Multihull

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The relationship between monohulls & multihulls

A multihull is a boat or ship with more than one hull, whereas a vessel with a single hull is a monohull. The most common multihulls are catamarans (with two hulls), and trimarans (with three hulls). There are other types, with four or more hulls, but such examples are very rare and tend to be specialised for particular functions.<ref>Dubrovsky, V (2004) Ships with Outriggers, Backbone Publishing Co, Template:ISBN</ref>

Multihull history

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A Polynesian catamaran

Single-outrigger boats, double-canoes (catamarans), and double-outrigger boats (trimarans) of the Austronesian peoples are the direct antecedents of modern multihull vessels. They were developed during the Austronesian Expansion (c. 3000 to 1500 BC) which allowed Austronesians to colonize maritime Southeast Asia, Micronesia, Island Melanesia, Madagascar, and Polynesia. These Austronesian vessels are still widely used today by traditional fishermen in Austronesian regions in maritime Southeast Asia, Oceania and Madagascar; as well as areas they were introduced to by Austronesians in ancient times like in the East African coast and in South Asia.<ref name="Mahdi1999">Template:Cite bookTemplate:Dead link</ref><ref name="Doran1981">Template:Cite book</ref><ref name="Beheim">Template:Cite journal</ref><ref name="Hornell1932">Template:Cite journal</ref><ref name="Doran1974">Template:Cite journal</ref>

Greek sources also describe large third-century BC catamarans, one built under the supervision of Archimedes, the Syracusia,<ref name="Casson">Template:Cite book</ref> and another reportedly built by Ptolemy IV Philopator of Egypt, the Tessarakonteres.<ref name="athenaeus">Template:Cite book</ref><ref name="athenaeus2">Template:Cite book</ref>

Modern developers

Modern pioneers of multihull design include James Wharram (UK), Derek Kelsall (UK), Tom Lack (UK), Lock Crowther (Aust), Hedly Nicol (Aust), Malcolm Tennant (NZ), Jim Brown (USA), Arthur Piver (USA), Chris White (US), Ian Farrier (NZ), LOMOcean (NZ), Darren Newton (UK), Jens Quorning (DK) and Dick Newick (USA).

Multihull types

Single-outrigger ("proa")

File:National Museum of Ethnology, Osaka - Single outrigger canoe (model) - Woleai Atoll in Federated States of Micronesia - Collected in 1985.jpg

Model of a wa, a single-outrigger vessel, from Woleai in the National Museum of Ethnology (Japan)

A single-outrigger canoe is a canoe with a slender outrigger ("ama") attached by two or more struts ("akas"). This craft will normally be propelled by paddles. Single-outrigger canoes that use sails are usually inaccurately referred to by the name "proa". While single-outrigger canoes and proas both derive stability from the outrigger, the proa has the greater need of the outrigger to counter the heeling effect of the sail. The outrigger on a proa can either be on the lee or windward side, or in a tacking proa, interchangeable. However, more recently, proas tend to keep the outrigger either to leeward or to wind which means that instead of tacking, a "shunt" is required, whereby the bow becomes the stern, and the stern becomes the bow.

Catamaran (twin-hull)

Template:Main A catamaran is a vessel with twin hulls. Commercial catamarans began in 17th century England. Separate attempts at steam-powered catamarans were carried out by the middle of the 20th century. However, success required better materials and more developed hydrodynamic technologies. During the second half of the 20th century catamaran designs flourished. Catamaran configurations are used for racing, sailing, tourist and fishing boats.

The hulls of a catamaran are typically connected by a bridgedeck, although some simpler cruising catamarans<ref>Such as some Wharram designs</ref> simply have a trampoline stretched between the crossbeams (or "akas").<ref name="dubrovsky2001">Dubrovsky, V, Laykhovitsky, A (2001) Multi Hull Ships. Backbone Publishing Co. Template:ISBN</ref> Small beachable catamarans, such as the Hobie Cat, also have only a trampoline between the hulls.

