One or several hulls?

Almost all boats in our part of the world have traditionally only had one hull. Elsewhere in the world, multihulls have been common, particularly where wind has been the most important method for propulsion.

The modern multihull has been developed over the last fifty years, and in fact Norway is a country that has very successfully used multihulls for both goods and passenger transportation along the coast, and for car and passenger transportation between Norway and Denmark. With no exception these boats have been catamarans; i.e. they have two identical hulls. They are well known for being both fast and seaworthy.

Single- and multihull sailboats

A sailboat with one hull uses weight for balancing  - a small boat uses the weight of the crew, and a larger boat uses the weight of its keel. Without weight balancing the boat will heel, and might even capsize in strong wind. In order to sail fast the weight will either have to be far out (e.g. crew in trapeze) or deep down (e.g. deep keel), or a combination of the two.

The trimaran

The trimaran - a boat with three hulls - is the fastest of all sailboats. It has one mail hull, and floats (actually small hulls) on either side of the main hull, and is often almost as wide as it is long. Modern trimarans often have large volume floats, similar in length to the main hull. An inverted bow is also a common sight for trimarans these days; such a bow will pierce the waves rather than lift above them, but will also make the boat wetter.

Most trimarans have a swing centreboard or a retractable daggerboard in the main hull. The rudder may be attached to the main hull, or there could be one rudder in each float.  Some trimarans also have foils for stabilization, lift and added speed.

Weight, beam, length and sail area arguably are the main factors for good performance. See here for a comparison of several small trimarans, where I have used a ratio between weight and sail area to indicate performance.

Read about the background for my interest in multihulls here. Note that this is a blog posting in Norwegian.

Folding and demounting

A trimaran is almost as wide as it is long; hence it takes a lot of space under transport, afloat and at winter storage.  Larger trimarans have fixed floats (e.g. Neel). Some trimarans also have floats that can be demounted during transport or at winter storage (Libertist 853). Such boats are often at a mooring or alongside a jetty, because many marinas (at least in Norway) do not offer such wide berths (or it costs too much).

The New Zealand naval architect Ian Farrier was the first to develop a practical  method for folding a trimaran. A trimaran with floats that can be folded toward the main hull without demounting is therefore just as practical to own as a boat with one hull. Since such a boat does not have a fixed, heavy keel, it is easy to store on an ordinary boat trailer. Many trimaran manufacturers have also designed a system for raising and lowering the mast by means of onboard equipment and winches.

There are several methods for folding:

  • ladder-frame folding; the floats swing toward and partly underneath the main hull  (Farrier, Corsair and others)

  • sliding tube folding; the floats are mounted on telescopic tubes that are pushed toward the main hull (Astus)

  • swing arm folding; the floats swing rearward and  toward the main hull (Dragonfly, Libertist, Tricat, W19)

  • hinge folding; the floats are mounted on hinges, and swing up, resting on top of the main hull (W17, Discovery 21)

All these methods have their advantages and drawbacks. Ladder-frame folding is most compact, not making the boat longer, but the floats are exposed to growth when they are folded toward and slightly underneath the main hull.  Sliding tube folding can be a problem if sand enters the telescopic tubes; these tubes also take up space. Swing arm folding makes the boat longer when folded; this method also adds weight. Hinge folding is most suitable for small boats with a flat deck, and cannot be used when the boat is afloat.

Mike Waters´ Small Trimaran Sailing Tips

Read Mike Waters excellent small trimaran sailing techniques handbook online.

(Copyright © 2010-2020 mike waters)

Why a trimaran?

What is wrong with the monohull sailboat? Certainly not looks - a well designed monohull is, in my opinion, better looking than a trimaran, with its beams, different size hulls and trampolines, and the many "wedding cake" catamarans one sees these days are also not beautiful. So what is the problem with the monohull sailboat?
  • monohull sailboats with fixed keel and ballast can sink
  • most monohull sailboats are not fast; 6-8 knots is typical speed
  • the monohull sailboat is comfortable at harbour, and partly when motoring, but it most often heels under sail; maybe to the enjoyment of the avid sailor, but what fun is it to have boat with all comforts, when you have to brace yourself most of the time; would you buy a comfortable car that heels heavily to one side or the other when driven? 
Trimaran Advantages:

  • little or no heeling; thus more comfort
  • very safe, because the boat cannot sink
  • high speed, fast acceleration, and thus longer range (very important for daysailing)
  • sails well also with little wind (so less motoring)
  • large deck space
  • low weight
  • raising centreboard or daggerboard gives low draft

Trimaran Disadvantages:

  • little cabin space, because the main hull is long and narrow

  • three hulls, and equipment demanding high strength in both hull and rig (due to high acceleration) make for high building costs

  • very limited market for used trimarans (at least true in Norway)

  • non folding trimarans are expensive in a marina

  • high windage of main hull and rig, and low weight, makes the boat decelerate as easy as it accelerates

What does a trimaran cost?

Typically a new 20-30 foot trimaran with a cabin will cost between € 50,000 to 200,000. In Norway very few boats are for sale. With import of a new or second hand boat to Norway, 25 % VAT has to be added. In general, prices for second hand boats are higher abroad than in Norway.

An open trimaran below 20 ft costs between € 20-50,000.

Libertist 853 with fixed floats and foils


Small Trimaran Design

Website with loads of useful information about small trimarans. Mike Waters has many decades of practical designing and sailing experience. The site introduces in detail his two well designed trimarans - the W17 and W22.


Jim Brown´s website chronicling the development of the modern trimaran

Erik Lerouge Yacht Design

Erik Lerouge´s website - well known French multihull naval architect

Small Trimarans

Website with information about small trimarans in general