29
1.2 Description of AIS marks
There are four types of marks and the functions are as followings.
⑴
: Mark of not moving status
⑵
: Mark of moving status
⑶
: Mark in case of selecting a ship
⑷
: Mark of dangerous status
The meaning of the marks are as followings.
COG/SOG : Bearing of speed, route
Heading : Heading bearing of ship
Direction of turn : Rotate bearing of ship
In case of marking a dangerous ship, you should distinguish in accordance with CPA/TCPA
and the definition of CPA/TCPA is as followings.
CPA/TCPA : CPA(Closest Point to Approach) means the closest point to approach own
vessel and target vessel. And TCPA means time to reach to CPA.
t
3
t
3
t
2
t
2
t
1
t
1
Target
Target
Target
Target
10 knot
10 knot
10 knot
10 knot
O wn
O wn
O wn
O wn
5 knot
5 knot
5 knot
5 knot
While own vessel moves at 5 knot speed and a target vessel moves at 10 knot speed on
the picture above, we are able to know the distance between own vessel and target vessel
in accordance with each time. At the time
t1
,
t2
,
t3
, …,
tn,,
If we solve the distance between
each point, the distance will be the closest point at
t3.
And, the closest point is CPA and the
time to reach at CPA,
t3,
isTCAP.
