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Grunt Productions 2007

RADAR PLOTTINGRADAR PLOTTING

A brief by Lance GrindleyA brief by Lance Grindley


Crossing SituationCrossing Situation


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°



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



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 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



6 minute plot

(5) Transfer your course line to "O" and pull the line down the sheet

12:00 O

12:06 A



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



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



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 AW



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 AW



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 AW



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 AW

CPA



6 minute plot12:00 O

12:06 AW

(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


ResultsResults

In this case, providing neither you nor the In 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.


Results – Clear VisibilityResults – Clear Visibility

In clear visibility, you are in a crossing In clear visibility, you are in a crossing situation with other vessel on your situation with other vessel on your starboard side, and therefore you are the starboard side, and therefore you are the give way vessel.give way vessel.

There is risk of collision. You MUST take There is risk of collision. You MUST take action which should involve a bold action which should involve a bold alteration to starboard, and/or a reduction alteration to starboard, and/or a reduction in speed, until the other vessel is past and in speed, until the other vessel is past and clear.clear.


Crossing SituationCrossing Situation

If however at 1206 you acknowledge the If however at 1206 you acknowledge the other vessel is on a steady bearing, you other 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:



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

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