Provides GPS-based data including SOG (Speed Over Ground) and COG (Course Over Ground). 4. Calculation Methodology
The is the estimated position where the distance between two ships (the "own ship" and a "target vessel") reaches its absolute minimum. It is the primary metric used by Watchkeeping Officers to assess the Risk of Collision (ROC) . If the CPA is too small, a collision is possible, requiring immediate maneuvering according to COLREGs . 2. Core Parameters The method relies on two primary mathematical outputs:
Incorporating Rate of Turn (ROT) and Change of Speed (COS) into AIS-based predictions for more accurate results during maneuvers. Ocean CPA method.pdf
💡 While the basic CPA method provides a "point-in-time" safety check, modern ocean navigation requires combining CPA with Ship Domain models to ensure reliable collision avoidance in busy shipping lanes. If you'd like, I can provide: The specific mathematical formulas for DCPA and TCPA A summary of COLREG rules related to collision avoidance
The CPA is traditionally calculated using vector geometry. Determine Relative Velocity ( Vrcap V sub r Provides GPS-based data including SOG (Speed Over Ground)
): The vector difference between the own ship’s velocity and the target's velocity.
Calculated by dividing the relative distance projection by the relative speed. It is the primary metric used by Watchkeeping
Defining a "safe zone" around a ship rather than a single point.