Safety-Enhanced Berthing Control Strategy for Surface Ships Using Backward and Forward Reachability Analysis

Abstract Surface ships generally have limited control authoritfy for precise point stabilization, making automatic berthing a challenging task, particularly under real-world environmental disturbances. In practical berthing operations, the final berthing point and a nominal trajectory are typically predetermined. Nevertheless, an important challenge remains in verifying whether a selected initiation state along the approach can lead the vessel to the terminal berthing set within a prescribed time window under limited maneuverability and actuator constraints. This study proposes a reachability-analysis-based control framework that adds feasibility verification to such preplanned maneuvers and disturbance compensation. Backward reachability analysis is employed to compute an admissible initiation envelope, i.e., the set of states from which the vessel can reach the final state within the required horizon under its dynamics and input limitations. This envelope supports pre-berthing planning by identifying feasible initiation states and screening candidate starting conditions. Forward reachability analysis is further used to predict wind-induced deviations under bounded disturbances and to construct an auxiliary compensation input for safety-enhanced berthing execution. Numerical simulations verify that the proposed framework effectively identifies valid initiation conditions and improves the safety of the final berthing process.