Belly Bottom
The belly or displacement hull bottom has a convex planing surface typically found towards the front 1/3 of the board. This is designed for control. It gives it a smoother ride in choppy conditions.
In big and fast surf, it makes it easier to roll which means it is easier to lean from rail to rail. This is essential for controlling your board at high speeds.
The design is useful in bigger surf, where speed is not an issue and control is more important. The downside is the surface's inefficiency.
Energy is lost when water is parted and escapes from the rails, which slows the board.
This forces the board to work harder to move because it has to plough through water rather than skimming on top of it.
