Operational Use of Radar Guide

NAVIGATION VI
Operational Use of Radar/ARPA

ObjectivesObjectives
 At the end of the grading period, the students will be able
to demonstrates a knowledge and understanding of the
following:
• Fundamental Principle of Radar
• Safe Distance
• Radiation Hazards and Precaution
• Characteristics of Radar Sets and Factors Affecting
Performances
• Factors External to the Radar Set Affecting Detection
• Factors Causing Faulty Interpretation
• Performance Standards Resolution 477(XII)

Fundamental Principle
of Radar
• RADAR- derived from the phrase RADIO
DETECTION AND RANGING.
A short burst of electro magnetic energy
transmitted and hit to an object and then
return, since the velocity of the
propagation is known it would be easy to
calculate because the distance to the
object as long as it can measure time from
which the transmission started until the
echo return.

of Radar
On Board Ship the RADAR has two main tasks:
 To function as an aid to prevent collision, as
with the help of RADAR one can “SEE” in fog
and darkness.

of Radar
On Board Ship the RADAR has two main tasks:
 To assist in navigation, particularly at landfalls
and when navigating in coastal waters.

Characteristics of Radar Sets and Factors
Affecting Performances
RADIO WAVES are Electro magnetic
Waves motion consist of crest and trough.

• Wavelength- is a distance between a
successive crest of waves, electromagnetic
waves of a length between 0.1-30000 mm
are known as radio waves.
• Frequency- are other way of measure of
waves motion, which indicates the number
of crest that pass a fix of initial time.
• Frequency and Wavelength are two terms
closely associated.

LOW FREQUENCY HIGH FREQUENCY
Each type has their advantages and disadvantages. For example
a short wave length is preferred in shipboard radar system
because there Is a relationship between the size of the antenna
and the Horizontal Beam width, the larger width of the scanner
the smaller is the angular beam width for the same wavelength.

LOW FREQUENCY HIGH FREQUENCY
Most marine radar transmit is:
X Band (3 cm) - 9000 MHZ
C Band (5 cm) - 5000 MHZ
S Band (10 cm) - 3000 MHZ

Marine Radar Component
ANTENNA
TRANSCEIVER TRANSMITTER
MAGNETRON
MODULATOR
TRIGGER
POWER
TRANSFORMER
DISPLAY
RECEIVER
MIXER
1ST
AMPLIFIER
EQUALIZER
VIDEO AMPLIFIER
RADAR BLOCK DIAGRAM

RADAR ANTENNA
Transmit and receive in an concentrated
beam and a motor turns the antenna in
rotation, the signal, which are amplified the
signal becomes visible to the operator in
form of a radar picture.

Two types of RADAR ANTENNA:
SLOTTED WAVE GUIDE
TYPE

Two types of RADAR ANTENNA:
PARABOLIC TYPE

RECEIVER
The incoming signal is fed to a series of
amplifier and further to detect or
demodulator for which smoothes the signal,
the main task of the receiver is to amplify
the reflected (incoming echoes) weak
echoes and make them suitable for
transmission to the indicator.

TRANSMITTER
It is the trigger pulses to the modulator and
converted the inputs into a high frequency
oscillation thru magnetron. A high frequency
oscillation are fed via wave guide or into a
coaxial cable to the transmitter/receiver
switch.

DISPLAY
A radar echoes are display in a cathode ray
tube (CRT). Several types of CRT are
utilized like A-SCAN or Short Persistent
Tube, Plan Position Indicator or PPI, Raster
Scan Display.
A-SCAN or short persistent tube, the
strength of an echo derived from its
amplitude.

P.P.I DISPLAY

DISPLAY
PPI is a long persistent tube, the trace is
rotated around in unison with the rotation of
the scanner and echoes previously
recorded are retained during a period of at
least one scanner revolution.

DISPLAY
RASTER SCAN DISPLAY. Normally a
rectangular screen with dimension in the ratio
4:3 consisting of; example 1024 horizontal
lines and 1280 vertical line or picture elements
(pixel)
The radar provides all echoes information in
Cartesian form (i.e. range, bearing). Before the
information can be displayed the information
must be recalculated into X-Y coordinated by a
processor.

RASTER SCAN DISPLAY

DISPLAY
The advantage of raster scan is that, it can
be viewed in daylight without a visor, and
the capacity for the additional graphic
information is almost unlimited compared
with the PPI.
The disadvantage of the raster scan is that
even the best raster scan display available
today, cannot match the resolution of the
old PPI.

Factors External to the Radar Set Affecting
Detection
RADAR SCAN & RADAR SWEEP
Radar Scan- it is a one complete 360
degrees rotation of the antenna (during one
scan normally thousand sweeps are
generated and transmitted)
Radar Sweep- is the transmission of one
radar pulse only.

Detection
PULSE REPETITION FREQUENCY (PRF)
Define as the number of pulses transmitted
per second.
Long pulse is equals to low PRF
Short pulse equals to high PRF
LONG PULSE- means more power and
longer range but less resolution in range.
SHORT PULSE- means a weaker pulse,
less radar range but better resolution in
range.

Detection
RADAR RANGE DEPEND MAINLY IN DIFFERENT
PARAMETERS
Vertical Beam Width
Selected Pulse Length
Height of Antenna
Installation of Antenna
Ship’s Trim

Safe Distance
IMPORTANT RADAR RANGE
PARAMETERS
Antenna Height
Height of the Target
Size of the Target
Target Reflecting Area
Materials of the Target
Shape of the Target
Weather Condition

Safe Distance
FOLLOWING PARAMETERS MUST TAKEN INTO
ACCOUNT:
 Transmitted Peak Power
 Wavelength
 Pulse Length
 Antenna Gain
 Noise Figure
 Number of Pulses Per Scan
 Wave Guide Loss
 Display Parameters

Safe Distance
RANGE DISCRIMINATION
The ability of radar to discriminate
between two small object close together
in the same bearing.
Effecting range discrimination are:
Select Pulse Length
The size of the spot
If possible short pulse and short range should be
selected and focused, brightness carefully adjusted.

Safe Distance
BEARING DISCRIMINATION
The ability of radar to discriminate
between two small object close together
at the same range but different bearing.
Bearing discrimination depends on:
Horizontal Beam Width
The spot size
Correct focusing and brightness setting
will improve the bearing discrimination.

