Assessment of a critical area for a give-way ship in a collision encounter

Evasive action in ship-ship encounter has to be carried out on time and in line with the international convention on collision regulation – COLREG. The convention not only includes a set of rules defining types of relations between encountering ships but also indicates appropriate action to be taken in a given encounter. One of such encounters is crossing, where, in case of a collision situation, a give-way ship has to take an appropriate action in due time. However, a stand-on vessel is also given an opportunity to manoeuver, if it is made clear to her that the other ship is not fulfilling her obligations. However, it is difficult to specify, at which point in time in the course of an encounter, the stand-on ship has to take an action in order to avoid collision. It is understandable, as this parameter depends on numerous factors, both endogenous (e.g. ship characteristics, her maneuverability), and exogenous (e.g. type of encounter, weather conditions). Therefore in this paper we make an attempt towards the definition of the critical area for a maneuver of a stand-on ship, in the situation where the give-way vessel does not take an action. This is determined with the use of a hydrodynamic model of ship motion, and series of simulations conducted for several types of encountering ships under various conditions. Once determined, the critical area demarcates the no-go area around the own ship, where any other ships on collision courses must not enter. Otherwise a collision cannot be avoided by an action of one ship alone.