Collision diameter for maritime accidents considering the drifting of vessels

In the maritime literature, collision diameter is the distance between the ship centers for physical contact. The collision diameter, as described in the literature neglects the drifting of the ship from its course. External forces such as the cross-wind and/or cross-current may cause drifting of the ship which can be observed as a differentiation between course over ground (COG) and heading (HDG). In this study, a detailed discussion of maritime encounters based on molecular collision theory, and the lacking points at the existing approaches are discussed. Calculations are modified to obtain a more realistic collision diameter. The novelty of the developed collision diameter is the usage of HDG and COG in the collision diameter equation which accounts for the drifting due to external forces. The developed collision diameter is applied to the Strait of Istanbul where fluctuating water currents are continuously affecting the ships during their navigation. The results are compared with the classical collision diameter approach. The variation in the collision diameter values compared to the standard approach reaches up to 71%. Maximum improvement is observed in the crossing collisions, whereas the head-on and takeover collisions are also affected due to relative drifting of the ships.