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A multihull is a ship or boat with more than one hull. The additional hulls provide stability, typically to hold the vessel upright against the sideways force of the wind on the sails. This is in contrast to monohulls which typically use a keel and/or ballast for this purpose, especially on larger sailboats.

Multihulls include: proas, which have two differently sized hulls; catamarans, which have two similar hulls; and trimarans, which have a larger hull in the center and two smaller ones on either side. Multihull sailboats are typically much wider than the equivalent monohull, which allows them to carry no ballast, so they are typically faster than monohulls under equivalent conditions (see Nathanael Herreshoff's "Amarylis", also 1988 America's Cup). It also means that multihulls are less prone to sink than monohulls when their hulls are compromised. There are also multihull powerboats, both for racing and transportation.

Contents 1 Advantage of multihulls 2 Disadvantage of Multihulls 3 Popularity 4 Popular multihulls 5 Trivia 6 See also 7 External links

Multihulls are substantially faster than monohulls, because the absence of ballast reduces their weight and the amount of drag through the water (see hull speed) considerably and because they rise out of the water more easily, which also reduces drag (see planing). The waterline to width ratio is larger, allowing the thinner hulls to be driven through the water at higher speeds, as each works somewhat independently of the other(s).

The width of a multihull vessel is often an issue, especially when docking. They are also more expensive to produce than a monohull of the same length.

It is a common concern that in the open ocean, multihull craft are unsafe in a heavy storm. If a storm or wave capsizes a small monohull, it may recover when the weight of the ballast in the keel rights the boat, if it does not broach and sink before it recovers. Multihulls can capsize but they rarely sink; instead they float upside-down. Many rescued crews (in races) have reported that they were unable to dismount the deck-mounted liferaft or emergency radio from the mass of broken, submerged rigging under the capsized craft.

Another risk in a multihull is the "pitch pole"; where the bow of the boat buries itself into a wave and the stern flips over putting the boat into a forward somersault; this tends to be more common in smaller racing multihulls, which carry large sails in relation to their weight. This rarely effects monohulls because they carry more ballast which prevents the tendency to flip, and helps them power through waves.

• Proponents argue that no careful captain ever finds himself in capsizing conditions. Most crews that have capsized in the open ocean found it an extremely traumatic event no matter what type of boat they sailed.

• Proponents also argue that capsize is only one of many types of catastrophe that can befall yachts at sea. In other types (for example hull compromise by hitting submerged debris) multihulls are substantially safer than monohulls because they don't carry ballast and can therefore float even when severely damaged.

It has been said that, while it is true that a catamaran is ultimately stable floating upside down, a traditional keel boat is ultimately stable resting on the bottom of the ocean.

Multihulls are quite popular for racing, especially in Europe and Australia, and are somewhat popular for cruising in the Caribbean. They're not seen very often in the United States, although they're gradually getting more popular. Until the 1980s most multihull sailboats (except for beach cats) were built either by their owners or by boatbuilders on a semi-custom basis. Since then several companies have been successful selling mass-produced (by boat industry standards) boats.

There are many types of multihulls in different categories. Among the small sailing catamarans, also called beach catamarans, the most recognized racing classes are the Hobie Cat 16, Formula 18 cats, A-cats and the Olympic multihull called Tornado.

Larger boats include Corsair Marine (mid-sized trimarans), and Privilege (large, luxurious catamarans). The largest manufacturer of large multihulls is Fountaine Pajot in France. But also the much larger French trimarans of the ORMA racing cirquit and round the world record attempts are included in this.

In the powerboat part of the multihull spectrum we find a range of boats from small single pilot Formula 1 power boat series to the large multi-engined or even gas turbined power boats that are used in the off-shore powerboat racing series and that are piloted by 2 to 4 pilots.

The catamaran is also known as a multihull and also comes in a 'power' flavor with no sailing apparatus. In fact, pure power catamarans are now becoming a common sight in international charter fleets in the Caribbean and Mediterranean. Further, a new breed of catamarans has now started to take shape in the form of the mega or super catamaran. This definition is reserved for those catamarans over 60 feet in length. It usually takes one year to build these huge vessels and often a large amount of customization takes place at the request of the owner who commissions the vessel.

• Catamaran
• Trimaran
• Monocat
• Sailing
• Round Texel
• International C-Class Catamaran Championship
• International Catamaran Challenge Trophy

• http://www.catamaran.co.uk/main.htm The UK Catamaran Racing Association
• http://www.catsailor.com/forums/ubbthreads.php Forum page for small sailing catamarans (beach cats)
• http://www.mycq.org.au Australian multihull club
• http://www.mycv.asn.au Australian multihull yacht club Blog
• http://multihullboatbuilder.org Multihull Boatbuilding Information / Community
• http://www.multihull-maven.com Articles and news on multihulls, profiles of boats, designers, yards, etc.
• http://www.sailing.org International Sailing Federation
• http://wingo.com/proa Proa design (in development stage)
• http://ducky.com.ua/index_eng.htm Inflatable modular sailing catamarans - Ducky

Types of sailing vessels and rigs

Barque | Barquentine | Bermuda rig | Bilander | Brig | Brigantine | Caravel | Carrack | Catamaran | Catboat | Clipper | Dutch Clipper | Cog | Corvette | Cutter | Dhow | Fifie | Fluyt | Fore & Aft Rig | Frigate | Full Rigged Ship | Gaff Rig | Galiot | Galleon | Gunter Rig | Hermaphrodite Brig | Jackass-barque | Junk | Ketch | Longship | Mersey Flat | Multihull | Nao | Norfolk Wherry | Pink | Pocket Cruiser | Polacca | Pram | Proa | Sailing hydrofoil | Schooner | Ship of the Line | Sloop | Smack | Snow | Square Rig | Tall Ship | Thames Sailing Barge | Trimaran | Vinta | Wherry | Windjammer | Windsurfer | Xebec | Yacht | Yawl