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5.1 Preparation
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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
True vector of
Tar
et vessel
Target
vessel
TCPA ring
(Time to CPA)
Own ship
CPA ring
True vector of own
shi
Relative vector
Collision triangle
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