3 Basic Bottom Contours:

Flat: 
-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
Surfboard Bottom Contours 
Added 2 years ago by DJ Stanfill
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Surfboard Bottom Contours 
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3 Basic Bottom Contours: Flat: -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
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