Adaptive Formation Control for Marine Vessels with COLREGs-Compliant Collision Avoidance in Dynamic Environments

Ensuring collision-free navigation for Maritime Autonomous Surface Ships (MASS) in congested maritime environments is a critical challenge. This paper presents a path-planning and collision avoidance framework based on the Non-uniformly Distributed Velocity Field Guidance Method (AFMS), enabling COLREGs-compliant multi-vessel operations. The method dynamically modulates the velocity field around static obstacles and neighboring vessels, facilitating efficient navigation while maintaining regulatory compliance. A zone-based encounter detection module classifies relative bearings according to COLREGs and triggers context-specific guidance strategies. An adaptive elliptical formation model coordinates vessel geometry, while a velocity synchronization mechanism ensures propulsion consistency during avoidance and formation maneuvers. MATLAB/Simulink simulations in representative offshore scenarios demonstrate effective handling of head-on, crossing, and overtaking encounters, preserving formation stability, smooth trajectories, and safe inter-vessel distances. Results confirm real-time responsiveness, regulatory adherence, and robust threat mitigation. The proposed framework offers an interpretable, scalable, and reliable solution for autonomous maritime operations in constrained, obstacle-rich waters.