1. RADAR PLOTTING 1
2008
CANADIAN COAST GUARD AUXILIARY - PACIFIC

2. Crossing Situation

3. Own vessel 000° at 10 knots
6 minute plot
(1) Find the course you are going, and draw a line for your course
In the case of heads up , mark 000°

4. (2) Mark the first radar bearing and range of the target.
Own vessel 000° at 10 knots
6 minute plot
12:00 O
(2) Mark the first radar bearing and range of the target.
045º R x 2.4 nautical miles.
All bearings are R as they are relative to your vessel’s head.
Mark as "O“
Mark time of 1200

5. Own vessel 000° at 10 knots 6 minute plot
(3) After 6 minutes mark the second radar bearing and range of the target.
044ºR x 1.00 nautical miles
Mark as “A”
Mark time of 1206
12:06 A

6. Own vessel 000° at 10 knots 6 minute plot
(4) From "O" draw a line through "A" and carry the line well past the centre line on the screen
12:06 A

7. (5) Transfer your course line to "O" and pull the line down the sheet
Own vessel 000° at 10 knots
6 minute plot
12:00 O
(5) Transfer your course line to "O" and pull the line down the sheet
12:06 A

8. (6a) Calculate own vessel distance in plot interval.
Own vessel 000° at 10 knots
6 minute plot
12:00 O
(6a) Calculate own vessel distance in plot interval.
To use calculator scale, place right point of divider on 60 (right end of scale) and left point on own vessel speed (10 knots).
12:06 A

9. Own vessel 000° at 10 knots 6 minute plot
(6b) Move the dividers at this setting, and place right point on the plot interval (6 minutes)
The number under the left point of the dividers will indicate the distance gone in the plot interval. (1 nautical mile).
6 10 knots = 1.0nm.
12:06 A

10. Own vessel 000° at 10 knots 6 minute plot
(6c) Lay down 1 nautical mile on the plot,on own course vector from “O”.
Mark bottom end “W”
12:06 A W

11. Own vessel 000° at 10 knots 6 minute plot
(7a) Connect “W” with “A”. “W” to “A” represents target course and distance traveled in the plot interval.
nautical miles
To convert this into speed, place right point of dividers on plot interval (6 minutes) and the left point on distance travelled in that time (1.00 nm)
12:06 A W

12. Own vessel 000° at 10 knots 6 minute plot
(7b) Move dividers so that right point is on 60 (right hand end of scale).
The reading under the left point of the dividers will be the vessel’s speed in knots.
10.0 knots
12:06 A W

13. In this case 0.0 nautical mile
Own vessel 000° at 10 knots
6 minute plot
12:00 O
(8) Where the line through “O” and “A” passes closest to the centre of the plot is the Closest Point of Approach (CPA)
In this case 0.0 nautical mile
12:06 A W
CPA

14. A to TCPA works out at 3.8 minutes = 12:09:48
Own vessel 000° at 10 knots
6 minute plot
12:00 O
(9) The Time to Closest point of Approach (TCPA) is at the tangent point. OA is 6 minutes.
A to TCPA works out at 3.8 minutes = 12:09:48
12:06 A W
TCPA

15. Results
In this case, providing neither you nor the target vessel alter course or speed:
the target vessel is proceeding at 000° + 267° = 267°C at 10.0 knots
CPA is at 12:09:48 at a with a collision.

16. Results – Clear Visibility
In clear visibility, you are in a crossing situation with other vessel on your starboard side, and therefore you are the give way vessel.
There is risk of collision. You MUST take action which should involve a bold alteration to starboard, and/or a reduction in speed, until the other vessel is past and clear.

17. Results – Restricted Visibility
In restricted visibility, you are still the crossing vessel and the give way vessel, and a risk of collision does exist.
You MUST take action to keep clear of the other vessel. A large alteration of course to starboard, and / or stopping your vessel will resolve the situation.
See Rule 19 d.i of the Collision Regulations

18. Crossing Situation

19. Crossing Situation
If however at 1206 you acknowledge the other vessel is on a steady bearing, you can stop and assess the situation.
The plot will then change to:

20. You can see immediately he is doing 267°C at 10 knots
Own vessel 000° at 10 knots
6 minute plot
12:00 O
The other vessel’s plot will then move across in front of you, resolving the situation.
You have made a substantial alteration in speed which will be readily visible to him, whether he is observing you visually or by radar.
You can see immediately he is doing 267°C at 10 knots
12:06 A