Safe Distance
BEARING AND RANGE DISTORTION
The radar’s possibility to reproduce on area
or a ship correctly and to discriminate
between close lying targets is limited and
varies with different types of radar.
The discriminating ability in range is usually
25-75 meters, however the accuracy is
lower on long range.

Safe Distance
BEARING AND RANGE DISTORTION
The discriminating ability laterally is usually
1-2 degrees.
Radar sets with a wavelength of 3 cm have
a better discriminating ability compared with
the 1 cm wavelength.

Radiation Hazards and
Precaution
MAGNETIC COMPASS
The magnetic compass must have a safe
distance from the radar. Nowadays,
although most ships are equipped with zero
compass, the magnetic compass is still the
master compass on all ships and thus
should be taken good care of.
Normally the safe distance varies between
1 and 5 meters.

Precaution
RADIATION
Marine radar transmits energy of varying
strength in form of short pulses or bursts.
Pulse power can produce biological
changes not obtained with constant wave
transmission. At short distance,
transmission from marine radars may pose
a health hazard, follow the instruction from
the radar manufacturer closely and don’t
take any chances.

Precaution
RADIATION
When working close to a radar antenna,
make sure that a warning signal has been
placed on the radar console. Clearly telling
everybody that no start up should be
attempted before the work on the antenna is
completed or cancelled.

PrecautionRADIATION
Whenever the air humidity is abnormally
high which it is in fog, rain, snow and hale, a
reduction in radar detection range should be
expected.
Some disturbances of radar picture:
Sea
Rain
These disturbances maybe serious so refer to
the radar manual for more details.

Precaution
NORMAL TRANSMISSION OF RADAR
WAVES
 Radar conditions at approximately 10-15% greater
that the distance to the optical horizon said to
have normal transmission of radar waves.
 Generally, normal conditions exist in areas with
cold air masses. The longer the wavelength, the
greater is the tendency to bend round objects.
Hence you can expect the 1 cm radar to have
greater range that the 3 cm radar.

Precaution
SUB-REFRACTION
 When warm, moist air remains over cold water,
the air is cooled from below creating a fog.
Temperature end humidity will increase with
altitude and the radar wave will bend upwards;
decreasing the radar range is called
sub-refraction.

Precaution
DUCTING
 With conditions of light wind and low clouds over
cold water we often get a condition called
“ducting”. That is, when radar beam is reflected
several times between the fog and sea surface.
The radar range can be increased considerably.
 Ducting can be expected to take place when
temperature inversion exist and the atmosphere is
calm.

Precaution
RADAR BLACKOUT
With conditions of considerable ground fog, we can
get a total radar blackout:
 All radar waves are reflected from the top of the
fog.
 Stationary warm air masses located on top of cold
sea.
 If the height of the fog is less that the height of the
radar antenna, a total reflection of the radar signal
from the top of the fog may take place.

Precaution
SEA CLUTTER
 Sea clutter echoes are caused by reflection of the
radar pulse against the sea waves. The reflection
is specular and conditions for the pulse to return
to the scanner are favorable near the ship. At
longer ranges the beam will be deflected away
from the ship.
 Marine radars are equipped with rejection systems
to minimize the effect of sea clutter. This control is
often named “Anti Clutter Sea” or “STC”.

Precaution
RADAR SHADOW
 As we have seen, the radar waves transmit in a
straight line. A radar coastline echo (or any other
objects) appearance will be determined by the
topography. The radar picture can be quite
different from the map.
 Another important reason for the difference
between sea map and the radar image is the
radar range and bearing discrimination
parameters, i.e. how much the radar “magnifies”
the echo in range and bearing.

Precaution
CENTERING ERRORS
 The sweep center, which on the PPI indicates own
ship, must coincide exactly with the cursor center
of rotation to achieve a correct bearing.
 Another important reason for the difference
between sea map and the radar image is the
radar range and bearing discrimination
parameters, i.e. how much the radar “magnifies”
the echo in range and bearing.

The Use of Radar in Navigation
Interpretation of the Radar Picture
 The radar picture is a plain picture of the ships
surroundings. Only long training and experience
can teach you to interpret the radar picture quickly
and accurately as well as to identify different
targets.
 Use of radar to assist in navigation can be divided
into 3 categories:
 Making Landfall
 Coastal Navigation
 Pilotage

LANDFALL NAVIGATION
Landfall by radar may give surprises.
Always remember: initial radar fixes are
often not reliable at long ranges and when
approaching land the picture may change
completely.

COASTAL NAVIGATION
Coastal navigation requires experience and
vigilance all the time. The range accuracy of
the radar is generally better than the
bearing accuracy. When bearings has to be
taken, choose isolated targets of relative
small size.

PILOTAGE
For navigation in narrow waters, radar is
great device. The navigator must know
radar shadows. Knowledge is essential in
order to distinguish clearly between
stationary and moving objects.

Precaution
RADAR REFLECTORS
 The purpose of radar reflector is to direct as much
as possible of the reflected radar energy back to
the radar antenna, which means stronger echoes
on the PPI.
RADAR BEACONS
 Racon signal appears in PPI and provides bearing
and range of target.

Precaution
THREE MOTION COMPONENTS
 The targets relative course and speed is the targets
motion in relation to own ship during the echoes
movements across the PPI on a relative motion
display.
 The targets true course and speed is the targets true
motion during the period of observation. This
corresponds to the echoes movements across the PPI
on a true motion display.
 The own ships course and speed are your ships true
motion during the period of observation.

Precaution
MULTIPLE ECHOES
 Multiple echoes can be created by reflection between
own ship and an object before the scanner finally
collects its energy. We will see a line of targets on the
same bearing and with equal distance between them.
 True echo is the one closest to own ship. The shapes
of multiple echoes are less defined that that of the
original echo and they are weakening in intensity
outwards. Reduction of gain and clutter will remove
the false echo before the true echo.

Precaution
SIDE ECHOES
 The side lobes cause side echoes. The effect of side
echoes will only be observed at short ranges. Nearby
target are picked up by the side lobes as well as by
the main lobe. Anticlutter will normally remove side
echoes.
 It is impossible to design a scanner without side lobes
although the construction of an aerial affects the
magnitude of side lobes. However, today many slotted
wave guide scanners have almost eliminated the
visual effect of side echoes.

Precaution
BLIND SECTORS
 Antenna not placed at the ships highest point.
Structures above antenna will create blind sector in
radar screen. Objects within these sectors will
normally be invisible in the screen. It is relatively easy
to plot the blind sectors if this is done during the
period with a lot of sea clutter. The blind sectors can
be seen as distinctly dark sectors in the sea clutter
area. Plot each sector on a plotting sheet and place
this so it can easily be seen from the radar observed
position.

