Comparison of Vibration Damping Characterization of Two Surfboards Using the Free-Decay Logarithmic Decrement Method

Abstract: This study reports the vibration damping of two polyurethane (PU) surfboards of different sizes and shapes . The method used for this study is the free-decay logarithmic decrement method. An inertial measurement unit (IMU) accelerometer was fixed at the midpoint of each board. An impulse excitation was applied at the same location using a hammer, and the resulting acceleration signal was recorded along the board's out-of-plane axis (Z-axis). The logarithmic decrement δ was computed from consecutive peak amplitudes, and the damping ratio ζ was given. Three trials were conducted per board. Trials with negative ζ values were rejected. The retained damping ratios are ζ = 0.1979 for Board A (Brain Yuki Just Foam, shortboard) and ζ_mean = 0.178 for Board B (Island R, funboard). The approximate 10% difference between the two boards is discussed in the context of board geometry, mass distribution, and the test setup limitations. These results constitute a preliminary mechanical baseline that can support future surfboard selection and optimization tools.

Keywords: surfboard; vibration damping; logarithmic decrement; damping ratio, free-decay, accelerometer; composite materials; polyurethane foam.