We see many types of shapes on the bottom of surfboards, for example on longboards, we often see the “vee” shape, but how does it work?
Our weight, the force of thrust on the turn and the wave force, shifts the water to the sides away from the stringer, releasing pressure in the center of the longboard creating buoyancy. In all my longboards, my favorite type is a “Rolled bottom to vee”.
In the Classic Single fin, I almost always use the concave single which works by directing the water flow to the tail and progressively to the sides, creating extra buoyancy in different parts of the board. The last two retrofish that I have done, have been with a double concave. This works almost the same as the single concave, with the difference being that in this case, it has two concaves and therefore, two forces that act towards the sides and upwards creating extra buoyancy.
A fun part of working is shaping the channels but also, how not, to try them. A simple way to understand how it works is the concaves also work as mini fins which give the surfboard extra grip.
It is important to understand how the different elements of our board behave, since these make it work in one way or another, and therefore shape our preference.