Twin propeller scour in noncohesive seabed with different quay wall configurations

Propeller-induced scour presents a significant challenge to the structural integrity of seabeds near quay walls. This study explores the scour phenomena produced by co-rotating twin propeller under different quay wall configurations on a noncohesive seabed. Laboratory experiments were performed using sand with a median grain size (d₅₀ = 1.2) and within a densimetric Froude number range of 4.71–6.23. The study also explores the influence of propeller spacing, speeds, and gap distances on scour characteristics. Under unconfined conditions, the scour profiles generated by twin propellers with spacings of two and three times the propeller diameter (D_p) were similar to those observed with single propellers, albeit with increased scour depths. For these propeller spacings, similar scour hole formation (single scour hole) was also observed and the width of the scour hole is greater in proportion to its length in the twin propeller tests. Novel empirical equations were derived to predict maximum scour depths for no-wall, vertical, and parallel quay wall conditions. These equations demonstrated strong correlation with experimental data, achieving determination coefficients of 0.99, 0.99, and 0.98, respectively. The findings contribute to the understanding of twin-propeller scour dynamics and provide practical tools for designing and assessing quay wall stability in ports.