Good surfers instinctively use transverse flow without thinking about it. Two examples are pumping a board to generate speed in flat section or doing a quick top turn to get up to speed. Pumping a board in a flat section rolls the board up on a rail to make the flow run transversely across the bottom to generate more lift. As the board is pumped in a turn, the board is aligned parallel to the wave crest which results in the flow coming up the wave face moving transversely across the bottom. Doing a quick top turn also rolls the board up on a rail and it aligns the board parallel to the wave crest which both create more transverse flow. Obviously, it works on flat bottom boards as well as boards with moderate concave, but it works better on a Camber Surfboard with a higher exit angle at the rail that functions like a flap to generate higher pressure under the board.
We use Computational Fluid Dynamics (“CFD”) to predict lift versus drag (L/D) for various bottom contours with different design conditions. A CFD program divides the water into millions of cells and then solves the basic fluid dynamics equations for each cell. The CFD results include the flow velocity and pressure in each cell yielding a color-coded pressure distribution map making it possible to compare different bottom pressure contours and resultant forces at various pitch, yaw and roll angles, as well as different speeds and rider weights. Bright purple represents the highest pressure and blue represents the lowest pressure.
The images below illustrate a CFD prediction of the difference between the pressure distribution on identical boards. The difference is that the board on the left has a typical concave 0.18 inches deep with the deepest point located 18 to 24 inches up from the tail which is typical for a conventional short board, whereas the CAMBER Surfboard on the right has a concave of modest depth and optimized contour in the area adjacent to the rail. The CFD runs for each board were done at the same pitch, roll and yaw angles as well as the same wave speed and wave contour. Purple represents the highest pressure and blue the lowest pressure. It is easy to see that the board on the right is generating far greater lift based on the colored pressure contours particularly near the stagnation line region.