Radar Flashcards
Navigational equipment Required for a vessel 2999GT?
Magnetic Compass
Gyro Compass
Means of taking a bearing
Echo sounder
GPS
LOG
Rudder angle indicator
Radar, both 3 and 9 (what?)
ECDIS
AIS
Signaling lamp
Met Instruments
Search light
EPIRB
SART
BNWAS
LRIT
What is X band and S Band
X band 3cm 9GHz
Shorter pulse, better definition, better for navigation, taking bearings etc
Detects SARTs!
S band 10cm 9GHz
Longer pulse, more energy, better for detecting targets and collision avoidance
Better in Rain
Physically larger scanner
Short Pulse vs Long pulse
Short pulse, higher frequency of pulses
Better definition of return
Lower energy may mean small/distant targets do not get picked up
Long pulse, lower frequency of pulses
Worse definition, blobbier image
Better chance of picking up weak targets
How does sea clutter work
A/C Sea, (STC) Sea control, also called Sensitivity Time Constant
suppresses reflections from waves near own ship. It reduces the sensitivity of the receiver from the centre out.
The proper setting should be such that the clutter is suppressed, and echoes become distinguishable.
If the control is set too high, both sea clutter and true echoes will disappear from the display
How does Rain Clutter Work
Called Precipitation clutter A/C Rain
The rain control suppresses the reflected echoes from rain, hail and snow to clear the display.
Via video processing it does not display the leading-edge returns.
On the X-band radar, because of its short pulse length, the echoes from legitimate
contacts can become lost in the echoes from precipitation, called rain clutter. When rain clutter masks the display, adjust this control to break up the clutter and distinguish echoes.
Adjust the control so that the clutter just disappears; too much A/C rain action may shrink or erase the echoes from legitimate targets.
Difference between shadow and blind sectors
both caused by obstructions on the radar’s horizon
Could be masts, antennas or land masses
Shadow is partially obstructed, causing reduced sensitivity in that area
Blind is fully obscured, no targets will be detected in this area, only multipath echoes (False Echoes)
What characteristics effects the detection of radar targets
MAST
Material - Metal is best
Aspect - The angle can reflect the radar pulse up/down instead of back to scanner
Size - Larger is better, particularly the height of the object
Texture - Very smooth/flat will be harder to detect
This also applies to land/coast. Cliffs good, low lying sand/beaches will be inconsistant
Types of Radar error/limitation
Side lobe effect - spiil from scanner causing smear
Spurious echoes
Radar interference
Indirect echoes - caused by obstructions
Multiple echoes - 2nd/3rd bounce
Shadow and Blind sectors
Radar horizon - dependant on height of scanner to bow
Checking that any video preocessing effects are applied corrrectly or removed to get the true picture
Setting up radar for use
Check for obstructions, workers aloft, permit to work
Brilliance - Adjust for day/night, turn up until the time-base trace is just visable
Range - Suitable for area/traffic
Gain- start at 0, turn up until light speckling appears, then down until its just gone
Tuning - tune for best display. works best with a target, if not, sea clutter, or even your own wake,
Clutter - start from 0, bring up for best display
Re-adjust after 10 mins, when the kit has warmed up
Then every hour, to match the changing conditions
What would you check on the radar before departure
‘Performance monitor’ function, before sailing and every 4 hrs
VRM checked against range rings
EBL checked against ships compass of a conspicuous object
Check Ships head marker by comparing true ships head vs reported ships head on the Radar display
Check the displayed ships head marker is aligned with the For-aft line of the ship, by comparing the True compass bearing of a small distant target, vs the relative bearing on the display
What is the built in radar test called, what is it?
The performance monitor function
Should be done before sailing and then every 4 hours
Produces a plume on the display, showing the power of the magnetron
If the plume is shrinking, the magnetron is losing power
Modern radars do a self test
Magnetrons need replacing every 10,000 hours
Good radar practise/ limitations of radar
Good Radar Practice/Limitations of Radar
* The quality of the performance of the radar needs to be checked regularly: A performance monitor if fitted should be used for this purpose.
* Misalignment of the heading marker, even if only slightly, can lead to dangerously misleading interpretation of potential collision situations.
* Small vessels, ice and other floating objects such as containers may not be detected by the radar.
* Video processing techniques should be used with care.
* Echoes may be obscured by sea or rain clutter.
* Masts or other structural features may cause shadow or blind sectors on the display.
When to use Sea stabilised/ground stabilised
What stabilises it?
