The art of sailing incorporates the interaction of the wind, water and the vessel's form to
enable the boat to move toward its destination. The sailor must understand how to use
these forces most efficiently to propel his vessel.
Before harnessing the power of the wind, the sailor must understand the dynamics of
their vessel's underwater and above water features. The underwater structures of the
sailing vessel include a rudder and a keel. The rudder is a vane that deflects the moving
water, enabling the vessel to be steered. The keel is an underwater fin that prevents the
force of the wind from simply pushing the vessel sideways. The sideways movement of
the vessel is called sideslip or leeway. The keel not only prevents sideslip but also is
ballasted (filled with weight) to counteract the force of the wind on the sails and masts
Mounted on the deck or stepped through the deck onto the keel is the mast, is
supported by wires. The wires keep the mast upright in the vessel. Wires leading
foreword and aft are called stays. They position the mast along the centerline of the boat.
The wires leading to the side rails of the vessel, shrouds, center the mast laterally in the
middle of the vessel. Sails are raised and lowered by the use of control lines called
halyards. Usually the halyard is named after the sail it controls, for example the main
halyard controls the lowering and raising of the mainsail. Sheets are the lines that control
the inboard or outboard positioning of a sail. Again, the sheet that adjusts a sail is usually
named after the sail it adjusts. The jib sheet adjusts the jib sail.
To efficiently harness the power of the wind the sailor must understand how a sail powers a
vessel. Sails use the force of the wind in two different ways. With the wind blowing from behind,
the vessel is pushed along by the wind. The pushing principle works well for sailing before the
wind, but how does the vessel sail toward the direction of the wind?
The example of the airplane wing is often used to explain how a sail develops lift. When air moving past the Wing approaches the leading edge of the wing it separates and some of the air passes over the wing's curved surface and some passes across the relatively flat underside. The air
passing over the wing must speed up, because it is traveling a greater distance, to arrive at the trailing edge at the same time as the air that had passed under the wing. This causes a decrease in the air pressure on the top of the wing. The wing is pushed up. This force is called lift. This is known as the Bernoulli Principle.
Taking a wing and mounting it vertically on a platform and you now have a sail. The lift generated by the adjustment of the angle of the sail to the direction of the wind enables the vessel to sail towards the wind. The lifting force developed by the sail is adjusted with the direction of the rudder and the resistance of the keel to side-slip (leeway) to allow the sailor to sail the vessel in a wide range of angles relative to the wind direction.