User's Manual

5.1 PREPARATION

5─4

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Basic Concept of Collision Avoidance

There are two aspects in collision avoidance: collision prediction and avoidance. Collision prediction is to

predict that two or more vessels will happen to occupy the same point at the same time, while collision

avoidance is to maneuver vessels not to occupy the same point at the same time.

In practical operation of vessels, a spot of collision has to be deemed to be a single point but a closed zone. This

closed zone is conceptually defined as a CPA (Closest Point of Approach). In collision prediction, the time to be

taken until a ship reaches the CPA is defined as a TCPA (Time to CPA).

Fig. 5-2 shows a diagram caked “Collision Triangle”.

Fig. 5-2 Collision Triangle