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In geography and seamanship, windward (/ ˈ w ɪ n d w ər d, ˈ w ɪ n ər d /) and leeward (/ ˈ l iː w ər d, ˈ lj uː ər d /) are directions relative to the wind. Windward is upwind from the point of reference, i.e., towards the direction from which the wind is coming; leeward is downwind from the point of reference, i.e., along the ...
Standing on the leeward side of the vessel, a sailor observes being blown towards an exposed shoreline by the wind. Here again the reference point from which a shore is viewed determines whether it is the lee shore or a leeward shore. On a lake, the reference point is a body of water, so the windward shore is upwind of the center of the lake.
Lift on a sail (L), acting as an airfoil, occurs in a direction perpendicular to the incident airstream (the apparent wind velocity, V A, for the head sail) and is a result of pressure differences between the windward and leeward surfaces and depends on angle of attack, sail shape, air density, and speed of the apparent wind.
In sailing, lying ahull is a controversial method of weathering a storm, executed by downing all sails, battening the hatches and locking the tiller to leeward so the boat tries to point to windward but this is balanced by the force of wind and waves.
Conversely, a boat on an upwind course may find itself trapped in the dirty air of a boat immediately to windward. Right-of-way rules give priority to the leeward boat and can make it advantageous to be the boat without the weather gage, especially just before the start or when the boat to leeward can point higher into the wind.
The side of a ship toward the wind is called the "weather" or "upwind" side; away, the "lee" or "downwind" side (refer to Windward and leeward). Much has been made of the tactics of various great sailing captains, but the greatest constraints come from wind direction and relative position.
Weather helm is the result of a leeward and aft shift of a vessel's vector center of effort (the direction to which the force generated by the sails is pushing). This shift is caused by excess pressure on the mainsail , which overpowers the windward lateral resistance generated by the jib (or other head sail) and keel or centerboard.
The sand mass of dunes can move either windward or leeward, depending on if the wind is making contact with the dune from below or above its apogee. If wind hits from above, the sand particles move leeward; the leeward flux of sand is greater than the windward flux. Conversely, if sand hits from below, sand particles move windward.