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
Sails of Silver the present. Every album they have released since "Sails" has had at least one song written by band members, and "Back in Line" and "Bloody Men" were predominantly the band's material. Maddy Prior has said that, although she likes the album and finds it accessible, the band was in her words "lost" and not particularly confident of the material it had put together. Fans found the album jarring, although they were pleased that the band was touring again, and the band's shows always included their earlier material. When the album was reissued in 1998, three bonus tracks were included: The