*2.2. Propeller Induced Scour*

Chiew and Lim [18] studied the scouring problem by using a submerged circular jet to simulate the rotating propeller instead of the complicated propeller jet. The scour hole dimensions produced by the circular wall jet were highly dependent on the densimetric Froude number ( *F*0). The maximum equilibrium scour depth increased with an increase in *F*0. Chiew and Lim introduced the o ffset height (*G*) of the circular wall jet as an additional parameter governing the di ffusion characteristics of the jet. The maximum scour depth reduced with an increase in the o ffset height.

Hamill et al. [11] investigated the scour induced by a propeller jet both in the absence of the port structure and near the quay walls. A predictive equation for the time-dependent maximum scour depth as a function of the Froude number (*F*0), propeller size (*Dp*), sediment bed material size (*d*50), and distance between propeller tip and seabed was proposed. Seabed scour around a marine current turbine was also studied by Chen and Lam [19].

**Figure 1.** Flow structure of a twin-propeller jet [15].

Hong et al. [10] conducted an experimental study of a single propeller jet. Limited works from Mujal-Colilles et al. [20] and Yew [16] were found to discuss the twin-propeller induced scour. All these researchers stressed the importance of estimating the maximum scouring depth caused by ship propeller. The equations to predict the scour depth proposed by the previous researches are shown in Table 1.


**Table 1.** Summarised scour depth induced by the propeller.
