# Factors Influencing the Action Point of the Collision Avoidance Manoeuvre
## 1 Introduction  
Human error remains one of the most common causes of maritime accidents [1; 2; 3], responsible for between 40% and as much as 90% or even more of accidents [4; 5; 6]. This applies in particular to collisions, largely because in most cases of such potential danger, both parties must make the correct decision for ships to pass safely. According to the Convention on the International Regulations for Preventing Collisions at Sea (COLREG) [7] an encounter situation can be divided into four stages: when the distance between ships is great enough to assume that there is no risk of collision, and ships are free to take any action; when the distance has decreased to the degree that there is a risk of collision and the give-way ship is required to take action, and the stand-on ship must keep her course and speed; when it is clear that the give-way ship is not taking action thus that stand-on ships are permitted to take action to avoid collision; and when it is not possible to avoid the collision by the give-way ship manoeuvre and the stand-on ship must take action to avoid the collision. Quite naturally, too many variables are present at any given time for COLREGs to offer defined times or distances when the given stages begin and when the actions should be taken. Rule 8 states that \"Any action to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship\". Rule 16 adds that \"Every vessel which is directed to keep out of the way of another vessel shall, thus far as possible, take early and substantial action to keep well clear.\" This is where science is mocked by common sense, essentially, some of the best experts in navigation have been reduced by the difficulty of the task to the maritime equivalent of driving instructors: Try not to hit anything. Based on such ambiguous yet obvious information, it is difficult to build a collision-avoidance decision model that would reflect the navigator's behaviour in collision situations. Nonetheless, the development of such models is necessary to enhancemaritime safety by improving navigation intelligence and autonomy in a technical way while avoiding decisions based on subjective experience, thereby eliminating human error to the greatest degree possible [8,9]. The crucial questions required to model the decision-making process are when to begin collision-avoidance manoeuvres and what factors should be taken into account. According to [PERSON] [10], the distance between ships at the moment the give way ship starts the manoeuvre should be between 5 to 8 NM on the open sea. However, this distance can vary depending on the prevailing conditions, mainly influenced by traffic intensity, size of the available area, type of encounter, speed and relative speed of the ships, size and manoeuvrability of the vessel, visibility, etc. In other words, just about every variable one can conjure [11,12]. Most of the research on decision-making is based on indirect data, methods such as expert studies or analysis of AIS records [13, 14, 15]. The other approach is to analyse the actions taken by navigators in simulated conditions [13,16, 17, 18]. [PERSON] et al. [19] determine the action point of collision-avoidance to minimise fuel consumption while ensuring the operational safety of the ship. [PERSON] et al. [20] calculated collision-avoidance in heavy traffic areas with a very short distance. On the other hand, [PERSON] et al. [21] estimated the safe distance to start collision-avoidance manoeuvre was 8 NM, Ni [22] performed trajectory planning for collision-avoidance, using action point at 6 NM for crossing and head-on situation, and 3 NM for overtaking situations. Some authors did not specify an action point distance but focused on solving the problem by ensuring a safe passing distance [23, 24, 25, 26, 27, 28]. The present work aims to identify the most important factors influencing the action point in collision situations.