Monohull yachts are typically fitted with a fixed or adjustable keel below the waterline to counterbalance the overturning force of wind on the vessel's sails. By contrast, multihull yachts (a catamaran is an example of this type of vessel) use two or more hulls widely separated from each other to provide a stable base that resists overturning.
A keel is a large beam around which the hull of a ship is built. The keel runs in the middle of the ship, from the bow to the stern, and serves as the foundation of the structure, providing the major source of structural strength of the hull. The word keel is also sometimes used to refer to a rigid, relatively flat piece of material anchored to the lowest part of the hull and used to give the ship greater directional control and stability. Large keels are common in heavy monohull yachts, where they act as foils, using the forward motion of the boat to generate lift to counter the lateral force from the sails. Keels are different from centerboards in that keels are often fixed (though some are retractable) and are often made of heavy materials to provide ballast to stabilize the boat.
Although the principles of sailing are the same for both catamarans and monohulls, there are some differences. For example:
Catamarans can be harder to tack (turn through the wind), than heavy monohull yachts.
Because catamarans are lighter in proportion to their sail size, they have less momentum to carry them through the turn when they are head to wind.
Heavy monohull yachts have a lower average speed.
All boats sail faster when travelling in certain directions relative to the wind the best speeds typically being achieved when heading away from the wind at about 135 degrees. This effect is much more noticeable with catamarans, even to the extent that it can be more efficient to jibe ('tack' downwind) in zig zags, rather than heading directly away from the wind as a monohull would.
Gybing is another maneuver that needs to be treated in the same way as tacking . When gybing you are changing tacks and setting up your sails on the other side of the boat. Whatever size of boat you are sailing it is important to understand that the rate of the turn , the sails transferring sides and the crews mechanics must have a sequential order, and be timed correctly to achieve the elusive perfect gybe. The perfect gybe will vary both in mechanics and aesthetics from boat to boat. Smaller keelboats can change direction rapidly and have sails that can be trimmed and rotated quickly, larger heavy monohull yachts require far more manpower, time and distance to gybe.
Catamarans are less likely to capsize in the classic 'beam-wise' manner but often have a tendency to 'pole-axe' (or 'pitchpole') instead - where the leeward (downwind) bow sinks into the water and the boat 'trips' over forward, leading to a capsize.
Teaching for new sailors is usually carried out in monohulls as they are thought easier to learn to sail, a mixture of all the differences mentioned probably contributes to this.
Many people today don't like the constant rolling and movement of heavy monohull yachts while under way or sitting at their anchorage. Besides, a catamaran provides much more room, from as little as 24' wide to 28' wide on 50' The displacement hull design for power catamarans, allows for economy cruising at 16 to 18 knots and top speeds of 23 knots. These speeds and economy are not possible in conventional monohull or traditional monohull trawler.
A luxury sailboat can offer the ultimate in floating luxury. These self-contained worlds are built and run as small elegant hotels. At the top end of the market, the larger yachts have a choice of saloon, bar and relaxation area both inside and on the various deck levels. The accommodation is spacious and luxuriously decorated with the finest fabrics and often, exquisite pieces of art, while the bathrooms are finished with acres of marble.