to passage through water that is approximately proportional to the square of its speed. A displacement monohull, by comparison, experiences resistance that is at least the cube of its speed. This means that a catamaran would require four times the power in order to double its speed, whereas a monohull would require eight times the power to double its speed, starting at a slow speed. For powered catamarans, this implies smaller power plants (although two are typically required). For sailing catamarans, low forward resistance allows the sails to derive power from attached flow, their most efficient mode—analogous to a wing—leading to the use of wingsails in racing craft.
Catamarans rely primarily on form stability to resist heeling and capsize. Comparison of heeling stability of a rectangular-cross section monohull of beam, B, compared with two catamaran hulls of width B/2, separated by a distance, 2×B, determines that the catamaran has an initial resistance to heeling that is seven times that of the monohull. Compared with a monohull, a cruising catamaran sailboat has a high initial resistance to heeling and capsize—a fifty-footer requires four times the force to initiate a capsize than an equivalent monohull.
One measure of the trade-off between speed and carrying capacity is the displacement Froude number (FnV), compared with calm water transportation efficiency. FnV applies when the waterline length is too speed-dependent to be meaningful—as with a planing hull. It uses a reference length, the cubic root of the volumetric displacement of the hull, V, where u is the relative flow velocity between the sea and ship, and g is acceleration due to gravity:
Large merchant vessels have a FnV between one and zero, whereas higher-performance powered catamarans may approach 2.5—denoting a higher speed per unit volume for catamarans. Each type of vessel has a corresponding calm water transportation efficiency, with large transport ships being in the range of 100–1,000, compared with 11-18 for transport catamarans—denoting a higher efficiency per unit of payload for monohulls.
Sailing catamarans have been noted for incorporating technological advances over traditional monohull craft. These include foils that lift racing catamarans out of the water, capacious and stable cruising vessels, and racers that have achieved average speeds on the open ocean, comparable to much larger vessels.
Recreational and sport catamarans typically are designed to have a crew of two and be launched and landed from a beach. Most have a trampoline on the bridging structure, a rotating mast and full-length battens on the mainsail. Performance versions often have trapezes to allow the crew to hike out and counterbalance capsize forces during strong winds on certain points of sail.
For the 33rd America's Cup, both the defender and the challenger built 90-foot (27 m) long multihulls. Société Nautique de Genève, defending with team Alinghi, sailed a catamaran. The challenger, BMW Oracle Racing, used a trimaran, replacing its soft sail rig with a towering wing sail—the largest sailing wing ever built. In the waters off Valencia, Spain in February 2010, the BMW Oracle Racing trimaran with its powerful wing sail proved to be superior. This represented a break from the traditional monohulls that had always been sailed in previous America's Cup series.
On San Francisco Bay, the 2013 America's Cup was sailed in 72-foot (22 m) long AC72 catamarans (craft set by the rules for the 2013 America's Cup). Each yacht employed hydrofoils and a wing sail. The regatta was won 9-8 by Oracle Team USA against the challenger, Emirates Team New Zealand, in fifteen matches because Oracle Team USA had started the regatta with a two-point penalty.
Cruising sailors must make trade-offs among volume, useful load, speed, and cost in choosing a boat. Choosing a catamaran offers increased speed at the expense of reduced load per unit of cost. Howard and Doane describe the following tradeoffs between cruising monohulls and catamarans: A long-distance, offshore cruising monohull may be as short as 30 feet (9.1 m) for a given crew complement and supporting supplies, whereas a cruising catamaran would need to be 40 feet (12 m) to achieve the same capacity. In addition to greater speed, catamarans draw less water than do monohulls—little as 3 feet (0.91 m)—and are easier to beach. Catamarans are harder to tack and take up more space in a marina. Cruising catamarans entail added expense for having two engines and two rudders. Tarjan adds that cruising catamarans boats can maintain a comfortable 300 nautical miles (350 mi; 560 km) per day passage, with the racing versions recording well over 400 nautical miles (460 mi; 740 km) per day. In addition, they do not heel more than 10-12 degrees, even at full speed on a reach.
