Forces on sails (3 m) = 5-m/s (≈10-knot) wind at 3 m above the water would be approximately "V" (15 m) = 6 m/s (≈12 knots) at 15 m above the water. In hurricane-force winds with "V" (3 m) = 40-m/s (≈78 knots) the speed at 15 m would be "V" (15 m) = 49 m/s (≈95 knots) with "p" = 0.128. This suggests that sails that reach higher above the surface can be subject to stronger wind forces that move the centre of effort ("CE" ) higher above the surface and increase the heeling moment. Additionally, apparent wind direction moves aft with
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