radar plotting 3

CANADIAN COAST GUARD AUXILIARY - PACIFIC

RADAR PLOTTING3


2008


End On Situation


Own vessel 050° 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.

358º R x 2.5 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.

359ºR x 0.77 nautical miles

Mark as “A”

Mark time of 1206

12:06 A

12:00 O



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

12:00 O



6 minute plot

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

12:06 A

12:00 O



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).

12:06 A

12:00 O



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.

12:06 A

12:00 O



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

12:00 O



6 minute plot

(7a) Connect “W” with “A”. “W” to “A” represents target course and distance travelled in the plot interval.

174°R @0.75 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 (0.75 nm)

12:06 A

W

12:00 O



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.

7.5 knots

12:06 A

W

12:00 O



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 very close to starboard - scraping the tube.

12:06 A

W

12:00 O



6 minute plot

(9) The Time to Closest Point of Approach (TCPA) is at the tangent point. OA is 6 minutes.

A to TCPA works out at 2.5 minutes = 12:08:30

12:06 A

W

12:00 O

TCPA


Results

In this case, providing neither you nor the target vessel alter course or speed:

• the target vessel is proceeding at 050° + 174° = 224°C at 7.5 knots

• CPA is at 12:08:30 with a collision


Results – Clear Visibility

• In clear visibility, you are to assume you in an end on situation and therefore must take action to avoid collision. Whilst the other could be taken as a crossing vessel, it is safer to assume an end on situation.

• There is a risk of collision, and therefore you must make a bold alteration to starboard.

• The other vessel should do likewise.


Results – Restricted Visibility

• In restricted visibility, you are required to take action.

• As in clear weather, a broad alteration of course to starboard is the best action, carefully monitoring the actions of the other vessel.

• A 90 degree starboard alteration would be best in this case.


End On Situation


End On 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:



6 minute plot

12:06 A

12:00 O

In this case stopping will only gain you thinking time, but does not prevent a close quarters situation.

You will need to make a 90° alteration of course to starboard and increase speed to comply with rule 14.

You can see immediately he is doing 224°C at 7.5 knots

radar plotting 3

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