Catamarans derive stability from the distance between the hulls—transverse clearance—the greater this distance, the greater the stability.<ref name=Garrett>Template:Cite book</ref> Typically, catamaran hulls are slim, although they may flare above the waterline to give reserve buoyancy.<ref>As in all the Catalac designs</ref> The vertical clearance between the design waterplane and the bottom of the bridge deck determines the likelihood of contact with waves. Increased vertical clearance diminishes such contact and increases seaworthiness, within limits.<ref>Template:CitationTemplate:Dead link</ref>

The twin-hull (catamaran) design is effective in enhancing the stability of very small, lightweight and narrow personal boats designed for paddling and powering with portable outboard motors. The 100 lbs (45 kg), 38 inches (96 cm) wide Wavewalk S4 Microskiff catamaran is sufficiently stable to allow for three adult anglers to stand in it and fish in full confidence, and it allows for three adults to stand in it and paddle in full confidence.

Trimaran (double-outrigger)

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A 60' trimaran with high aspect fractional Bermuda rig

A trimaran (or double-outrigger) is a vessel with two outrigger floats attached on either side of a main hull by a crossbeam, wing, or other form of superstructure. They are derived from traditional double-outrigger vessels of maritime Southeast Asia.<ref name="Mahdi1999"/><ref name="Doran1981"/><ref name="Beheim"/> Despite not being traditionally Polynesian,<ref name="Hornell1932"/><ref name="Doran1974"/> western trimarans use traditional Polynesian terms for the hull (vaka), the floats (ama), and connectors (aka).<ref>Template:Cite book</ref> The word trimaran is a portmanteau of tri and (cata)maran,<ref>Collins English Dictionary – 2007 – Harper Collins – Template:ISBN</ref> a term that is thought to have been coined by Victor Tchetchet, a pioneering modern multihull designer, born in Ukraine (at that time part of the Russian Empire).<ref name="mm2">Template:Cite web</ref>

Some trimaran configurations use the outlying hulls to enhance stability and allow for shallow draft, examples include the experimental ship RV Triton<ref>Template:Cite web</ref> and the Independence class of littoral combat ships (US).<ref>Template:Cite web</ref>

Four and five hulls

Some multihulls with four (quadrimaran) or five (pentamaran) hulls have been proposed; few have been built.<ref name="qf">Template:Cite journal</ref> In 2018 a Swiss entrepreneur sought funding<ref>Template:Cite web</ref> to build a sail-driven quadrimaran called Manta that would use solar power to scoop plastic from the ocean.<ref>Template:Cite web</ref> Manta was still under development as of the end of 2023.<ref>Template:Cite web</ref> A French manufacturer, Tera-4, produces motor quadrimarans which use aerodynamic lift between the four hulls to promote planing and reduce power consumption.<ref>Template:Cite web</ref>

Design concepts for vessels with two pair of outriggers have been referred to as pentamarans. The design concept comprises a narrow, long hull that cuts through waves. The outriggers then provide the stability that such a narrow hull needs. While the aft sponsons act as trimaran sponsons do, the front sponsons do not touch the water normally; only if the ship rolls to one side do they provide added buoyancy to correct the roll.<ref>Template:Cite web</ref><ref>Template:Cite news</ref> BMT Group, a shipbuilding and engineering company in the UK, has proposed a fast cargo ship and a yacht using this kind of hull.<ref>Template:Cite web</ref><ref>Template:Cite news</ref>

SWATH multihulls

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A narrow waterline distinguishes a SWATH ship from a conventional catamaran

Multihull designs may have hull beams that are slimmer at the water surface ("waterplane") than underwater. This arrangement allows good wave-piercing, while keeping a buoyant hydrodynamic hull beneath the waterplane. In a catamaran configuration this is called a small waterplane area twin hull, or SWATH.<ref>Template:Cite book</ref> While SWATHs are stable in rough seas, they have the drawbacks, compared with other catamarans, of having a deeper draft, being more sensitive to loading, and requiring more power because of their higher underwater surface areas.<ref>Template:Cite web</ref> Triple-hull configurations of small waterplane area craft had been studied, but not built, as of 2008.<ref>Template:Cite journal</ref>

