Hydrodynamic Response and Safety Thresholds for Ships in Ultra-Confined Ship Lift Chambers: A Large-Scale Experimental Study

Ship transit in vertical ship lift chambers represents a highly confined flow regime characterized by extreme blockage (N < 2), where ship-induced piston effects can significantly influence navigational safety and structural loads. This study presents an experimental investigation of the unsteady hydrodynamic responses of a 1000 t class ship operating in the Baise vertical ship lift. A 1:10 large-scale physical model was constructed to reproduce the ship lift chamber and auxiliary lock geometry under Froude similarity. Tests were conducted for prototype water depths of 3.7–3.9 m and sailing velocities between 0.4 and 1.1 m/s. Ship sinkage, free-surface oscillations, and dynamic chamber weight variations were synchronously measured. Results revealed a profound process asymmetry: the exit maneuver induced significantly higher sinkage (0.92 m at 1.1 m/s) and chamber weight fluctuations (810 t) than the entry process due to restricted return flow replenishment. A non-dimensional predictive P–K relationship was derived with a regression coefficient α = 1.9121. Based on safety margins and mechanical load limits, critical speed thresholds were established at 0.6 m/s for exit and 0.7 m/s for entry to ensure a minimum safety clearance of 0.48 m even under docking error conditions.