Points of sail
The points of sail are the most important parts of sail theory to remember. The wind, irons, or no go zone, is about 45° either side of the true wind, for a racing hull and sail plan optimized for upwind work. More commonly and on cruising sailplans, the best angle achievable upwind is 50° to 55° to the true wind. A boat cannot sail directly into the wind; attempting to do so is called luffing. There are 5 main points of sail. In order from the edge of the no go zone to directly downwind they are:
- close haul (22° to the apparent wind)
- close reach (half way between close hauled and a beam reach)
- beam reach (90° to the apparent wind)
- broad reach (22.5° away from directly downwind sailing)
- running (directly downwind)
The sail trim (and, on smaller boats, centre board/dagger board position) on a boat is relative to the point of sail one is on: on a beam reach sails are half way out, on a run sails are all the way out, and close hauled sails are pulled in very tightly. A large proportion of the skill of sailing is in trimming the sails correctly for direction and strength of the wind.
Sailing hulls and hull shapes
Sailing boats with one hull are "monohulls", those with two are "catamarans", those with three are "trimarans". A boat is turned by a rudder, which itself is controlled by a tiller or a wheel, while at the same time adjusting the sheeting angle of the sails. Smaller sailing boats often have a stabilising, raisable, underwater fin called a centreboard (or daggerboard); larger sailing boats have a fixed (or sometimes canting) keel. As a general rule, the former are called dinghies, the latter keelboats. However, up until the adoption of the Racing Rules of Sailing, any vessel racing under sail was considered a yacht, be it a multi-masted ship-rigged vessel (such as a sailing frigate), a sailboard (more commonly referred to as a windsurfer) or remote-controlled boat, or anything in between. (see Dinghy sailing)
Multihulls use flotation and/or weight positioned away from the centre line of the sailboat to counter the force of the wind. This is in contrast to heavy ballast that can make up to ⅓ of the weight of a monohull sailboat. In the case of a standard catamaran there are two similarly sized and shaped slender hulls connected by beams, which are sometimes overlaid by a deck superstructure. Another catamaran variation is the proa. In the case of trimarans, which have an unballasted centre hull similar to a monohull, two relatively smaller amas are situated parallel to the centre hull to resist the sideways force of the wind. The advantage of multihulled sailboats is that they do not suffer the performance penalty of having to carry heavy ballast, and their relatively lesser draft reduces the amount of drag, caused by friction and inertia, when moving through the water.
Types of sails and layouts
A traditional modern yacht is technically called a "Bermuda sloop" (sometimes a "Bermudan sloop"). A sloop is any boat that has a single mast and a headsail (generally a jib) in addition to the mainsail. The Bermuda designation refers to the fact that the sail, which has its forward edge (the "luff") against the mast (the main sail), is a sail roughly triangular in shape. Additionally, Bermuda sloops only have a single sail behind the mast. Other types of sloops are gaff-rigged sloops and lateen sloops. Gaff-rigged sloops have quadrilateral mainsails with a gaff (a small boom) at their upper edge (the "head" of the sail). Gaff-rigged vessels may also have another sail, called a topsail, above the gaff. Lateen sloops have triangular sails with the upper edge attached to a gaff, and the lower edge attached to the boom, and the boom and gaff are attached to each other via some type of hinge. It is also possible for a sloop to be square rigged (having large square sails like a Napoleonic Wars-era ship of the line). Note that a "sloop of war," in the naval sense, may well have more than one mast, and is not properly a sloop by the modern meaning.
If a boat has two masts, it may be a schooner, a ketch, or a yawl, if it is rigged fore-and-aft on all masts. A schooner may have any number of masts provided the second from the front is the tallest (called the "main mast"). In both a ketch and a yawl, the foremost mast is tallest, and thus the main mast, while the rear mast is shorter, and called the mizzen mast. The difference between a ketch and a yawl is that in a ketch, the mizzen mast is forward of the rudderpost (the axis of rotation for the rudder), while a yawl has its mizzen mast behind the rudderpost. In modern parlance, a brigantine is a vessel whose forward mast is rigged with square sails, while her after mast is rigged fore-and-aft. A brig is a vessel with two masts both rigged square.
As one gets into three or more masts the number of combinations rises and one gets barques, barquentines, and full rigged ships.
A spinnaker is a large, full sail that is only used when sailing off wind either reaching or downwind, to catch the maximum amount of wind.
Types of Sailboats
At present, a great number of sailboat-types may be distinguished. Apart from size, sailboats may be distinguished by hull configuration (monohull, catamaran, trimaran), keel type (full, fin, wing, centerboard etc.), purpose (sport, racing, cruising), number and configuration of masts, and sail plan. Although sailboat terminology has varied across history, many terms now have specific meanings in the context of modern yachting.
Sloop
Today, the most common sailboat is the sloop which features one mast and two sails, a normal mainsail and a foresail. This simple configuration is very efficient for sailing towards the wind. The mainsail is attached to the mast and the boom, which is a spar capable of swinging across the boat, depending on the direction of the wind. Depending on the size and design of the foresail it can be called a jib, genoa, or spinnaker; it is possible but not common for a sloop to carry two foresails from the one forestay at one time (wing on wing). The forestay is a line or cable running from near the top of the mast to a point near the bow. In Bermuda, where a rig design influenced by the Lateen rig appeared on boats and came to be known as the Bermuda rig, a large spinnaker was carried on a spinnaker boom when running down-wind. An example of a typical sloop can be seen on the Islander 36.
Fractional Rig Sloop
On a fractional rig sloop the forestay does not run to the top of the mast, rather it connects at some point below. This allows the top of the mast to be raked aft by increasing the tension of the backstay, while arching the middle of the mast forward. Without great explanation, this gives a performance advantage in some conditions by flattening the sails. The big mainsail provides most of the drive, and the small headsail is easier for a short-handed crew to manage.
