Sailing

Sailing is the skillful art of controlling the motion of a sailing ship or smaller boat, across a body of water. Sailing vessels are propelled by the force of the wind on sails. Today, for most people, sailing is recreation, an activity pursued for the joy of being on the water and pursuing the mastery of the skills needed to maneuver a sailboat in varying sea and wind conditions. Recreational sailing can be further divided into Racing, Cruising and "Daysailing."

Sailing Introduction
A boat moves as wind pushes on its sails. This is obvious when the boat is sailing downwind. The keel of a boat keeps it from strafing to the sides. This allows a boat to sail downwind but at an angle. The wind that blows on a sail is deflected off the sail, and that wind pushes against the sail too. The result is that the sail is not just pushed straight downwind, no matter which way it faces; but rather, it is pushed in the direction that it bows. This lets a boat point upwind, though at an angle and not straight upwind, to move forward as long as the sail is able to bow forward. If the sail is pointed just as the boat, then the boat will only be pushed sideways, yet if the sail is pointed into the wind, then it will not catch the wind at all. So, the sail must be pointed somewhere between.

A boat moves forward with a resultant force proportional to the dot product of the forward vector of the boat and the force vector of the sail on the boat. The force of the sail on the boat is parallel to the average normal vector of the sail and is proportional to the dot product of the relative wind vector and the average normal vector of the sail. This proportionality is most obvious because depending on the angle of incidence of the wind on the sail, the effective area of the sail varies. So, a positive value for a resultant force on the boat requires that the angle of the sail be bound between the forward direction of the boat and the upwind source.
When sailing downwind, a boat catches up to the wind, so the wind cannot push as hard on the sails. When sailing at an angle to the wind, however, although the boat may move fast, it is not catching up to the wind, so the wind continues to push the boat faster. Of course, eventually the boat cannot move faster because of the water, but not before speeding along much faster than if it had been sailing directly downwind.

The force on a sail is actually proportional to the relative velocity of the wind to the sail. Many factors complicate these generalities, however, such as the drag of the wind on the sails, the drag of moving through the water, the loss of wind force due to the boat heeling to a side so that the sails are pushed down and not just across the water.

The physics of sailing
The force of the wind is used to create motion by using one or more sails. When sailing downwind (away from the wind source) the vessel's motion is derived from the simple force of the wind pushing the sail. When sailing upwind (towards the wind source) the movement of air over the sails acts in the same way as air moving over an aircraft's wing. Air flowing over the sail generates lift. This pulls the sail (and the boat) ahead, but also pushes it downwind rather strongly. The downwind, or leeward, component is offset by an underwater hydrofoil whose shape resists lateral movement while offering little resistance to forward motion. Some hydrofoils even convert some of the leeward movement into forward motion. Without this hydrofoil, sailing upwind or across the wind would be virtually impossible. Sailing hydrofoils include keels, centerboards, and particularly in small sailboats the rudder acts as a hydrofoil also, reducing leeway.

The lifting force of the sails also acts to lean the boat over to one side, which is called heeling. Heeling is counteracted by ballast, either in the form of dense material located deep in the bilge or externally in the keel, usually lead or iron.

In ancient times ships used following or rear-quarter winds. Therefore, they had to either row or wait in port or at sea for the right wind directions.

Basic sailing techniques
The article Points of sail defines several terms that identify a sailboat's movement relative to the wind direction.

Steering and turning
When steering a sailboat, the method for changing direction depends on the direction of the wind. Thus, all direction changes or turns are described by one of the following terms:

Heading up (or luffing up) means steering so the wind is closer to coming from directly in front (or "on the bow"). Heading closer to the wind requires trimming the sails, pulling them towards the vessel's center. Heading up so the wind is nearly or directly ahead causes sails to luff, to flutter without achieving lift. If the boat loses maneuverability because of this, it is said to be in irons. Tacking (or coming about), one of the basic turning techniques, requires heading up and through the wind so it then comes across the oppposite side of the boat, and the boat sails away on the opposite tack.
Heading down, bearing away, and falling off mean steering so the wind comes from closer to the vessel's aft. This requires easing sails, letting them out away from the vessel's center. Jibing is the basic turning maneuver in which the boat heads down past the point where the wind crosses the vessel's stern, which causes the sails and boom to swing to the opposite side, before the boat sails off on the opposite tack.

