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
Black Hands, White Sails: The Story of African-American Whalers it "A well-researched and detailed book " "Black Hands, White Sails" has also been reviewed by "The ALAN Review", "Kirkus Reviews", "The Horn Book Magazine". and "Voice of Youth Advocates", Black Hands, White Sails: The Story of African-American Whalers Black Hands, White Sails: The Story of African-American Whalers is a 1999 book by Patricia McKissack and Frederick McKissack about the involvement of African-Americans in the history of whaling in the United States. "BookList", in its review of "Black Hands, White Sails", called it a "fascinating look at the convergent histories of whaling and the abolitionist movement" and concluded "Less-skilled readers