User's Manual

Chapter 2
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OPERATIONS
2.15
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SETTING TT/AIS
2-121
2
INSTRUCTION MANUAL
 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. 2.15-2 shows a diagram called "Collision
Triangle".
Fig. 2.15-2 Collision Triangle
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