JRC JMA-3400 Series Instruction Manual page 151

Chapter 5 VARIOUS FUNCTIONS
Marine Accidents and Collisions
Among marine accidents, collision accidents have been highlighted as the tonnages and speeds of ships
become higher along with the increase in traffic at sea.
If a tanker carrying dangerous articles such as crude oil collides with any other vessel, then not only the
vessels involved with the accident but other vessels in the vicinity, port facilities, inhabitants in the coastal
area as well as marine resources may also suffer immeasurable damages and troubles.
Collision accidents have a high percentage of the marine accidents that have occurred in recent years. To
cope with these problems, any effective measures are needed and some equipment to achieve collision
avoidance requirements have been developed at rapid strides.
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. 5-24-2 shows a diagram called "Collision Triangle".
Fig. 5-24-2 Collision Triangle
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