Recreational sailing or yachting can be divided into racing and cruising.
All sailing craft reach a constant forward velocity (V) and point of sail.The craft's point of sail affects its velocity for a given true wind velocity.Conventional sailing craft cannot derive power from sails on a point of sail that is too close into the wind.On a given point of sail, the sailor adjusts the alignment of each sail with respect to the apparent wind direction (as perceived on the craft) to mobilize the power of the wind.According to Jett, the Egyptians used a bi-pod mast to support a sail that allowed a reed craft to travel upriver with a following wind, as late as 3,500 BCE. Running (drag)— 180° True wind (V The physics of sailing arises from a balance of forces between the wind powering the sailing craft as it passes over its sails and the resistance by the sailing craft against being blown off course, which is provided in the water by the keel, rudder, underwater foils and other elements of the underbody of a sailboat, on ice by the runners of an ice boat, or on land by the wheels of a sail-powered land vehicle.
Such sails evolved into the square-sail rig that persisted up to the 19th century. Forces on sails depend on wind speed and direction and the speed and direction of the craft.The lift force results from the average pressure on the windward surface of the sail being higher than the average pressure on the leeward side.These pressure differences arise in conjunction with the curved air flow.The earliest representation of a ship under sail appears on a painted disc found in Kuwait dating between 50 BCE.Advances in sailing technology from the Middle Ages onward enabled Arab, Chinese, Indian and European explorers to make longer voyages into regions with extreme weather and climatic conditions.There were improvements in sails, masts and rigging; improvements in marine navigation including the cross tree and charts, of both the sea and constellations, allowed more certainty in sea travel.