Comparative Collision Risk Framework for Wind-Assisted Ships: A Case Study between the English Channel and the Port of Santos
Abstract
Wind-Assisted Ship Propulsion (WASP) has emerged as a leading solution for maritime decarbonization. To date, no published research has addressed the specific relationship between this technology and navigational safety. While traditional collision risk metrics like the Closest Point of Approach (CPA) are designed for local, tactical navigation, the wind-dependent trajectories of Wind- Assisted Ship Propulsion (WASP) vessels necessitate a strategic, route-wide assessment. Based on the optimal routing simulator from the SOlver MOdular and Simulator for WASP (SOMOS project), this study proposes a novel methodological framework to evaluate collision risks on a global-scale, applied to a representative route between Santos, Brazil, and the English Channel. Each routing is computed independently based on real wind conditions, without integrating COLREG-compliant avoidance maneuvers, thus assuming that ships navigate independently from one another. By evolving the Closest Point of Approach (CPA) method into a large-scale spatio-temporal risk analysis, the proposed approach acts as a pre-filter for applying frequency and intensity-based Safe Boundary methods. One-year simulations comparing conventional and mixed fleets, with ships equipped with two Flettner rotors, indicate that while the overall frequency of risks may decrease, the statistical distribution shifts toward more severe encounters in mixed fleet scenarios. The study also shows that different fleet scenarios create different types of effects that can be identified. This work provides a new methodology for quantifying how wind-dependent pathing reshapes maritime risk, offering essential insights for the safe integration of wind propulsion systems into global shipping traffic. Wind-assisted ship propulsion (WASP); collision risk assessment; maritime traffic safety; closest point approach (CPA); safe boundary approach; route-scale evaluation