Determining and visualizing safe motion parameters of a ship navigating in severe weather conditions

The paper presents a method of determining, organizing and displaying ship collision avoidance information, which is based on the Collision Threat Parameters Area (CTPA) technique. The method makes it possible to visualize navigational threats as well as possible collision avoidance manoeuvres. The solution is focused on supporting navigation in severe weather conditions. Normally collision avoidance decisions are made taking into account targets' motion parameters, International Regulations for Preventing Collisions at Sea (COLREGS) and navigational obstacles. However, in hard weather conditions each manoeuvre has to be additionally checked to assess whether it is safe in terms of ship's stability. Therefore the proposed method provides four types of information: motion parameters of targets within a given range, combinations of own course and speed which collide with those targets, combinations of own course and speed which would lead to grounding within a specified time and combinations of own course and speed, which could result in stability-related dynamical threats. Optionally it is also possible to display only manoeuvres compliant with COLREGS. A superposition of these types of data enables a navigator to choose an efficient manoeuvre in a situation when possibilities are limited by weather conditions and actual characteristics of the ship stability.