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Collision Avoidance for Underactuated Ocean-Going Vessels Considering COLREGs Constraints

Ocean-going vessels usually sail at a constant speed in open sea. Rule 8 of the International Regulations for Preventing Collisions at Sea (COLREGs) recommends alteration of course as the single most effective way to avoid collisions. This makes the study of constant speed collision avoidance (CSCA) critical for the development of automatic navigation systems for ocean-going vessels. This paper presents a 4-DOF MMG ship motion mathematical model that can capture the maneuvering characteristics of a ship using collision avoidance (CA). Drawing upon a velocity obstacle (VO) method, a velocity-derived heading obstacle algorithm (VHO) that meets COLREGs (Rule 8, 13, 14 and 15) constraints is proposed. The algorithm does not control the speed of the ship, but rather guides its course to prevent collisions. To aid determination of when CA action should be employed, a new function is also defined. CSCA simulations for scenarios involving both two ships and multiple ships were designed and carried out. In simulations, all ships could avoid other ships, keeping a distance of more than 1 nautical mile from each other, which demonstrates that the VHO algorithm ensures that ships can always keep a safe distance from other ships.