Welcome
to
Radar Plotting
Objectives
Ability to operate, and to interpret and analyze information
obtained from radar, including the following:
performance including:
Factors affecting performance and accuracy
Setting up and maintaining displays
- Detection of misrepresentation of information,
false echoes, sea return etc., racons and sarts
Objectives ( continued..)
Ability to operate, and to interpret and analyze information
obtained from radar, including the following:
use including
- Range and bearing, course and speed of other
ships, time and distance of closest approach
of crossing, meeting and overtaking ships
- Identification of critical echoes, detecting course and
speed changes of other ships, affect of changes in
own ships course or speed or both.
- Application of the International Regulators for
preventing collisions at sea
- Plotting techniques, relative and true motion concept
- Parallel indexing
Objectives ( continued..)
Ability to operate, and to interpret and analyze information
obtained from radar, including the following:
System performance and accuracy, tracking
capabilities and limitations and processing delays
Use of Operational warnings and system tests
Methods of target acquisition and their limitations
True and relative vectors, graphic representation of
target information and danger areas
Deriving and analyzing information, critical echoes,
exclusion areas and trial manoeuvres
Radar Plotting:
• While plotting on a chart please ensure that the scale
remains constant.
• The Interval used for taking the observations is crucial
to ensure that the plot can be developed into a readily
understandable and worked triangle.
•The Interval is again dependent upon the range scale in
use and the speed of the two ships and also on the
approach speed between the ships.
•Use the Interval in such a manner so that the time may
be converted easily into one place of decimal. (6m = .1 hr.)
(speed. 13.5 knots Interval 6m distance traveled 1.35NM)
•North up plotting is generally considered more suitable
since it compares well with the chart
Radar Plotting: O Own Co. 000 T
A W
N
C
CPA
The following conventions for naming the triangle is
used:
O - 1st. Observation, position of target on Plotting sheet
A - Last observation, position of target on Plotting sheet
W- Position of Own vessel, after applying own course and
speed, heading towards ‘O’ ( in other words reverse the
own course and draw from ‘O’)
Radar Plotting: O Own Co. 000 T
A W
N
C
CPA
Join all the points and name the triangle OAW
The arrowheads are again a conventional symbol.
For line WO the arrowhead always is in the direction of
WO and not OW
Similarly the arrowhead is in direction WA and not AW
Also the Approach line has the arrowhead as OA and not
AO
Radar Plotting:
Own Co. 000 T
O
A W
N
C
CPA:
This is the closest point of approach between the two vessels,
however this should not be confused with bow pass.
At CPA, the distance between the vessels is the least. This
remains constant so lo9ng as the vessels do not make any
alterations to course and or speed.
Radar Plotting:
Own Co. 000 T
O
A W
N
C
TCPA:
This is the Time that will elapse between the time of the last
observation position and the time when the vessels will be
least distance away.
Radar Plotting:
Own Co. 000 T
O
A W
X
N
C Tgts.Co.
Aspect:
Is the bearing of Own vessel from the target vessel.
Represented in the figure by CAX.
Aspect is conventionally given not as three figure notation but
as Relative bearings, that is Red or Green
Radar Plotting:
Double click on the Symbol above to view the Plotting
sequence animation.
Radar Plotting: O O’ Own Co. after
alteration
A W
N
C
CPA
For any additional points so marked after any alteration
of course and or speed the new O or A or W or all are
marked thus O’ A’ W’ and if more then O’’ A’’ W’’
Radar Plotting: O O’ After alteration
of course
A W
N
C
CPA
Note on the figure, that due to a decision to alter course
by Own vessel, a new triangle was not formed, but the
existing triangle was amended.
This will hold true even if there is a performance delay.
Radar Plotting: O O’ After alteration
of course
A W
A’ New CPA
N
CC
Note that the New approach line
Y A’Y’ (blue), is actually from A’, but
is plotted as similar, parallel to AO’
Y’
Performance Delay:
Is the time taken by the vessel, to respond to a command.
For example: Command alteration of course by 30 degree,
actually takes effect after a certain duration of time.
This duration of time is again dependent on various
factors.
Radar Plotting: O After reduction
O’ of speed
A W
A’
Y’ Y
New CPA
Performance Delay:
Is the time taken by the vessel, to respond to a command.
For example: Command reduction of speed to half of
original speed, actually takes effect after a certain
duration of time.
This duration of time is again dependent on various
factors.
Radar Plotting: O After reduction
O’ of speed
A W
A’
Y’ Y
New CPA
Performance Delay:
This depends on:
• Ship type
• Loading conditions (Loaded or in ballast)
• Condition of the sea
• Stability of the ship
• The magnitude of the action ordered
Radar Plotting: O After reduction
O’ of speed
A W
A’
Y’ Y
New CPA
Head Reach:
This is the distance that a ship travels after the ME has
been stopped. This is generally given as distance traveled
in a fixed period of time.
