RADAR PLOTTING
2
2008
CANADIAN
CANADIANCOAST
COASTGUARD
GUARDAUXILIARY
AUXILIARY- -PACIFIC
PACIFIC
Overtaking Situation
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 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°
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(2) Mark the first radar
bearing and range of the
target.
12:00 O
323º R x 1.8 nautical miles.
All bearings are R as they
are relative to your vessel’s
head.
Mark as "O“
Mark time of 1200
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(3) After 6 minutes mark the
second radar bearing and
range of the target.
12:00 O
12:06 A
309ºR x 0.65 nautical miles
Mark as “A”
Mark time of 1206
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 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
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(5) Transfer your course line
to "O" and pull the line down
the sheet
12:00 O
12:06 A
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 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
(20 knots).
12:00 O
12:06 A
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(6b) Move the dividers at this
setting, and place right point
on the plot interval (6
minutes)
12:00 O
The number under the left
point of the dividers will
indicate the distance gone in
the plot interval. (2 nautical
miles).
W
12:06 A
6 min @ 20 knots = 2.0nm.
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(6c) Lay down 2 nautical
miles on the plot,on own
course vector from “O”.
12:00 O
12:06 A
Mark bottom end “W”
W
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(7a) Connect “W” with “A”.
“W” to “A” represents target
course and distance travelled
in the plot interval.
030°R @1.18 nautical miles
12:00 O
12:06 A
W
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 (1.18
nm)
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 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.
12:00 O
12:06 A
W
11.8 knots
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 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)
12:00 O
12:06 A
W
In this case 0.25 nautical
miles to port
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
(9) The Time to Closest
point of Approach (TCPA) is
at the tangent point. OA is 6
minutes.
12:00 O
12:06 A
TCPA
A to TCPA works out at 2.5
minutes = 12:08:30
W
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Results
In this case, providing neither you nor the target
vessel alter course or speed:
• the target vessel is proceeding at 270° + 030°
= 300°C at 11.8 knots
• CPA is at 12:08:30 at a distance of 0.25nm to
port
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Results – Clear Visibility
• In clear visibility, you are the overtaking
vessel and therefore the give way vessel.
• You will pass clear, but not exhibiting the best
seamanship.
• If a risk of collision was existing, you should
have altered course to port early, and passed
under her stern
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Results – Restricted Visibility
• In restricted visibility, you are still the
overtaking vessel and therefore the give way
vessel.
• You will pass clear, but not exhibiting the best
seamanship. At this stage, a big round turn to
starboard will resolve the situation.
• If a risk of collision was existing, you should
have altered course to port early, (under Rule
19 d.i) and passed under her stern.
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Overtaking Situation
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Overtaking Situation
• If however at 1206 you acknowledge the
other vessel is on nearly a steady bearing,
you can stop and assess the situation.
• The plot will then change to:
CANADIAN COAST GUARD AUXILIARY - PACIFIC
Own vessel 270° at 20 knots
6 minute plot
The other vessel’s plot will
then move across in front of
you, resolving the situation,
clarifying you are overtaking.
12:00 O
12:06 A
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 300°C at 11.8 knots
CANADIAN COAST GUARD AUXILIARY - PACIFIC