Ship-induced waves at Tybee Island, Georgia

Commercial vessels transiting the Savannah entrance channel intermittently generate large wake events at Tybee Island, Georgia, creating a potential hazard for beachgoers. However, not all commercial vessels generate large wakes, and the relationship between vessel dimensions, operating conditions, wake height, and drawdown magnitude is unclear. This study evaluates bathymetric data, high-frequency wave and vessel wake measurements, and broadcast vessel identification over a 4-month period with the goal of providing a quantitative characterization of vessel wake conditions at Tybee Island. Data from 1,386 cargo vessel passages and 202 tanker passages indicate that vessel dimensions (length and beam) are positively correlated with drawdown magnitude and secondary wake height, although large vessels do not consistently generate large wakes. Container ships, which tended to travel faster than tankers, corresponded to the largest wakes in the dataset. A further hypothesis is that tidally modulated energy dissipation may favor smaller vessel wake uprush at low tide and larger uprush at high tide, but this idea cannot be confirmed without additional measurements to quantify nonlinear wave propagation on the beach face. Based on the collected data, the study concludes with four recommendations for reducing risk to beachgoers.