Precaution
HEADING MARKER ERRORS
 When the heading marker on the radar screen does
not exactly tally with the ships heading, or in other
words, when the echo from a target straight ahead
does not lie exactly on the heading line, then we have
a heading marker error.
 Heading Marker error may have serious effects on the
radar picture and has been the cause of many
collisions.

Precaution
FALSE ECHOES
 If the radar signal is reflected from objects on board in
such a way that the pulse hits a target, we may
receive a false echo at almost the same distance as to
the real target but on a different bearing. This false
echo will often be located on own ships blind sector.
 The navigator should know exactly where own ships
blinds sectors are located. This is important in order to
take actions to minimize the effect of the blind sectors.

Precaution
RAIN SQUALLS AND SHOWERS
 Rainsqualls and showers appear on the screen as a
wooly mass.
 An intense rainstorm can be detected up to 25 miles
 Thunderstorms give excellent echoes
 Rain and clutter and targets beyond the rain area
will obscure echoes inside the rainstorm

Precaution
WEATHER CONDITION
 During weather conditions including heavy rain, thunderstorms
etc., the S-band is a better choice than X-band radar.
 False echoes and disturbances
 Own ships antenna receives signals from another radar
 Fan shaped broken lines emanating from the center of the
screen
 Most radar equipments contain radar interference rejection
circuits to eliminate this disturbance
 False echoes and disturbances on the radar screen may
have many different appearances and causes. Some faults
can affect the accuracy, so whenever disturbances are
observed be especially aware of this possibility.

Precaution
SYMBOLS FOR RADAR
CONTROL
1. Radar Off
2. Radar On
3. Radar Stand By
4. Aerial Rotating
5. North-up Presentation
6. Head-up Presentation
7. Heading Marker Alignment
8. Range Selector
9. Short Pulse
10.Long Pulse
11.Gain
SYMBOLS FOR RADAR
CONTROL
12.Tuning
13.Anti Clutter Rain Minimum
14.Anti Clutter Rain Maximum
15.Anti Clutter Sea Minimum
16.Anti Clutter Sea Maximum
17.Scale Illumination
18.Display Brilliance
19.Range Rings Brilliance
20.Variable Range Marker
21.Bearing Marker
22.Transmitted Power Monitor

Precaution
SYMBOLS FOR RADAR CONTROL

Precaution
SYMBOLS FOR RADAR CONTROL
 There are seven main controls that determine the
performance of the radar:
• standby/transmit
• brilliance
• gain
• tuning
• range
• anti sea clutter control (STC)
• anti rain clutter control (FTC)

Symbols For Radar Control
Standby/Transmit
 The standby/transmit switch usually has three positions
labelled ‘off’, ‘standby’, and ‘transmit’. Turning the switch to
standby will activate the radar set, however it doesn’t come
on immediately as the magnetron needs a few minutes to
warm up before it can transmit. The radar will have some
form of visual signal to indicate when this period is expired.
The radar can then be switched to ‘transmit’ and on some
sets a short or long pulse can be selected at this time,
normally long pulse would be selected. A long pulse will be
more likely to show an echo from a weak target or a target
at a longer range. A short pulse will achieve better
definition on short ranges.

Standby/Transmit
 As well as its main function of giving the magnetron time to
warm up, in ‘standby’ mode the scanner is not rotating (on
most sets) and is a way of conserving power and
prolonging the life of the magnetron while keeping the set
ready for immediate use. It is a good practice at sea to
leave the radar on ‘standby’ at all times as this will prevent
condensation forming inside the radar set.

Brilliance
 The brilliance control on an analogue radar controls the
brightness of the rotating trace and will also affects the
brightness of the displayed echo so it needs to be adjusted
so that the trace itself is just visible, to give a good contrast
between echo and background.
 On a raster scan display the brilliance control regulates the
brightness of the picture, making it bright enough for
daylight viewing or dim enough so as not to impair the
operators night vision.

Gain
 The gain control may appear to have a similar function as the
brilliance control in that operating it makes the picture brighter or
darker. This similarity however, is only superficial as the gain
control has a completely separate function and it is important
not to confuse the two.
 The gain control affects the receiver and not the display as the
brilliance does. Turning up the gain will increase the
amplification of the incoming signal, making weak echoes look
stronger, but confusing the display with background speckle or
noise, similar to the background crackling of an ordinary radio.
Turning down the gain will reduce the sensitivity of the receiver
and reduce the speckle but care must be exercised that this is
not overdone as weak or distant echoes may be lost

Tuning
 The tuning control can be compared to the tuning control
of an ordinary radio, in that it tunes the receiver to the
frequency of the transmitter. Poor tuning adjustment may
not be easily recognised on the screen. Tuning slightly out
will eliminate some very weak echoes, but still produce a
clear picture of the stronger ones. Hence the importance of
frequent fine tuning of the set.

Range
 The range control regulates the range at which the set
operates. It simply changes the size of the area on the
display and hence the scale. You would change the range
of the radar just as you would change charts for passage
planning or close-in piloting. The choice of range would
depend on what you are using the radar for, and your
locality. For coastal navigation you might select a range of
6 or 12 miles so that appropriate coastal features will be
displayed, for collision avoidance a range of 12 miles or 24
miles may be appropriate, for pilotage into a confined
anchorage a range of ½ a mile may be needed.

Sea Clutter Control (STC)
 The radar beam will bounce echoes off the sea around the ship,
particularly if the weather is a little rough. This result will be a
bright sunburst pattern in the middle of the screen which will be
more pronounced in the upwind direction. You could reduce this
by turning down the gain, the down side to that solution
however, is that the echoes of more distant targets will be lost
as well.
 The solution is the sea clutter control. It works by reducing the
receiver gain for a few microseconds after each pulse is
transmitted, then gradually restores it to its former level. It works
very well, but its use requires care. Too much sea clutter control
will result in the loss of close range targets. At sea the sea
clutter control must be continually monitored and adjusted.

Rain Clutter Control (RTC)
 The rain clutter control will reduce the interference on the
screen due to the rain and increase the chance of seeing
targets within rain showers. The effect on returning echoes
from rain on the screen is usually no more than a
transparent smear, looking a little like cotton wool, but it
can be dense enough to conceal other echoes within the
shower. In a tropical downpour however, the rain can
completely block out all echoes, at times requiring the
operator to stop the vessel.

