Trimaran

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 Catri, Farrier, and Corsair folding trimarans and Quorning and Elan Series swing wing trimarans. Many sailboat designers have also designed demountable trimarans that are able to be trailered.

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.^[1] 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.^[2]

Construction

2 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. As a result, 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 makes it a little more cumbersome to maneuver, so tacking and gybing can be trickier, 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, referred to as a centerboard is often employed to resist lateral movement, making many models easily beachable. Most trimarans are nearly impossible to flip sideways given a reasonable degree of caution, however, trimarans can reach speeds so great in a storm that they can plow into a wave and flip end-over-end. This hazard is especially dangerous for a multihull because of their wide beam. The front of the boat, often covered by trampoline, acts as a giant paddle rather than a narrow monohull would. To avoid this unfortunate scenario trimaran sailors are advised to use trampolines with a large weave and employ parachute drogues and sea anchors whenever appropriate.

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.

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, trimarans such as the Challenger class have become popular with sailors who have restricted mobility.

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

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.