Selfish or cooperative? Understanding the behavior of ships during an overtaking process from the spatiotemporal perspective—A case study of Qingdao Port, China

Abstract

To understand the behaviors of ships at different stages of an encounter, this article analyzes the relative motion of ships during an overtaking process spatiotemporally. It takes the shortest distance between two ships as a boundary and uses the Douglas–Peuker algorithm and the difference algorithm to identify the critical points of the ship’s courses and speeds. The developed approach was demonstrated using data from the Qingdao Port Automatic Identification System (AIS data) and its adjacent waters. The results demonstrate that an overtaking ship extends a distance approximately 7 times its width (250 m) and a speed of 1.8 times that of the overtaken ship during the overtaking process to ensure safety. The preferences of around 90% overtaken ships for speed and course changes are similar, with a lateral offset distance of about 100 m. 73% of the ships show significant deceleration and cooperate with the overtaking vessels to shorten the overtaking time and maintain a safe lateral distance. The revealed patterns of behavior changes can be applied in further detail to simulation models of ship behavior in ports and adjacent waterways.