Rain Clutter Control (RTC)
 The rain clutter control works by making use of the fact
that the returning echo from rain is different from the
returning echo of a solid object. The returning echo from
rain is much longer and very much less dense than the
echo from a solid object. The rain clutter circuitry works by
passing on to the receiver only the leading edge of a
returning echo. This does not affect the returning echo
from a solid object like a ship, but drawn out, weak
returning echoes from the rain however, will be weakened
considerably.

Setting Up Radar Display
START UP SEQUENCE
 Radar ON/OFF
 Radar Standby
 Scanner ON/OFF

CHOICE OF RADAR PRESENTATION
 Many factors may influence a navigator’s choice of radar
presentation. Availability of equipment and own experience will
naturally be deciding factors, but it is important that navigator is
aware that he is not completely free in his selection of radar
presentations.
 A navigator on a ship equipped with True Motion Radar,
operating in an area with dense traffic is obliged to utilize True
Motion radar presentation in order to avoid additional problems
in a possible collision case. The reason for this is that True
Motion presentation is considered to be, and is the best choice
under such conditions. Most navigators who use their equipment
correctly will soon obtain the needed experience to choose the
presentation that provides the simplest and most accurate
information at anytime.

MEASUREMENT OF RANGE
 The range accuracy of radar is generally high. Range can be
measured on radar with reference to fixed range rings equally
spaced around own ships position on the radar screen. For
more accurate measurement of range, most modern radars
provide a variable range ring that can be positioned in any range
on the screen.
 The Variable range ring should regularly be checked for
accuracy against the fixed range rings, which are normally most
stable. With a variable range ring more accurate measurements
can be taken. Fixed range rings can be used when the need for
high accuracy is not important.

BEARING ACCURACY
 The bearing accuracy of massive radars is normally not so high
 Beam with distortion, which can be partly eliminated by
reduction in gain.
 Heading marker error, which can be determined by various
methods
 Centering error, which can easily be corrected
 Error due to yawing of own ship
 Error due to parallax when viewing the display
 Always read and follow the radar manufacturer recommendations
for use and maintenance of the radar equipment. This will save
you time and money and ensure proper use of equipment.

Marine Radar Performance
Specification
Performance Standards for Radar Equipm

 At the end of the grading period, the students will
be able to demonstrates a knowledge and
understanding of the following:
• Construct the relative motion triangle
• Determine course, speed and aspect of other
ships
• Determine the closest point of approach (CPA)
and time to closest approach (TCPA)
• Determine the effect of course and speed changes
• Report Radar Plot data

PLOTTING
Purpose of Plotting
1. It can show whether danger of collision exists, how close
will pass the target and how much time there is left
before this will take place.
2. Approximate determination of the course and speed of
the other vessel, so that sensible avoiding action can be
taken when needed.
 Manual plotting in connection to radar means to mark
one or more echoes within a specific time interval and
thus decide the target’s movement in relation to own
ship.
 The objective of plotting is to obtain the clearest possible
picture of the situation.

PLOTTING
The Plotting Process
 Detection- recognition of the presence of the
target.
 Selection- choosing of target requiring closer
observation
 Tracking- the process of observing changes in
target position
 Plotting- the whole process of detection,
selection, tracking, calculation of targets
parameter

PLOTTING
Target Aspect
 The aspect is defined as the angle of view
however, in connection with plotting we will use
the term “Calculated Aspect” in order to
distinguish between the two.
 It can be defined as the angle between the target
ships heading and bearing to own ship, as seen
from the target ship.
 In connection with plotting and use of radar and
ARPA, we had better define what we receive
from these systems as calculated aspect.

PLOTTING
Target Aspect
Target Ship
Aspect Red 40
Own Ship
Aspect B measured from dead to a head to 180
degrees on either side of the ship.

PLOTTING
Relative Aspect
 Relative speed is defined as the target speed
relative to own ship, as deducted from a number
of measurements of its range and bearing on the
radar, expressed as an angular distance from
own ships heading.

PLOTTING
Plotting Triangle
 Knowledge of the speed triangle is essential for
understanding the principles used in plotting.
R
E
M
R - M = Echo Line/Relative Track
E – M = Target Ship Course and Speed
E – R = Own Ship Course and Speed

PLOTTING
Heading
 Defined as the direction in which the bow of a
vessel is pointing, expressed as an angular
distance from north.
North
Heading 45
45 degrees

PLOTTING
Relative Bearing
 If the relative bearing of an approaching target
remains the same over time, collision danger is
observed.
Relative Bearing
of Target 030 degrees
Own Ship Heading

PLOTTING
True Bearing
 On merchant ships, true bearing is mainly used
for position fixing.
North
True Bearing 300 degrees

PLOTTING
Bearing
 On a ship bearing can be relative or true in
connection with traffic surveillance, relative
bearing are often used.
True North
Relative Bearing
Ship’s Heading
015 degrees
Relative Bearing

PLOTTING
CPA (Closest Point on Approach)
 CPA must not be mixed with the point where the
target crosses own ship’s heading, often referred
to as BCP (Bow Crossing Point)
Bow Crossing Point
CPA
TCPA

PLOTTING
TCPA (Time Closest Point on Approach)
 TCPA is the time estimated as measured along
the echo line form its present position to the
closest point on approach.
Bow Crossing Point
CPA
TCPA

PLOTTING
Maneuvering Board
 Plotting can be done with head up or north up
however, regardless of selected radar presentation
it is advantageous to plot with north up.
True Plotting
 Gives a natural and easily understood picture of the
course of events.
 Can be done directly in the chart if the scale is
large enough to give a clear picture.
 Gives an easily understood picture of the situation

PLOTTING
Relative Plotting
 Own ship is considered a fixed point. Plotting
must be done with high accuracy and great care.
 Heavy traffic can make manual plotting
impossible.

PLOTTING
Electronic Plotting
 Today many modern radars are equipped with
an electronic plotting feature. Used together with
EBL (Electronic Bearing Lines) is very good tool
in the hands of a qualified navigator. These radar
features make plotting direct on the radar display
very convenient and replace the need for
reflection plotter or plotting sheets.

PLOTTING
Errors in Manual Plotting
 Even small errors in one or several of these
parameters can cause large and dangerous
errors in the plot calculations. Always check
these parameters as thoroughly as possible in
order to reduce the possibilities for “nasty
surprises” during manual plotting work.