Trim
An important aspect of sailing is keeping the boat in "trim". To achieve this a useful mnemonic (memory aid) is the phrase:

Sailing safety
First and foremost:

Stay on the boat!
Wear a life vest!
Learn to swim!
Sailing requires respect for the risks of being on the water. All sailors therefore should be sensibly prepared. Most jurisdictions have certain minimum regulations that must be met as to equipment. When engaged in publicly organized activities they may be required to take additional precautions, as detailed by the authority which regulates the training or racing.

Safety measures may include:

Appropriate floatation aids, including life preservers
Provision of a safety boat for rescue purposes
Appropriate first-aid and firefighting equipment
Carrying of a knife suitable for cutting rigging or netting in an emergency
Aside from what may be required by law or a sailing organization, real safety on the water comes from an informed awareness of risks involved and the exercise of reasonable steps to avoid dangers.
Understanding and practice of man overboard procedures such as the Anderson turn, the Williamson turn, and the Scharnow turn
Also, know the 'rules of the road':

Port tack gives way to Starboard tack (when the paths of two boats on opposite tacks cross, the boat with its port side to windward must give way)
Windward gives way to the leeward, or downwind boat (if on the same tack)
Overtaking boat gives way if above do not apply
Non-Commercial Powerboats usually give way to sailboats (but be careful in shipping lanes, and use common sense)
It is everybody's responsibility to avoid a collision, and avoiding action must be taken if these rules are ignored.

Types of sails and layouts
 
Traditional sailing off the northern coast of Mozambique.A traditional modern yacht is technically called a "Bermuda sloop" (sometimes a "Bermudan sloop"). A sloop is any boat that has only a single mast. 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. Addionally, Bermuda sloops only have a single sail behind the mast. Other types of sloops are gaff-rigged sloops and lateen sloops (sometimes called a junk-rig). 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 either 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 three-masted brigs.

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.

Sailing terminology

Sailors use many traditional nautical terms for the parts of or directions on a vessel; starboard (right), port (left), forward or fore (front), aft (rearward), bow (forward part of the hull), stern (aft part of the hull), beam (the widest part). Vertical spars are masts, horizontal spars are booms (if they can hit you), gaffs (if they're too high to reach) or poles (if they can't hit you).

Rope and lines
 
Standing rigging (on the left) and running rigging (on the right), on a sailing boatRope is the term used only for raw material; once a section of rope is designated for a particular purpose on a vessel, it generally is called a line, as in outhaul line or dock line. A very thick line is considered a cable. Lines that are attached to sails to control their shapes are called sheets, as in mainsheet (line that controls the mainsail) or spinnaker sheets.

Lines (generally steel cables) that support masts are stationary and are collectively known as a vessel's standing rigging, and individually as shrouds or stays (the stay running forward from a mast to the bow is called the forestay or headstay).

Moveable lines that control sails or other equipment are known collectively as a vessel's running rigging. Lines that raise sails are called halyards while those that strike them are called downhauls or cunninghams. Lines that adjust (trim) the sails are called sheets. These are often referred to using the name of the sail they control (such as main sheet, or jib sheet). Sail trim may also be controlled with smaller lines attached to the forward section of a boom; such a line is called a vang, or a kicker in the United Kingdom.

Lines used to tie a boat up when alongside are called docklines, docking cables or mooring warps.

Some lines are referred to as ropes: A bell rope (to ring the bell), a bolt rope (attached to the edge of a sail for extra strength), a foot rope (on old square riggers for the sailors to stand on while reefing or furling the sails), and a tiller rope (to temporarily hold the tiller and keep the boat on course). A rode is what keeps an anchor attached to the boat when the anchor is in use. It may be chain, rope, or a combination of the two.

The sport of Sailboat racing is governed by the International Sailing Federation (ISAF), and the rules under which competitors race are the Racing Rules of Sailing, which can be found on the ISAF web site.