Cutters
The cutter is similar to a sloop with a single mast and mainsail, but generally carries the mast further aft to allow for the use of two headsails attached to two forestays, the head stay and the inner stay, which carry the jib and staysail respectively. This is rarely considered a racing configuration; however, it gives versatility to cruising boats, especially in high wind conditions, when a small jib can be flown from the inner stay.
Importantly, the traditional and most accurate definition of a true cutter, however, is not in the number of headsails, but rather that the outermost sails are set on stays that are not strictly structural to the rig itself. This in itself is a function of a much more complicated design set, involving mast placement, mast height, rig, boom length and fore-triangle size.
Catboats
A catboat has a single mast mounted fairly forward and does not carry a head sail (jib etc.). Most modern designs have only one sail, the mainsail; however the traditional catboat could carry multiple sails from the gaff rig. The designer of the Catboat is Brian Husband, master sailor of the early 1940s.
Ketches
Ketches are similar to a sloop, but there is a second shorter mast to the stern of the mainmast, but forward of the rudder post. The second mast is called the mizzen mast and the sail is called the mizzen sail. A ketch can also be cutter-rigged with two headsails.
Schooner
A schooner can have two or more masts, the aftermost mast taller or equal to the height of the forward mast(s), distinguishing this design from a ketch or a yawl. Top sail schooners are rigged to carry a square sail near the top of their foremast, but generally modern schooners are gaff or marconi rigged.
Yawl
A yawl is similar to a ketch, with the mizzen mast shorter than the main mast but the mizzen mast is carried astern of the rudder post. Generally the mizzen on a yawl is smaller than the mizzen on a ketch, and is used more for balance than propulsion.
Dhoni
Dhoni or Doni (Dhivehi: ދޯނި pronounced Dōni) is a multi-purpose sail boat with a motor or lateen sails that is used in the Maldives. It is handcrafted and its use within the multi-island nation has been very important. A dhoni resembles a dhow, a traditional Arab sailing vessel.
Hulls
Traditional sailboats are monohulls, but multi-hull catamarans and trimarans are gaining popularity. Monohull boats generally rely on ballast for stability, and usually are displacement hulls. This stabilizing ballast can, in boats designed for racing, be as much as 50% of the weight of the boat, but is generally around 30%. It creates two problems; one, it gives the monohull tremendous inertia, making it less maneuverable and reducing its acceleration. Secondly, unless it has been built with buoyant foam or air tanks, if a monohull fills with water, it will sink.
- "... 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."
Multihulls rely on the geometry and the broad stance of the multiple hulls for their stability, eschewing any form of ballast. Indeed, multihulls are designed to be as light-weight as possible, yet maintain structural integrity. They are often built with foam-filled flotation chambers and many modern commercial trimarans are rated as unsinkable, meaning that, should every crew compartment be completely filled with water, the hull itself has sufficient buoyancy to remain afloat.
This absence of ballast also results in some very real performance gains in terms of acceleration, top speed, and maneuverability.
- The lack of ballast makes it much easier to get a multihull on plane, reducing its wetted surface area and thus its drag.
- Compared to a monohull, acceleration to top speed is near-instantaneous.
- Reduced overall weight means a reduced draft, with a much reduced underwater profile. This, in turn, results directly in reduced wetted surface area and drag, yielding higher top speeds.
- Without a ballast keel, multihulls can go in shallow waters where monohulls can't.
On the other hand, a well designed ballasted boat can recover from a capsize, even from turning over completely. The Swan 65 Sayula II won the 1973-74 Whitbread Round the World Race after doing a 180 degree capsize in the Southern Ocean. Righting a multihull that has gotten upside down is difficult in any case and impossible without outside help unless the boat is small or carries special equipment for the purpose. Several round the world racing multihulls have been lost after they capsized.
Also, structural integrity is much easier to achieve in a one piece monohull than in a two or three piece multihull whose connecting structure must be substantial and well connected to the hulls.
All these hull types may also be manufactured as, or outfitted with, hydrofoils.
Keel
All vessels have keels, it is the backbone of the hull. In traditional construction it is the structure upon which all else depends. Modern monocoque designs include a virtual keel. Even multihulls have keels. On a sailboat the word Keel is also used to refer to the area that is added to the hull to improve its lateral plane. The lateral plane is what prevents leeway and allows sailing towards the wind. This can be an external piece or a part of the hull.
Most monohulls larger than a dinghy require ballast, depending on the design ballast will be 20 to 50 percent of the displacement. The ballast is often integrated into their keels as large masses of lead or cast iron. This secures the ballast and gets it as low as possible to improve its effectivness. External keels are cast in the shape of the keel. A monohull's keel is made effective by a combination of weight, depth and length.
Most modern monohull boats have fin keels, which are heavy and deep, but short in relation to the hull length. More traditional yachts carried a full keel which is generally half or more of the length of the boat. A recent feature is a winged keel, which is short and shallow, but carries a lot of weight in two "wings" which run sideways from the main part of the keel. Even more recent is the concept of canting keels, designed to move the weight at the bottom of a sailboat to the upwind side, allowing the boat to carry more sails.
Multihulls, on the other hand, have minimal need for such ballast, as they depend on the geometry of their design, the wide base of their multiple hulls, for their stability. Designers of performance multihulls, such as the Open 60's, go to great lengths to reduce overall boat weight as much as possible. This leads some to comment that designing a multihull is more similar to designing an aircraft.
Centerboard
The centerboard or daggerboard is in essence a very lightweight keel, which is not permanently mounted and can be pulled up to accommodate shallow water. Some sports boats are designed to plane on top of the water since they feature centerboards or light keels.
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