PLOTTING
Sources of Errors in Manual Plotting
 Bearing Error
 Distance Error
 Error in timing between plots
 Error in speed
 Gyro Error
 Relative Speed
 Maneuvering of own vessel
 Unstable steering, yawing, etc.

Collision Danger
 The usual method of deciding whether a collision
danger is present is taking several bearings. This
is time consuming, and it requires that many
bearings have to be taken.
 A dangerous situation can quickly emerged by
taking a few inaccurate bearings from a
comparatively long distance and then “forgetting”
the target if the CPA is considered large enough.

Errors in Distance Measurement
 An error in distance measurement, as in bearing
error, can produce grave results when judging
the traffic situation.
Errors in Timing
 A timing error between two plots will result in
calculation of incorrect target course, speed and
time to CPA.

Errors in Speed
 An error on speed causes incorrect calculation in
the same manner as error timing. However, we
must remember that in all plotting where we wish
a picture of aspect, own vessels speed through
the water must be utilized. Never make
corrections due to current or drift. In connection
with plotting, speed through water should be
used.

Gyro Error
 Make it a habit to always correct the gyro for
known gyro error target with low speed.
Factors That Affects Manual Plotting
 Unstable Steering
 Maneuvering of Own Ship
 The Technical Exactness of the Equipment
 Rough Weather Conditions
 Target Relative Speed
 The Navigator’s Experience and Lack of Plotting Practice

VHF (Very High Frequency)
Communication
Importance of VHF Communication
 A way to make ones intentions clear to another
vessel.
 To arrive at an unambiguous decision about
avoiding tactics.
 Broadcasting a general information report to
ships in the vicinity.
 Use of VHF is not explicitly advocated in the
rules, but implicitly (“by all available means”) its
use is recommended.

Communication
VHF Communication Report Content
 Time
 Position
 Course
 Speed
 Maneuvers

Communication
Three Basic Steps to Remember in Using VHF:
 Identification (Own ship name, call sign, type)
 Ascertainment of Movements and Intensions
(time, position, course, speed, etc.)
 Disengagement (indicating both vessels have
recognized the action completed)
Sea speak is the official maritime language initiated by
Captain F.F. Weeks and later adapted by IMO. The
center principle of Sea speak is that receiver should be
alerted to the type of message that follows, at the
beginning of the message.

Communication
Sea Speak Type of Message
 Question- indicates that the following message
is of interrogative character.
 Answer- indicates that the following message is
the reply to previous question
 Request- indicates that the content of the
following message is asking for action from
others with respect to the ship.
 Information- indicates that the following
message is restricted to observed facts.

Communication
Sea Speak Components
 Intention- indicates that the following informs
other about immediate action to be taken.
 Warning- indicates that the following message
informs other traffic participants about danger.
 Advice- indicates that the following message
implies the intention of the sender to influence
the recipient by a recommendation.
 Instruction- indicates that the following
message implies the intention of the sender to
influence the recipient by regulation.

Relative Radar Plotting Symbols
 Symbols are signs, letters, or abbreviations used
to replace words. They are used in mathematics
and certain sciences to good advantage by
reducing the amount of space required
explaining a thing. Since symbols take the place
of words and, they form a language of their own
her here is a list that is used in Radar Plotting.

 CPA - Closest Point of Approach.
 DRM - Direction of relative movement
 e - point of origin of the own ship
 e-m - Contact's vector
 e-r - Own ship's initial vector
 e-r' - Own ship's final
 OC - Own ship's initial course.
 m - The head of the relative motion vector (r-m)
also the head of the contact's vector (e-m).

 RML - Relative Motion Line.
 SRM - Speed of Relative Movement.
 TCPA- time closest point of approach
 NCPA- new closest point of approach
 ST- actual target’s true speed
 CT- true course of target
 mx- point of execution
 AC- collision avoidance course
 AS- collision avoidance speed
 ROCS- resume ownership course and speed

 NRML - New Relative Motion Line the Relative
Motion Line after own ship has maneuvered.
 r - The head of own ship vector (e-r).
 r-m - The relative motion vector.
 M1 - First plotted position of contact

 At the end of the grading period, the students will
be able to demonstrates a knowledge and
understanding of the following:
• Principal ARPA System
• ARPA system display characteristics
• Methods of Displaying Information
• IMO performance standards for ARPA

Principal ARPA System
What is ARPA?
 An abbreviation for Automatic Radar Plotting
Aids. Basically an ARPA is a computerized radar
plotting system, which can perform radar plotting
manually or automatically according to operator’s
choice.
 When it works properly, ARPA is a fantastic tool in
the hands of a qualified navigator with proper
training. One prime requirement for all users of
ARPA is to have good knowledge of the principle of
manual plotting in order to understand the
information given by the ARPA.

What is ARPA?
 An ARPA assesses the risk of collision, and enables
operator to see proposed maneuvers by own ship. While
many different models of ARPAs are available on the
market, the following functions are usually provided:
1. True or relative motion radar presentation.
2. Automatic acquisition of targets plus manual acquisition.
3. Digital read-out of acquired targets which provides course,
speed, range,bearing, closest point of approach (CPA, and
time to CPA (TCPA).
4. The ability to display collision assessment information
directly on the PPI, using vectors (true or relative) or a
graphical Predicted Area of Danger (PAD) display.

What is ARPA?
 An ARPA assesses the risk of collision, and enables
operator to see proposed maneuvers by own ship. While
many different models of ARPAs are available on the
market, the following functions are usually provided:
5. The ability to perform trial maneuvers, including course
changes, speed changes, and combined course/speed
changes.
6. Automatic ground stabilization for navigation purposes.
ARPA processes radar information much more rapidly than
conventional radar but is still subject to the same
limitations. ARPA data is only as accurate as the data that
comes from inputs such as the gyro and speed log.

