trimaran

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"BMW Oracle" is a 90 ft long trimaran, type BOR90, one of the world's most advanced yacht racing machines.

A trimaran is a multihulled boat consisting of a main hull (vaka) and two smaller outrigger hulls (amas), attached to the main hull with lateral struts (akas). The design and names for the trimaran components are derived from the original proa constructed by native Pacific Islanders.

History

The first trimarans were built by indigenous Polynesians almost 4,000 years ago, and much of the current terminology is inherited from them. Multihull sailboats (catamarans and trimarans) gained favor during the 1960s and 1970s. Modern recreational trimarans are rooted in the same homebuilt tradition as other multihulls but there are also a number of production models on the market. A number of trimarans in the 19 – 36 foot lengths have been designed over the last 30 years to be accommodated on a road trailer. These include the original Farrier - Corsair folding trimarans - and original John Westell swing-wing folding trimaran (using the same folding system later adopted also on Quorning Dragonfly) and like trimarans. Many sailboat designers have also designed demountable trimarans that are able to be trailered (like the SeaCart 30 by Oceanlake Marine ^[1]).

The trimaran design is also becoming more widespread as a passenger ferry. In 2005 the 127 metre (417 ft) trimaran Benchijigua Express was delivered by Austal to Spanish ferry operator Fred.Olsen, S.A. for service in the Canary Islands. Capable of carrying 1280 passengers and 340 cars, or equivalents, at speeds up to 40 knots, this boat was the longest aluminum ship in the world at the time of delivery.^[2] The trimaran concept has also been considered for modern warships. The RV Triton was commissioned by British defense contractor QinetiQ in 2000. In October 2005, the United States Navy commissioned for evaluation the construction of a General Dynamics Littoral Combat Ship (LCS) trimaran designed and built by Austal.^[3]

Multihull component terms

There are three terms that describe the components of modern multihulls. The term vaka, like the related terms aka and ama, come from the Malay and Micronesian language group terms for parts of the outrigger canoe, and vaka can be roughly translated as canoe or main hull.^[4]

• Aka^[4] - The aka of a multihull sailboat is a member of the framework that connects the hull to the ama(s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans.
• Ama^[4] - The term ama comes from the proa. The vaka is the main hull, the ama is the outrigger, and the aka^[4] or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimarans.
• Vaka^[4] - A proa consists of a vaka, the main canoe-like hull; an ama, the outrigger; and akas, the poles connecting the ama to the vaka.

Catamarans and trimarans share the same terminology, with a vaka, ama, and aka.^[5]

Semantically, the catamaran is a pair of Vaka held together by Aka, whereas the trimaran is a central Vaka, with Ama on each side, attached by Aka.

The above section reflects American usage. In the UK the main hull of a trimaran is called simply the main hull or centre hull. The side hulls are floats. The structures between the main hull and the floats are called the wings and the structural portions thereof are beams. In cruising trimarans the wings are solid and cabin accommodation extends over them, while in racing trimarans accommodation is limited to the main hull and the wings are open sheets of netting.

Comparison to Monohulls

Two types of trimaran exist: the regular trimaran and the open trimaran, which features a trampoline between the hulls instead of plating.

Trimarans have a number of advantages over comparable monohulls (conventional, single-hulled sailboats). Given two boats of the same length, the trimaran has a shallower draft, a wider beam, less hull area, and is able to fly more sail area. In addition, because of the wide beam, trimarans do not need the weighted keel required in monohulls, this often results in an unsinkable design. As a result of the wide beam, the trimaran offers much better straight-line performance than a monohull, is able to sail in shallower water, and maintains its stability in stronger winds. However, its wider beam requires more space to maneuver, so tacking and gybing can be trickier in confined areas and the narrower hulls provide less living space than an equivalently-sized monohull.

As the righting moment (the force that resists the opposite torque of the wind on the sails) is produced by a float on either side called an ama and not a heavy protruding keel, trimarans are lighter and faster than a monohull of equivalent length. A lightweight retractable keel or foil, referred to as a centerboard or Daggerboard is often employed to resist lateral movement, making many models easily beachable. Most trimarans are difficult to flip sideways given a reasonable degree of caution, however, trimarans can reach speeds so great in high winds that they can plow into the back of a wave and flip end-over-end (Pitchpole). This hazard is especially dangerous for a multihull that is using a spinnakar in high winds and large seas. To avoid this unfortunate scenario trimaran sailors are advised to reduce sail and to always have all sails easily released. The use of trampolines with a large weave, to allow water to easily pass through, and the deployment of parachute anchors drogues and sea anchors whenever appropriate should reduce the risk to an acceptable degree.

The father of the modern sailing trimaran is Victor Tchetchet, a Russian émigré and a strong proponent of multihull sailing. Mr. Tchetchet, who was a fighter pilot during the First World War in the Czar’s Air Force, lived in Great Neck, New York from the 1940’s until his death. He built two trimarans while living in the US, Eggnog 1 and 2. Both boats were made of marine plywood and were about 24 feet long. Mr. Tchetchet is credited with coining the name trimaran. Aside from boat design Mr. Tchetchet earned his living as a landscape and portrait painter. About the same time, Arthur Piver was also building trimarans in the USA and created many early plywood designs to which amateurs built their boats. Many successfully crossed oceans despite being relatively heavy and inferior compared to those of more modern design. The homebuilt cruiser movement survived his death in 1968, with designers Jim Brown, John Marples, Jay Kantola, Chris White, Norman Cross and Richard Newick bringing the trimaran cruiser to new levels of performance and safety.

