Forces on sails to stay within the limitations of a craft's stability and power requirements, which are functions of hull (for boats) or chassis (for land craft) design. Sails derive power from wind that varies in time and with height above the surface. In order to do so, they are designed to adjust to the wind force for various points of sail. Both their design and method for control include means to match their lift and drag capabilities to the available apparent wind, by changing surface area, angle of attack, and curvature. Wind speed increases with height above the surface; at the same
Forces on sails force component (F), is the most significant rotational effect of total aerodynamic force (F). In stasis, heeling moment from the wind and righting moment from the boat's heel force ("F" ) and its opposing hydrodynamic lift force on hull ("F" ), separated by a distance ("h" = "heeling arm"), versus its hydrostatic displacement weight ("W" ) and its opposing buoyancy force ("Δ"), separated by a distance ("b" = "righting arm") are in balance: Sails come in a wide variety of configurations that are designed to match the capabilities of the sailing craft to be powered by them. They are designed