Types of ARPA
 In the early days, ARPAs of broad categories existed
and were generally referred to as “stand alone”
and “integral”
a)Stand-alone ARPA
These were primarily intended as additions to
conventional radars. They provided all of the ARPA
facilities but derived their data from “host” radar. This
was an attractive means of upgrading the ship’s
radar system without incurring the expense of
removing the existing radar and installing a new
ARPA system.

a) Stand-alone ARPA
Stand-alone equipment had to be interfaced to a variety of
existing equipment and while it was the less expensive
and more expedient of the two alternative, it was never
the solution and so, today, most of the ARPA’s being
fitted into the “integral” category.
Stand-alone ARPA works in two ways; The radar system
receives all the raw data and transmits all these data to
ARPA for processing. This may work, but having these
two units doing the work of a single one convinced the
ship owners that the dawn of new age in the electronic
navigation has come and they must be able to adopt to
the new system provided by this advancement in
science.

b) Integral ARPA
In the modern integral ARPAs, a computer, usually referred
to as the processor, is incorporated in the radar/ARPA
system so that the ARPA data can be displayed on the
same screen as the conventional radar data.
The main operational advantage is that the radar and ARPA
data are readily comparable. In practical terms, it is
much better than the same manufacturer is responsible
for the design, testing, installation and functioning of the
system.
Gradually the trend has been for all ARPA development to
follow this form, although there is still a small group who
continue to develop stand-alone modules.

How ARPA is used?
The ARPA is connected to the radar from which it automatically
extracts data, processes it and displays it along with graphics
and possibly alphanumeric. A computer forms the heart of
the system which plots the targets and displays the vector
associated with each tracked target.
Having first set up the ARPA display (as normal radar display),
select:
a) Range scale- e.g 12 miles
b) Plot- Relative (true) bearings
c) Mode- North-up (head-up or course up)
d) Mark the targets to be tracked (using joystick and gate)
e) Set the “vector length”--- in minutes
f) Check the course and speed input

General Features
• Daylight-bright high-resolution display
• 28 inch diagonal CRT presents radar picture of 360 mm
effective diameter with alphanumeric data area around it
• User friendly operation by combination of tactile backlit
touch pads, a trackball and rotary controls
• Audio-visual alert for targets in guard zone
• Echo trail to assess targets’ speed and course by
simulated afterglow
• Electronic plotting of up to 10 targets in different symbols
(This function is disabled when ARPA is activated)

General Features
• Electronic parallel index lines
• Interswitch (optional) built in radar or ARPA display unit
• Enhanced visual target detection by Echo Average, Echo
Stretch,
• Interference Rejector, and multi-level quantization
• Stylish display
• Choice of 10, 25 or 50 KW output for X-band; 30 KW
output for S-band,either in the transceiver aloft (gearbox)
or RF down (transceiver in bridge)
• Exclusive FURUNO MIC low noise receiver

ARPA Features
• Acquires up to 20 targets automatically
• Movement of tracked targets shown by true or relative vectors
(Vector length 1 to 99 min. selected in 1 min steps)
• Setting of nav lines, buoy marks and other symbols to enhance
navigation safety
• On-screen digital readouts of range, bearing, course, speed,
CPA, TCPA,
• BCR (Bow Crossing Range) and BCT (Bow Crossing Time) of
two targets out of all tracked targets.
• Audible and visual alarms against threatening targets coming
into operator-selected CPA/TCPA limits, lost targets, two guard
rings, visual alarm against system failure and target full situation

ARPA Features
• Electronic plotting of up to 10 targets in different symbols (This
function is disabled when ARPA is activated)
• Electronic parallel index lines
• Interswitching (optional) built in radar or ARPA display unit
• Enhanced visual target detection by Echo Average, Echo
Stretch,
• Interference Rejector, and multi-level quantization
• Stylish display
• Choice of 10,25 or 50 kW output for X-band; 30kw output for S-
band, either in the transceiver aloft (gearbox) or RF down
(transceiver in bridge)
• Exclusive FURUNO MIC low noise receiver
•

DISPLAY CONTROLS - MODE PANEL

 HM OFF- Temporarily erases the heading marker.
 ECHO TRAILS- Shows trails of target echoes in the form
of simulated afterglow.
 MODE- Selects presentation modes: Head-up, Head-
up/TB, North-up, Course-up, and True Motion.
 GUARD ALARM- Used for setting the guard alarm.
 EBL OFFSET- Activates and deactivates off-centering of
the sweep origin.
 BKGR COLOR- Selects the background color.
 INDEX LINES- Alternately shows and erases parallel index
lines.

 X2 ZOOM- enlarges a user selected portion of picture
twice as large as normal. (R-type only)
 CU, TM RESET- Resets the heading line to 000 in course-
up mode; moves own ship position 50% radius in stern
direction in the true motion mode.
 INT REJECT- Reduces mutual radar interference
 RANGE RINGS- Adjusts the brightness of range rings.

How is numerical data relating to a particular target
found?
By using the joystick and placing the gate marker ring over
a particular target, data in numerical form relating to that
target can be obtained:
a)range and bearing
b)course and speed
c)CPA and TCPA
This data may be made to appear sequentially
simultaneously on a special data display. Alternatively, alpha-
numeric may be used to make the data appear on the
display, alongside the particular target.

What extra facilities are available in the ARPA system?
1.Trial Maneuver
It should be possible to simulate the effect to a maneuver-- “own
ship”- o- on all tracked targets. This is done by the feeding in:
a)the propose course
b)the proposed speed
c)the delay(if any)
This display can be made to indicate the effect of such a
maneuver. The method is the display may be either static or
dynamic, in which case the tracked targets and own ship are made
to move at some 30 times normal speed. “Own Ship” will of course
move at the “propose” speed in the “proposed” direction with own
ship’s handling characteristics being taken into account.

2.Operational Warning
a)CPA warnings- it is possible to set limit of CPA and TCPA
which if violated by a tracked target, whether its vector
actually reaches the warning area or not, will activate an
alarm. The offending target will be by a brighter than normal
or flashing vector or a special symbol.
b)Guard rings and zones- it should also be possible to warn
the observer if any distinguishable target closes to a range or
transits a zone chosen by the observer. The first appear will
not activate the alarm. The existence of guard rings should
not be regarded as an alternative to keeping a proper
lookout.

2.Operational Warning
c)Target lost- the ARPA should clearly indicate if a target is
lost with the last tracked position being clearly indicated.
Methods of Displaying Information
Since the first computerized radar system came on the
market and to this very day many different ways of
presenting the information has been developed, produced
and delivered. Today, regardless of graphic presentation, all
ARPA systems must be able to present target information in
form of both relative and true vectors.

Methods of Displaying Information
 Both time of vectors should be time adjustable. In addition
to displaying target information graphically, all ARPA’s also
display target information digitally on the traffic display or on
a separate screen.
 In additional a number of graphical symbols are used for
different purposes:
Defining stationary targets
Indicating navigational marks
Sailing routes
Pointing out targets that cause alarms etc.

