Rapidly increasing numbers of ships and ship sizes pose an ever-growing challenge to the maritime industry. Although statistics indicate improved levels of safety in the industry which carries 90% of the world’s trade, the risk of navigational accidents, among other issues, remains a prime concern and priority (EMSA, 2010; 2014). In order to address these concerns, the authors turned to another high-risk industry for inspiration. Specifically, they turned to the aviation industry, which has often been used as a source of comparisons and ideas by researchers in the maritime domain. Keeping up with the trend, the authors of this paper turn to a tried-and-tested system used widely in modern aviation: the Airborne Collision Avoidance System (ACAS). The prime idea behind ACAS is to construct two virtual 3D zones around an aircraft. These zones are dynamic, and depend on the manoeuvring characteristics of a given aircraft. If the system detects an “intruder” (another aircraft) in either of the two well-defined virtual zones, it provides warnings and/or instructions to pilots of both aircraft to take certain precautionary or emergency measures. In the current paper, the authors explore whether or not such a system is feasible for use in the maritime domain and, if so, how. The paper provides a detailed analysis of the potential benefits and drawbacks of using an ACAS-like system onboard vessels. It also discusses possible means of implementation and integration with current equipment, and explores how the introduction of e-navigation may impact the proposed solution.

Avoidance of collisions is one of the most important tasks for the officer of the watch on a ship’s bridge. Measures and actions required to avoid such accidents are described in the Convention on the International Regulations for Preventing Collisions at Sea (COLREGs) adopted by the International Maritime Organization (IMO) in 1972 and still valid, with several minor amendments, since then. On the basis of a proper look-out at all times, by sight and hearing, and the use of all available means, also including technical equipment installed on-board as well as information provided by a Vessel Traffic Service (VTS), the navigating officer collects traffic and environmental data and combines them with their own ship data to construct a mental traffic image for the assessment of risk of collision with other objects in the vicinity. In the case wherre there is an unacceptable risk she or he has to decide on taking action. In most of the cases decision making is appropriate to the prevailing circumstances and ships maneuver and pass at a safe distance. Only in very rare cases, due to whatever reasons, watch officers fail in taking appropriate actions in good time. It is assumed that, if effective alerting algorithms would be available, a substantial number of collisions at sea, and especially in coastal waters, can be avoided by making the watch officer aware that the ‘last line of defence’ for taking action is close to come. It is assumed that there is potential in applying the principle of the resolution advisory alert of an ACAS (Airborne Collision Avoidance System)/TCAS (Traffic Alert and Collision Avoidance System) in aviation and adapt it to the needs of maritime traffic. In this paper, the authors introduce a method for triggering collision warnings by focusing specifically on the critical last phase of an encounter and taking into account the maneuvering characteristics of the navigating ship. They comprehensively explore the application using scenario studies discussing the operational aspects of varying implementation states (one ship only, SOLAS ships only).