A depressed area on the bottom of the surfboard. California board designer Bob Simmons experimented with longitudinal concave in the 1950s, on the premise that the indented section would trap air and "lift" the board, increasing speed. But concave didn't really catch on as a design feature until the mid-'60s, when it was put into the board's nose section as an aid to noseriding. The Ego-Builder Co...

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