Disadvantages-- In serious wind and seas, a monohull sailor can, if absolutely exhausted and no longer able to steer, strike all sail, lock all hatches, and go below to wait it out and hope for the best. A well-found boat will most likely allow this.
The boat will roll around like a cork, and even if it rolls 360 degrees it should be ok, as long as the mast doesn't break off and put a hole in the boat. A Multihull in huge seas, however, must always have a helmsman, or some other way to keep the boat pointed into the waves. Without this, the boat will end up in the wave troughs, with the waves beam on; this is an invitation to capsize. Knowing this, the ocean going sailor should be prepared with a parachute sea anchor and with attachment points for it on the boat that are absolutely bombproof. Properly deployed, a parachute anchor will allow a multihull to ride out a hurricane in near comfort, as it keeps the bows pointed into the wind and waves and with several hundred feet of line led out to the sea anchor, there is no jerking or lunging on the line. Once the sea anchor is properly set, the crew can go below and safely wait out the storm. This assumes that there are no dangers, such as a landmass or reef systems, lying in wait downwind. Plenty of sea room is needed for these manuevers.
Marinas-- Finding space in a marina for a multihull is not nearly as easy as it is for a monohull. They require either an end space or a double berth, which will likely cost more than a single.
Weight constraints -- Since a multihull sits on the water instead of in it, unlike a keel boat, the payload, or weight carrying capacity of the boat, can not safely be exceeded. A catamaran, with essentially two full boats in the water, can carry more weight than a trimaran of the same length, which consists of one full hull and two floats. A 35 foot monohull can carry much more weight in stores and equipment than a 35 foot trimaran, and this is a consideration when provisioning a boat for cruising. The cruiser in a small multihull may find himself reprovisioning along the way more often than the cruiser in a small monohull.
Trailerability-- Large multihulls cannot be shipped over the road, due to their wide beam. Only some of the smaller, folding designs will allow trailering.
Haulouts also can be more complicated for multihulls. There are yards that have travelifts wide enough for them, or cranes to lift them, or railways to pull them out of the water on tracks, but these yards are fewer and farther between than those that can't handle the extra wide beam.
Conclusions -- It seems that outside of a couple of minor inconveniences, a multihull is the only boat that makes any sense. If this is the case, why doesn't everyone have one? There are a couple of reasons. One is the unfortunate reputation they earned early on in their evolution. The other is the expense involved in achieving ownership of a quality cat or tri. These boats are expensive to build, whether as one offs or as production models. With a trimaran, 3 hulls (amas) and crossarms (akas) to connect them all together are needed. For production this requires expensive tooling up for a company to invest in even before they ever get a boat on line. There are also a lot more materials needed to build two or three hulls than are needed for the one finished hull of a keel boat.
Other than a production model the buyer has the option of having one custom built by a reputable yard or of building it himself. Neither of these options is cheap, fast, or easy.
There are used multihulls on the market, and there are a lot of good ones out there. There are also a lot of not so good ones. It's critical to hire an experienced multihull surveyor to be assured that the boat was built and maintained properly and is sound.
Rules of the Road...Who has the Right of Way?
The Right of Way rules do not technically come into effect between boats until there is the possibility of collision. Sailboats should never get so close to each other so that a risk of collision exists. vessels should pass portside to portside and as far to starboard as water depth permits.
Sailing Theory, Sailing Terms and Weather
The sum of all wind pressure on the sail iscalled wind force. The center of that force, which is above thewater, is called the center of effort (CE). The center of theforce below the surface of the water is calledthe center oflateral resistance (CLR). This is the point where all the boat'sresistance to sideways pressure is concentrated. A boat performsbest when the two forces are in balance. This is when they arepositioned one over the other in a vertical line through theboat's sail and hull. Your job as a sailor is to keep these twoforces in proper balance so that your boat will sail correctly.You keep the boat balanced by shifting your weight and adjustingyour sail.