ARPA’s Graphical Symbols
Symbols and Definition
 TV - True Speed Vector indicates the targets speed and
course.

 RV - Relative Speed Vector indicates target relative
course and speed.

 TH - Track History should be provided on request,
consisting of at least four equally spaced past positions of the
echo.

 PPC - POINT OF POSSIBLE COLLISION is the point at
which a collision could take place.

 PAD - Predicted Area Of Danger is the area to be
avoided based on CPA and TCPA setting and relative target
speed.

Area Rejection Boundaries (ARBs, AEBs)
 It is possible to place electronic lines on the
screen which eliminate automatic plotting in
selected areas. The lines are adjusted for “rotation”
and “transaction” controls. These reduced the load
on the tracker when in the proximity to a coast echo.
Alternative systems provide automatic acquisition
in zones which may be designated by range and
sector controls.

Equipment Fault in ARPA system
a.Connection with other equipment
The connection of the ARPA to any other equipment should
not downgrade the performance of that equipment. The
failure of an input from other equipment, such as log or
compass, should activate an alarm.
b.Performance tests and warnings
Self diagnosis should activate a warning in the event of ARPA
malfunction. Also means shall be available to check the
correct interpretation of data against a known solution.

What alternatives facilities are available on
ARPA system?
a.Automatic Acquisition
It is permissible for targets to automatically, as well as
manually acquired. But where automatic acquisition is
provided, the operator must be able to select the areas in
which it operates.
b.Manual Acquisition
The operator specifies the target to be subsequently tracked.
To do this, a joystick and screen marker or tracker ball and
screen marker are used. The target is entered into or
removed from the computer memory when the acquire or
cancel button is press.

What alternatives facilities are available on ARPA system?
c.Tracking and Acquisition Limits
There will may be times when targets are close to own ship but
present no real threat, and whose vectors may well clutter up the
center of the display. It may be possible therefore to set limits on
the ranges at which targets are acquired and to which they are
tracked.
d.Potential Points of Collision (PPCs)
From the basic plot of a target, it is possible to determine the
course to steer in order a collision or interception will take place.
It is possible to have these PPCs appear on the display and in
this way, allow the navigator to avoid them.

e.Predicted Areas of Danger (PAD)
It is logical step from PPCs to indicate areas around these points
into which vessel should not do in order to ensure that some
specified clearing range is maintained.
These predicted areas of danger are feature of the Sperry
Collision Avoidance System. Earlier models as appear as
ellipse is not necessarily the PPC.
f.Methods of Testing an ARPA for malfunction
These usually take the form of self-diagnostic routines with
some indicator of the unit or Printed Circuit Board which is found
to be faulty.

g.ARPA facilities
Finally the first true ARPA appeared, a system able to extract the
signal from the targets then pass them to a digital processor.
Once the data is within the processor of these equipment, a
variety of facilities will present information to the observer.
These facilities includes:
1.Relative Vectors 6. Trial Maneuver
2.True Vectors Output 7. Digital Data
3.Points of Collision 8. Navigational Lines and Limits
4.Predicted Areas of Warning9. Operational Danger
5.History of Warning 10. Equipment
11. Rejection Boundaries

• This section gives you information about IMO requirements
for ARPA system including performance standard for gyro
and log.
Performance Standards for Automatic Rad

 At the end of the grading period, the students will be able
to demonstrates a knowledge and understanding of the
following:
• Theory of ARPA Tracking System
• Tracking Window
• Setting Up Maintaining Displays
• Risk of Over -Reliance on ARPA

Theory of ARPA Tracking System
 Explains processing delay and other important
limitations in the system. When operating the
ARPA in Automatic Acquisition mode, the
operator must be aware of the following tracking
system limitations:
a.Normally the sensitivity of the ARPA tracking
system is reduced when operating in Automatic
acquisition mode.

b. When the “guard ring” philosophy is used by the
ARPA tracking system, echoes can escape
acquisition because the radar at a range closer that
the distance to the inner guard ring detects them or
the echoes remain between guard rings.

c. When the “search area” philosophy is used,
echoes can escape acquisition because they
are outside the specified area or to many
echoes are picked up, resulting in system
overload.

Tracking Window
 The number of sweeps being digitized in each
tracking gate depends on the tracking
philosophy used by the actual ARPA
manufacturer. Several sweeps will always be
required.
 In order to start digitizing the analogue radar
echo is not lost by too many scans during a
specified time, as this will result in rejection of
defining the echo as a possible target and no
further processing will be executed.

Tracking Window
 To define the echo as a target of interest, a minimum
number of sweeps inside the gate must be defined
above the threshold. A good working and properly
turned ARPA tracking system should be capable of
acquiring all echoes, which can be seen by the human
eye.
 Each of the radar echoes we want to plot must be
processed like this. The different ARPA manufacturers
us different position on digitized echo as reference for
further processing. Possible target reference points are:
 The front edge
 The center
 Or the back of the digitized radar echo

Tracking Window
0 0 0 0 0
0 1 1 1 0
0 1 1 1 0
0 1 1 1 0
0 0 0 0 0
Sweep 1 2 3 4 5
 Each reference point has its advantages or
disadvantages. In our example we use the center of the
target as reference.

Setting Up Maintaining Displays
Kinds of Warnings
 Collision Warning -- audible and flashing warning
activated whenever a traced target violates the pre-
set collision criteria.
 Lost Target -- audible and flashing warning
activated whenever the system no longer can track
a target.
 System Alarm -- audible and flashing warning
activated when a pre-set limit is violated.

 The ARPA system Start Up procedure varies from
system to system however, the following points
outline the minimum of what must be checked
before an ARPA is operated in basic mode.
 Overlooking one or more of these points may cause
serious consequences:
1. Switch on the ARPA and checked that required
radar is connected and properly adjust.
2. Check that the ships connected course is feed into
system.
3. Check that the radar antenna alignment is correct,
if not, correct it.

 Overlooking one or more of these points may cause
serious consequences:
4. Check that required log is selected
5. Select required radar mode, normally True Motion,
Course Up or True Motion, North Up should be use
for traffic surveillance purposes
6. Select required range, vector length and collision
warning criteria
7. Familiarize yourself with the ARPA manufacturers
recommended start up procedures and other
recommendations.

