Surfboard Bottom Contours
DJ Stanfill

3 Basic Bottom Contours:

-generate speed but otherwise plain (no lift, no flow direction)
-good for building speed on a plane
-usually found near nose of performance boards

Concave (single, vee/double, or teardrop/spoon-like):
-generate lift and laminar flow
-good for control / holding a rail due to lift and slightly larger surface area
-usually found towards middle of the bottom, though depends on board type; tails often have double concave near fins to direct water through fins

Convex (smooth "belly" or flat vee):
-keeps board out of water / easy to disengage
-good for rail transitions and stability (depending on board)
-flat vee usually found near tail of all boards; especially common on longboards (when on nose prevents pearling); some shortboards have a short convex vee following a double concave at the tip of the tail to help rail-to-rail transitions

3 Common Blending Examples (no single right way of doing this!):

Performance Shortboard (bigger days)
-Nose: flat for speed
-Middle: concave for lift and rail control
-Tail: double concave (lift and control for back foot) blended into flat vee (easy to disengage for rail transitions)

Hybrid (small days but ripping power)
-Nose: belly (convex) for displacement / pearl prevention
-Middle: single concave for lift and control
-Tail: blended flat for speed, blended again into vee for rail-to-rail

Longboard (log with deck-walking potential)
Nose: tear-drop concave to generate lift when towards nose, also helps with rail control when surfing from front
Middle: belly convex for stability and rail transitions
Tail: blended vee to help with rail transitions and hard turns