Basic Concept Of Collision Avoidance - JRC JMA-9832-SA Instruction Manual

.
1.6 COLLISION AVOIDANCE

......Basic Concept of Collision Avoidance .................................

There are two aspects in collision avoidance: collision prediction and avoidance. Collision prediction is
1
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.1.20 shows a diagram called "Collision Triangle".
TCPA (Time to CPA)
CPA
Target vessel
Collision triangle
Relative vector
Own ship
CPA RING
Fig.1.20 Collision Triangle
1 – 28