 If navigation features are available on your ARPA
and you intend to use them, the following
additional points must be checked:
a. Date and time should be displayed correctly on the
ARPA information screen.
b. Own ships position input must be kept correct on
the ARPA at all times, otherwise all position must be
calculated by the ARPA will be incorrect.
c. In coastal areas, navigation check-points should be
marked on the ARPA in order to assist the navigator
in detecting the possible positioning error as soon
as possible.

 If navigation features are available on your ARPA
and you intend to use them, the following
additional points must be checked:
d. Special requirements pointed out by the ARPA
manufacturer
 The main purpose of the ARPA is to provide the
navigator with the possible overview of the traffic
situation at all times.

The Importance of Incorrect Speed Input
Ship B
Course/Speed
Ship C
Course/Speed
Ship D
Course/Speed
Result
Correct
El. log
1 040-2,0 210-7,0 270-5,0 Calculation
Aspect
2 032-2,4 212-6,4 272-5,0 Small
Errors
Manual
3 119-1,22 204-8,7 248-5,6 Dangerous
Errors
Doppler
4 220-0,5 213-9,5 253-7,2 Dangerous
Errors
Doppler

The Importance of Incorrect Speed Input
 The table presents ARPA calculated result as given
by four different speed input sources:
1. Electromagnetic log which gives correct speed
through water.
2. Manual speed input, miscalculated by +0.5 knots
3. Doppler log provides speed over ground without
compensating for transverse drift.
4. Doppler log provides speed over ground and
compensates for transverse drift.

Risk of Over Reliance on ARPA
Problems may occur in using ARPA
1. The risks of over-reliance on ARPA
 Appreciation that ARPA is only navigational aid and
that’s its limitations, including those of its sensors,
make over-reliance on the ARPA dangerous in
particular for keeping a look-out, the heed to
comply at all times with the basic principles and
operational guidance for officers in-charged of a
navigational watch.

1. The risks of over-reliance on ARPA
Risk:
 impressive system
 no system is better that the weakest part
 the operator must be aware of the ARPA limitations
 An ARPA system in the hand of unqualified
personnel is not only dangerous, but can indirectly
be the main reason for an accident.

2. Errors and Precautions
 Errors in an ARPA system can be divided into
groups:
a. errors in sensors (radar, log, gyro, etc.)
b. errors in ARPA software
c. errors in ARPA hardware
d. errors in interpretation of the actual display
 When working with computerized systems, always
remember “Rubbish-in-Rubbish-out” simple as
that.

3. Errors in Interpretation of Display
 Here are some possible treats:
a. raster scan ARPA display “lock up”
b. mixing trial and real time information
c. wrong speed input or overlooking type of speed
input to the ARPA
d. no correction for gyro course error before input to
ARPA
e. misinterpretation of display symbols may cause
severe problems

3. Errors in Interpretation of Display
f. operating long periods in “impure presentation” may
have serious consequences
g. exclusive reliance of ARPA will sooner or later give
you a problem
 Remember that ARPA is only a navigational aid and
that its limitations including those of its sensors,
make exclusive use of ARPA dangerous.

4. Automatic Acquisition Precaution
 The majority of ARPA systems manufactured today
provide and automatic acquisition feature. This feature
may reduce the operator’s workload during busy
periods and thus contributing possibility to safe sailing.
 However, the operator should be aware of the fact that
most ARPA systems are less sensitive in auto-
acquisition mode than in manual acquisition mode. This
is one good reason not to rely on the new target
warning only, but at regular intervals visually observe
the ARPA screen to make sure that all targets are
acquired.

5. Factors affecting system performance and
accuracy:
a. Knowledge of ARPA sensor input performance-
radar, compass and speed inputs, effects of sensor
malfunction on the accuracy of ARPA data.
b. Effects of the limitations of radar range and bearing
discrimination and accuracy, the limitations of
compass and speed input accuracy on the
accuracy of ARPA data.
c. Knowledge of factors which influence vector
accuracy.

6. Tracking capabilities and limitations
a. Knowledge of the criteria for the selection of targets
by automatic acquisition
b. Factors leading to the correct choice of targets for
manual acquisition
c. Effects on tracking of “lost” targets and target fading
d. Circumstances causing “target swoop” and its
effects on displayed data

7. Processing delay
 The delays inherent in the display of processed
ARPA information, particularly on acquisition and
re-acquisition or when target maneuvers.
8. When and how to use the operational warnings,
their benefits and limitations
 Appreciation of the uses, benefits and limitations of
ARPA operational warnings, correct setting, where
applicable, to avoid spurious interference.

9. System Operational test
a. Methods of testing for malfunctions of ARPA
systems, including functional self-testing
b. Precautions to be taken after a malfunction occur
10. Manual and automatic acquisition of targets
and their respective limitations
 Knowledge of the limits imposed on both types of
acquisition in multi-target scenarios, effects on
acquisition of target fading and target swoop.

11. When and how to use true and relative vectors
and typical; graphic representation of target
information and danger areas
a. Thorough knowledge of true and relative vectors,
derivation of targets true courses and speeds
b. Threat assessment; derivation of predicted closest
point of approach from forward extrapolation of
vectors, the use of graphic representation of danger
areas

11. When and how to use true and relative vectors
and typical; graphic representation of target
information and danger areas
c. Effects of alterations of courses and/or speeds of
own ship and/or targets on predicted closest point
of approach and predicted time to closest point of
approach and danger areas
d. Effects of incorrect vectors and danger areas
e. Benefit of switching between true and relative
vectors

12. When and how to use information on past
position of targets being tracked
 Knowledge of derivation of past positions of targets
being tracked, recognition of historic data as means
of indicating recent maneuvering of targets and as
a method of checking the validity of the ARPA’s
tracking.

13. Setting up and maintaining displays
 Selection of the time scale of vectors/graphics
a. Use of exclusion areas when automatic acquisition
is employed by ARPA
b. Performance checks of radar, compass, speed
input sensors and ARPA

14. System Operational Test
 System check and determining data accuracy of
ARPA including the trial maneuver facility by
checking against basic radar plot.

15. When and how to obtain information from ARPA
display
 Demonstrate ability to obtain information in both
relative and true motion modes of displays
including:
a. Identification of critical echoes
b. Used of exclusion areas in automatic acquisition
mode
c. Speed and direction of targets relative movement

display
including:
d. Time and predicted range at targets closest point of
approach
e. Course and speed of the targets
f. Detecting course and speed changes of targets and
Limitations of such information

display
including:
g. Effect of changes in own ship’s course or speed or
both
h. Operation of the trial maneuver

Operational Use of Radar Guide

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