The turbulent flow past a surface-piercing finite cylinder at Re = 2.7×10⁵ and Fr = 1.1 is analyzed in depth using the dynamic mode decomposition (DMD) method, where the velocity fields at three representative depths serve as two-dimensional snapshots. According to the frequency spectra, the dominant DMD modes can be divided into low-frequency () and vortex shedding () regions. In the low-frequency region, the two clusters of DMD modes are due to free shear layers () and the free end (), respectively. Furthermore, the disappearances of vortex shedding modes at z/D = −3.5 and free end modes at z/D = −0.75 indicate the inhibition of Karman vortex shedding near the free end and the negligible free-end effect near the free surface.