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
Polytarp sails 14 or 14 x 14. Increasingly, white polytarp is used to construct mainsails, jibs, and mizzens, while the lightweight polytarp materials are reserved for making spinnakers. Polysail is the term given to any sail made of polytarp material and not just the white polytarp material. Polytarp is used to construct nearly every type of sail. However, the material is best for traditional sail types such as sprits, lugs, gaffs, gunters, lateens, junk sails, and jib-headed sprits. They are not suitable for sails that depend upon being highly tensioned, such as the marconi or Bermuda types of triangular sails. Polytarp sails