The effect of submerged vertical breakwater dimension on wave hydrodynamics and vortex generation around the breakwater is investigated with numerical modeling via two dimensionless parameters: the breakwater dimensionless submergence depth (a/H i; a-the breakwater depth of submergence) and the Keulegan-Carpenter number (KC = H i/L bw; H i-incident wave-height and Lbw-breakwater width). In the numerical model, Reynolds Averaged Navier-Stokes (RANS) equations with a standard k–ε turbulence closure model were implemented; the free surface was traced using the VOF method. A total of 10 different simulations with different KC number and breakwater submergence depth were conducted for this study. The results revealed that the transmission coefficient increases with increasing a/H i and KC number, but that the effect of the KC number is not linear like the relation to a/H i. For the waves modeled, the transmission coefficient increases dramatically with increasing the KC number until the KC number reaches a critical value, this critical value is observed when breakwater width is equal to a quarter of wavelength. This gives a hint in design of breakwater width. Turbulence intensity decreases with increasing a/H i and KC on the seaside of the breakwater while it increases especially near the bed on the leeside of the breakwater; this can increase scour risk on the leeside of the breakwater. The optimum a/H i for both, high-energy dissipation rate and low risk of scour tends to 3.5 for KC ≈ 1.0.