Experimental and Numerical Analysis of the Drag Force on Surfboards with Different Shapes

Abstract

The aim of the present study is to define the hydrodynamic resistance of surfboards with different designs. Decreasing the drag acting on a board helps the surfer to attain higher surfing performances. It helps to attain higher speeds and maneuvering for the surfer. In this thesis, theoretical, experimental and computational approaches are used to explain how the drag changes with different surfboard shapes. Four surfboards with varying shapes were towed at different speeds and the resulting force was recorded. Two computational models were developed using Star CCM and Flowsquare to confirm the experimental results. The drag force on the boards increases with increasing area. The increased wetted surface area resulted in increased buoyancy but decreased mobility. The drag force could be broken down into frictional and form drag. Form drag is a function of the shape of the object and decreases with improved surfboard design, like pinned tail instead of squared. Longer surfboards attain planing mode at higher speeds. Displacement mode is dominated by form drag whereas planing mode is dominated by frictional drag. Drag coefficients for the various boards ranged from 0.1 at low speeds to 0.05 at high speeds. Shorter surfboards had higher drag coefficients because of higher shear stress.