<p>The T-shaped hydrofoil, consisting of the surface-piercing strut and submerged hydrofoil, plays a crucial component of a hydrofoil system. This study investigates the hydrodynamic performance and flow patterns of the T-shaped hydrofoil under varying flow parameters and geometric characteristics, utilizing towing tests and large eddy simulation (LES) techniques. The computational and experimental results demonstrate a high degree of agreement. The analysis reveals that both lift and drag coefficients increase with the angle of attack. As the Reynolds number increases, the drag coefficient decreases, while the lift coefficient remains relatively stable. When the T-shaped hydrofoil is deeply submerged, the free-surface deformation primarily manifests as spray flows. Notably, the free surface effect becomes significant at submerged depths shallower than 3.5 times the chord length. As the submerged depth decreases, the free-surface depression in the wake is enhanced; however, both the lift and drag coefficients of the T-shaped hydrofoil decrease, governed by the S foil and strut, respectively. The incorporation of winglets plays a vital role in optimizing hydrodynamic performance by redistributing tip vortices away from the hydrofoil, thereby reducing the vorticity and spiral motion induced by the tip effect. Additionally, the interference effect from the strut enhances both lift and drag performance of the submerged hydrofoil, although it may also lead to an earlier cavitation inception. The increased lift and drag can be primarily attributed to the lateral spread of negative pressure arising from the separation region on the strut.</p>