Bottom contours are the shape of the bottom of the surfboard and influence how water travels under the surfboard. Some common surfboard bottom contours are:
Flat Surfboard Bottom Design
Flat surfboard bottom design is a fast bottom shape but one that can be difficult to control in larger/faster waves. Flat bottom is good for small, mushy waves, where you need lots of speed.
Concave Surfboard Bottom Design
Concave surfboard bottom design helps to prevent water being released under the rails giving the surfboard lift and speed. It is often used in the front section of Longboards to aid noseriding. On short surfboards a concave bottom will need increased rocker to allow the rider to retain good manoeuvrability.
Double Concave Surfboard Bottom Design
The double concave is seen on the majority of modern mainstream surfboards and is most likely the bottom contour your board has if you bought it straight off the rack at a surf shop. Generally the board will have a single concave from the nose which will gradually fade into a double concave towards the tail. The single concave provides a good planing surface, giving the board drive. The double concave splits the water into two channels through the fins and creates a much looser ride—great for those flowing maneuvers.
Vee Surfboard Bottom Design
Vee surfboard bottom gives a flat planing surface on each side of the surfboard that makes the surfboard fast through turns and easy to change direction. Vee surfboard bottom is not as fast when going in a straight line.
Surfboard Bottom Channels Design
Channel bottom design can have up to 8 channels running along the bottom of a surfboard and there are a number of variations. Their basic purpose is similar to a concave bottom i.e. To direct the water from nose to tail giving increased lift and speed. If they are deep, long and have hard edges they may do this too well and make the surfboard prone to tracking.