Ground/SOG for pilotage/navigation, better fore seeing movement in relation to land/bouys etc, to see the effect of tide
Sea/STW for collision avoidance, gives true representation of aspect, tide is ignored/effects both equally
Can be by doppler log or GPS
Head up, North up, course up differences
Head up, default setting, reverts to this if loses gyro input
matches up to the view out the window
unstabilised, as ship yaws, targets will appear to move as well, difficult to determine risk of collision
North up, Gyro stabilised
Better represents the chart
Course up, gyro stabilised
Better represents the view out the window
True motion vs relative motion
True motion, you will move accross the screen, land will appear fixed
Requires accurate speed and heading info of your own vessel to give accurate speed and heading of another
Relative motion, you will be stationary, in center or offset, land will pass you
How to set radar to detect SART
X-Band radar!
6-12 Mile range
Detune the radar - reduces the clutter without reducing the SART response
leave gain as normal
Sea clutter should be set to a minimum
Rain control as normal for the conditions
Rule 19 A,B,D,E
A)This rule applies to vessels not in sight of one another in or near a area of restricted visability
B)Every vessel shall proceed at a safe speed adapted to the conditions. Engines shall be ready for immediate manoeuver
Di) When altering course, we should avoid turning to port for a vessel forward of the beam, unless overtaking
Dii) Should avoid turning towards a vessel abeam or abaft the beam.
E) Every vessel that detects another vessel forward of the beam, shall reduce speed to a minimum, and if necessary, take all way off
Rule 8 E?`
If necessary to avoid collision, or to allow more time to assess the situation, a vessel shall slacken her speed or take all way off by reversing her means of propulsion.
Process for radar plotting
Put on own heading
Set range scale and plot length to use
Plot 3 points to get OA,
When continued this is the relative motion line (>)
And allows CPA to be measured
TCPA = distance from (A-CPA / OA) X Plot length
If CPA is unacceptable:
Mark WO on own heading line, Parallel to targets O
Complete triangle to get WA, parallel to get heading
Difference between their heading and bearing to them gives aspect
When are manoeuvrering signals used? what are they supplemented by?
When vessels are in sight of one another
Supplemented by light signals
Where can we get more guidance on restricted vis
MGN 369 Navigation in Resticted Visability
What does (M+F) mean on an MGN
Merchant and Fishing
Some key points from MGN 369
Navigating in restricted vis requires a full undersatnding of part B III Rule 19 as well as Part B I Rules 4-10
It is the responsibility of the OOW to comply with the colregs
Rule 19 is the basis for nav in reduced visability, requireing all vessels to proceed at a safe speed as per rule 6
There is no stand on vessel in restricted Vis, all participants are required to take appropriate action
Use all available means to apraise the situation and evaluate the information before taking action
Actions on encountering Fog
Call master
Fog signal
Close watertight doors
Re-assess safe speed, slow down
Have engines ready for immediate manouevre
Post additional lookouts - sight and sound
Nav lights on
Where can we get more guidance on Arpa and electronic navigation aids
MGN 379 Use of Electronic Navigation Aids
What is Arpa and what should it be capable of according to MGN 379
Automatic Radar Plotting Aid
For ships over 10,000 GT
Manual or automatic acquisition of targets
Automatic tracking and display of all relevant target info for a t least 20 targets
Have a trial manoeuvre function
What is ATA and what should it be capable of according to MGN …
MGN 379
Automatic Tracking Aid
Ships 500GT and over
Manual Acquisition over targets
Automatic tracking and display of at least 10 targets
What will happen if you are sea stabilised in a coastal area
If there is a strong current or leeway experienced,
All land masses will produce trails, potentially created a cluttered screen
MGN 379 - To estimate risk of collision….
To estimate risk of collision with another vessel, the Closest point of Approach (CPA) must be established, Choice of appropriate action is made by knowledge of the other vessels track using manual or automatic plotting methods
MGN 379 - The accuracy of the plot, however optained, depends on …
The accuracy of the plot, however obtained,depends upon accurate measurement of own ship’s track during the plotting interval.
Innacurate compass heading or speed input will reduce the accuracy of true vectors when using ARPA or ATA
This is particularly important on reciprocal courses as could lead to a dangerous misinterpretation of the other vessels true track,
The apparent precision of digital read outs should be treated with caution
MGN 379 - If 2 radars are fitted, it is good practise to…
Use one for collision avoidance and one for navigation
Is manual plotting equipment still accepted?
No, (except for existing vessels still compying with Solas V 74)
Does Sea or ground stabilisation affect the CPA
No, relative motion of the target is unaffected by the choice of stabilisation
Are true or realtive vectors better for collision avoidance
Relative
Slight inacuracies in inputs could give inacurate outputs of true vectors
