Ship Propeller Rotation Threshold to Prevent Erosion and Sedimentation in Coastal Waters

The rotation of a ship’s propeller can accelerate the water flow around it, which puts pressure on seabed particles. Continuous pressure on the seabed can significantly trigger erosion and sedimentation of coastal waters. Considering the impact that can be caused, the ship’s propeller rotation limit needs to be determined to avoid damage to the aquatic ecosystem. This research determines the threshold of ship propeller rotation based on the water flow velocity characteristic. Research has been carried out at the Hydrodynamics Laboratory on several variations of propeller rotation R_rmp (r/min) and water depth using empirical approaches, numerical simulations, and scale model experiments. Analysis based on general standard criteria for erosion and sedimentation shows that a propeller with a diameter (D_p) of 1.5 m is safe for propeller rotation at 25 r/min at all water depths. Then, the propeller rotation of 75 r/min is safe for a distance between the propeller axis and the bottom of the water equal to D_p. Meanwhile, rotation at 120 r/min is safe at a minimum distance of 1.5 D_p, and 230 r/min is safe for a minimum distance of 2.0 D_p. The propeller rotation threshold criteria are essential to determining the new under-keel clearance for environmentally friendly ship operations. Threshold values vary based on seabed particle type and water depth.