Yachting has seen the development of multihulls over 100 feet (30 m) in length. "The Race" helped precipitate this trend; it was a circumnavigation challenge which departed from Barcelona, Spain, on New Year's Eve, 2000. Because of the prize money and prestige associated with this event, four new catamarans (and two highly modified ones) over 100 feet (30 m) in length were built to compete. The largest, PlayStation, owned by Steve Fossett, was 125 feet (38 m) long and had a mast which was 147 feet (45 m) above the water. Virtually all of the new mega-cats were built of pre-preg carbon fiber for strength and the lowest possible weight. The top speeds of these boats can approach 50 knots (58 mph; 93 km/h). The Race was won by the 33.50 m (109.9 ft)-long catamaran Club Med skippered by Grant Dalton. It went round the globe in 62 days at an average speed of 18 knots (21 mph; 33 km/h).
A catamaran configuration fills a niche for powered vessels, where speed and sea-kindliness is favored over bulk capacity. In larger vessels, this niche favors car ferries and military vessels for patrol or operation in the littoral zone. Two advances over the traditional catamaran are the small-waterplane-area twin hull (SWATH) and the wave-piercing configuration—the latter having become a widely favored design.
An outgrowth of the popularity of cruising sailing catamarans are powered catamarans, which share many of the amenities found in a sail cruising catamaran. The saloon typically spans two hulls wherein are found the staterooms and engine compartments. As with sailing catamarans, this configuration minimizes boat motion in a seaway.
The Swiss-registered wave-piercing catamaran, Tûranor PlanetSolar, which was launched in March 2010, is the world's largest solar powered boat. It completed a circumnavigation of the globe in 2012.
The 1970s saw the introduction of catamarans as a high-speed ferries, as pioneered by Westermoen Hydrofoil in Mandal, Norway, which launched the Westamaran design in 1973. The Stena Voyager was an example of a large, fast ferry, typically traveling at a speed of 46 miles per hour (74 km/h), although it was capable of doing over 70 miles per hour (110 km/h).
Military Sealift Command currently operates several Expionary Fast Transport catamarans which are owned by the U.S. Navy. These are employed for the high speed transport of military cargo and are able to get into shallow ports due to their small draft.
The small-waterplane-area twin hull (SWATH) configuration reduces wave-generating resistance by moving displacement volume below the waterline, using a pair of tubular, submarine-like hulls, connected by pylons to the bridge deck with a narrow waterline cross-section. The submerged hulls are minimally affected by waves. The SWATH form was invented by Canadian Frederick G. Creed, who presented his idea in 1938 and was later awarded a British patent for it in 1946. It was first used in the 1960s and 1970s as an evolution of catamaran design for use as oceanographic research vessels or submarine rescue ships. In 1990, the US Navy commissioned the construction of a SWATH ship to test the configuration.
SWATH vessels compare with conventional powered catamarans of equivalent size, as follows:
Wave-piercing catamarans employ a low-buoyancy bow on each hull that is pointed at the water line and rises aft, up to a level, to allow each hull to pierce waves, rather than ride over them. This allows higher speeds through waves than for a conventional catamaran. They are distinguished from SWATH catamarans, in that the buoyant part of the hull is not tubular. The spanning bridge deck may be configured with some of the characteristics of a normal V-hull, which allows it to penetrate the crests of waves.
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The catamarans for whitewater sports are widely spread in post-Soviet countries. They consists of two inflatable hulls connected with a lattice scaffold. The frame of the tourist catamaran can be made of both - aluminum (duralumin) pipes, and from felled tree trunks. The inflatable part has two layers - airtight balloon with inflation holes and shell made of dense tissue, protecting the balloon from mechanical damage.
Advantages of such catamarans are light weight, compactness and convenience in transportation (the whole product is packed in one pack-backpack, suitable for air traffic standards), the speed of assembly (10-15 minutes for the inflation). Landing on such a catamaran can be a raft-type, as well as a sports knee-type.
See Fig. 2.1 'Slender' and 'Swath' figures.