Folding Trimarans

Several manufacturers build trimarans in which the floats can be folded near to the main hull. This allow them to be trailerable and/or to fit in a normal monohull space in a marina. At least 5 technologies are in use:

• Trimax trimarans use a hightech folding mechanism ^[6]
• Astusboats use telescopic tubes to connect the floats to the main hull.
• Farrier Marine use a vertical folding mechanism ^[7], first used on the Trailertri and subsequently on most of his designs. All Farrier designed boats are known as Fboats (F22, F24, F27 etc).
• Whisper also uses a vertical folding mechanism ^[8]
• Corsair Marine uses a vertical articulation. This system was designed by Ian Farrier and first used by corsair on the "sailing hall of fame" design the F27. All Corsair boats post Farrier designs are known as "Cboats" (C24,C28 etc)
• Dragonfly Trimarans use a nearly horizontal articulation called SwingWing ^[9]. The slightly angle makes the floats fold into the narrower, lower part of the central hull and also increases stability when in the folded position. A similar horizontal articulation design is also used in the Seaon 96CRB. This kind of system was first used in Ocean Bird trimarans designed by John Westell and built by Honnor Marine Ltd of Totnes^[10].
• Telstar 28 uses a unique horizontal folding design along with a simple mast raising system to facilitate trailer sailing. It can be powered easily with the amas folded in or extended.^[11]

Safety

Advantages

Although it is possible for a trimaran to capsize, this is less frequent than with monohull boats because of the greater resistance to rolling that the amas offer. Most trimaran designs are considered nearly unsinkable because even when filled with water, the flotation of one ama is enough to keep the entire vessel afloat. Because of their stability and safety, special trimarans such as the Challenger, have become popular with sailors who have restricted mobility.

The greater speed compared to monohulls can also become important for safety when weather conditions are bad or threaten to deteriorate because the boat can leave the area of danger faster.

Potential buyers of trimarans should look for one that is designed with amas with multiple sealed partitions, controls that all run to the cockpit, a collision bulkhead, partial or full cockpit coverings or windshields, and drain holes in the cockpit that can adequately drain the cockpit quickly, among other things.

Disadvantages

Trimarans capsizes are more likely to be of the pitch-pole type than a roll to one side due to their higher sideways stability and speeds. Capsized trimarans are harder to turn upright than monohull boats. A capsized trimaran should not be righted by sideways rotation as this usually causes heavy damage of the mast and rigging. Harnesses pulling on the stern toward the bow, or from the bow toward the stern of capsized trimarans have been shown to be able to successfully turn them end-over-end. Several design features reduce the chance of pitch-pole capsize. These include having wing nets with an open weave designed to reduce windage and decks and nets that shed water easily. The best way to avoid capsize is to reduce the efficiency of the sails in heavy weather conditions.

In their early days, multihulls including trimarans ran a greater risk of material damage than monohulls. For ocean-going trimarans, even some trimaran sailors still considered this to be true.

Trimarans at anchor or mooring may follow the wind due to their light weight and shallow draft while monohulls usually follow the tides. This can cause collisions if the trimaran is close to another vessel and the swing circles overlap. A bridle to the anchor line may assist in reducing this swing.

World Record

Francis Joyon holds the new world record for solo circumnavigation of the world, set on January 20, 2008. The 51-year-old Frenchman circled the planet alone in 57 days, 13 hours, 34 minutes, 6 seconds in a trimaran. He beat British sailor Ellen MacArthur's record set in February 2005 for which she spent just over 71 days at sea.

The French sailor Olivier de Kersauson is the only one that has won the Jules Verne Trophy with a trimaran.

In naval ships

Littoral combat ships built by General Dynamics at Bath Iron Works will be of a trimaran design. The USS Independence (LCS-2) is the first of these ships. Littoral combat ships built by Lockheed will be of a monohull design.

Image gallery sailing trimarans

"Spirit of Titan" a trimaran, type open ORMA 60, built with hull in carbon fiber, sails in kevlar and other parts in titan in order to minimize the weight. Photo: Round Lidingö Race, May 2009.

"Nokia", a 60 ft long trimaran, type open ORMA 60 in Sandhamn before the Round Gotland Race. Photo: July 2005.

Foldable trimaran with the floats in extended position.

Image gallery engine driven trimarans

Rear view of the USS Independence (LCS-2) at the Austal USA shipyards along the Mobile River in Mobile, Alabama, showing Evolved SeaRAM on hanger roof.

See also

• Catamaran
• Multihull
• RV Triton - A large powered trimaran vessel
• Sailing
• Solar energy
• Arthur Piver

Notes

SmallTrimarans.com

External links

• Trimax Trimarans the Netherlands

References

• "Handbook of offshore cruising: The Dream and Reality of Modern Ocean Cruising". http://books.google.ch/books?id=NB4uFQuUlnEC&pg=PA37&dq=catamaran+cruising+offshore&hl=en&sig=JappWYho-lc6EFs5b-0rkZqO6HM#PPA36,M1. 
• "Aero-Hydrodynamics of Sailing". Tiller Pub. http://books.google.ch/books?id=KYUDAAAACAAJ&dq=Aero-hydrodynamics+of+Sailing&lr=lang_nl%7Clang_en&hl=en.