Editing Surfboard (section)

===Bottom===
[[File:Surfboardbottoms.jpg|thumb|A chart showing various shapes of the bottoms of surf boards.]]
The surface of the board that rests on the water is usually flat or concave but sometimes convex. The bottom can also feature channels, chines, steps and other planing features shaped into the board in order to maximize, direct or alter water flow across the board's bottom surface.

====Concave====
Modern surfboards often contain multiple contours on the bottom of the board, termed ''concaves''. These concaves have different uses and vary among different types of surfboards. Most concaves on the modern shortboard begin about {{convert|30|cm|in|abbr=on|sigfig=2}} back from the nose of the board on the bottom and then carry out through the middle to the tail of the surfboard. The purpose of concave is to direct water through the fins of the surfboard. Surfboard shapers sometimes experiment with concaves to create different drive and response characteristics on each individual surfboard.

====Convex====
Some older and more traditional surfboards along with many modern boards that take inspiration from these older boards utilize a convex rather than concave design on the bottom of the surfboard. These boards displace more water and sit lower in the wave than a surfboard with a concave bottom.<ref>{{Cite web|author=John Dang|url=http://www.surfscience.com/topics/surfboard-anatomy/bottom-contour/displacement-hulls|title=Displacement Hulls|website=surfscience.com|access-date=2010-02-13}}</ref>