Performance

Each hull of a multihull vessel can be narrower than that of a monohull with the same displacement<ref>Most ships (excluding hydrofoils and planing hulls) stay afloat by displacing their weight in water. A multihull can divide that displacement between multiple, narrow hulls. A monohull must be deeper, longer, or wider to displace the same amount of water. A single long, deep hull would be unstable and hard to maneuver, so monohulls are almost always wider than the individual hulls of a multihull vessel.</ref> and long, narrow hulls, a multihull typically produces very small bow waves and wakes, a consequence of a favorable Froude number.<ref>The Froude number of any hull is calculated by <math>\mathrm{Fn}_L = \frac{u}{\sqrt{gL}},</math> where Template:Math is the relative flow velocity between the sea and ship, Template:Math is in particular the acceleration due to gravity, and Template:Math is the length of the ship at the water line level, or Template:Math in some notations. It is an important parameter with respect to the ship's drag, or resistance, especially in terms of wave making resistance.</ref><ref>Template:Citation</ref><ref>Template:Cite web</ref> Vessels with beamy hulls (typically monohulls) normally create a large bow wave and wake. Such a vessel is limited by its "hull speed", being unable to "climb over" its bow wave unless it changes from displacement mode to planing mode. Vessels with slim hulls (typically multihulls) will normally create no appreciable bow wave to limit their progress.

In 1978, 101 years after catamarans like Amaryllis were banned from yacht racing<ref name="ym">Template:Cite magazine</ref><ref name="Spirit">Template:Cite web</ref> they returned to the sport. This started with the victory of the trimaran Olympus Photo, skippered by Mike Birch in the first Route du Rhum. Thereafter, no open ocean race was won by a monohull. Winning times dropped by 70%, since 1978. Olympus Photo's 23-day 6 hr 58' 35" success dropped to Gitana 11's 7d 17h 19'6", in 2006. Around 2016 the first large wind driven foil-borne racing catamarans were built. These cats rise onto foils and T-foiled rudders only at higher speeds.Template:Citation needed

Sailing multihulls and workboats

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A catamaran ferry in Salem, Massachusetts

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A French catamaran trawler

The increasing popularity of catamaran since the 1960s is down to the added space, speed, shallow draft, and lack of heeling underway. The stability of a multihull makes sailing much less tiring for the crew, and is particularly suitable for families. Having no need for ballast for stability, multihulls are much lighter than monohull sailboats; but a multihull's fine hull sections mean that one must take care not to overload the vessel. Powerboats catamarans are increasingly used for racing, cruising and as workboats and fishing boats. Speed, the stable working platform, safety, and added space are the prime advantages for power cats.

"The weight of a multihull, of this length, is probably not much more than half the weight of a monohull of the same length and it can be sailed with less crew effort."<ref name=OffshoreHandbook>Template:Cite book</ref>

Racing catamarans and trimarans are popular in France, New Zealand and Australia. Cruising cats are commonest in the Caribbean and Mediterranean (where they form the bulk of the charter business) and Australia. Multihulls are less common in the US, perhaps because their increased beam require wider dock/slips. Smaller multihulls may be collapsible and trailerable, and thus suitable for daybooks and racers. Until the 1960s most multihull sailboats (except for beach cats) were built either by their owners or by boat builders; since then companies have been selling mass-produced boats, of which there are more than 150 models.<ref>"Sailor's Multihull Guide" - 3rd edition</ref>

References and Bibliography

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• Harvey, Derek, Multihulls for Cruising and Racing, Adlard Coles, London 1990, Template:ISBN

External links

• The Multihull Offshore Cruising & Racing Association
• The UK Catamaran Racing Association
• The Multihull Yacht Club of Queensland (Australia) Template:Webarchive
• Multihull Boatbuilding Information / Community
• Articles and news on multihulls, profiles of boats, designers, yards, etc. Template:Webarchive
• Multihulls designer & builder Template:Webarchive
• International Sailing Federation Template:Webarchive
• The multihulls reference magazine
• The multihulls reference magazine (Australia) Template:Webarchive