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1. 1. © Grunt Productions 2007 RADAR PLOTTINGRADAR PLOTTING A brief by Lance GrindleyA brief by Lance Grindley
2. 2. © Grunt Productions 2007 Crossing SituationCrossing Situation
3. 3. © Grunt Productions 2007 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. 4. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot (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 12:00 O
5. 5. © Grunt Productions 2007 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 12:00 O 12:06 A
6. 6. © Grunt Productions 2007 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 12:00 O 12:06 A
7. 7. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot (5) Transfer your course line to "O" and pull the line down the sheet 12:00 O 12:06 A
8. 8. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot (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). 12:00 O 12:06 A
9. 9. © Grunt Productions 2007 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 min @ 10 knots = 1.0nm. 12:00 O 12:06 A
10. 10. © Grunt Productions 2007 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” 12:00 O 12:06 A W
11. 11. © Grunt Productions 2007 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. 267°R @1.00 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) 12:00 O 12:06 A W
12. 12. © Grunt Productions 2007 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 12:00 O 12:06 A W
13. 13. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot (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 12:00 O 12:06 A W CPA
14. 14. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot 12:00 O 12:06 A W (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 TCPA
15. 15. © Grunt Productions 2007 ResultsResults In this case, providing neither you nor theIn this case, providing neither you nor the target vessel alter course or speed:target vessel alter course or speed:  the target vessel is proceeding at 000° +the target vessel is proceeding at 000° + 267° = 267°C at 10.0 knots267° = 267°C at 10.0 knots  CPA is at 12:09:48 at a with a collision.CPA is at 12:09:48 at a with a collision.
16. 16. © Grunt Productions 2007 Results – Clear VisibilityResults – Clear Visibility  In clear visibility, you are in a crossingIn clear visibility, you are in a crossing situation with other vessel on yoursituation with other vessel on your starboard side, and therefore you are thestarboard side, and therefore you are the give way vessel.give way vessel.  There is risk of collision. You MUST takeThere is risk of collision. You MUST take action which should involve a boldaction which should involve a bold alteration to starboard, and/or a reductionalteration to starboard, and/or a reduction in speed, until the other vessel is past andin speed, until the other vessel is past and clear.clear.
17. 17. © Grunt Productions 2007 Crossing SituationCrossing Situation  If however at 1206 you acknowledge theIf however at 1206 you acknowledge the other vessel is on a steady bearing, youother vessel is on a steady bearing, you can stop and assess the situation.can stop and assess the situation.  The plot will then change to:The plot will then change to:
18. 18. © Grunt Productions 2007 Own vessel 000° at 10 knots 6 minute plot 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 12:00 O 12:06 A