N&R Questions Flashcards
What information should ARPA give within 3 minutes?
Full Report Time Bearing Range Target course Target speed CPA TCPA
What is meant by Geometric Dilution of precision?
Relates to orientation of the satellites around the receiver. If they give a shallow angle of cut between the position lines accuracy is downgraded.
How long should it take ARPA to give the user a relative vector on a acquired target?
1 Minute
What is CATZOC’S A1, A2 and B
Draw symbol
Sea floor coverage - for both A1 A2
Full area search undertaken
Significant seafloor features detected and depth measured
A1 position accuracy +/- 5m+5% (6 stars)
A2 position accuracy +/- 20m (5 stars)
B position accuracy +/- 50m (4 stars)
Why is horizontal datum important when plotting a GPS position on a chart?
A specific point can have different coordinates depending on the datum used.
List 5 items that could possibly be listed on a chart
Tidal Diamond Tables Notes Warnings Tables of tidal levels Crown copyright statement
Explain Parallel index lines?
Uses?
A PI is an adjustable electronic line on the radar display, set parallel to the ships track and at a set distance off.
Using a PI for coastal navigation is te safest and easiet method of keeping a ship on track
Great care should be taken in identifying and confirming reference points on the chart and on the radar and in verifying the radar range when using the parallel index.
List three different chart projections
Gnomonic
Transverse Mercator
Mercator
(Radar)
How can you confirm an echo is an indirect echo?
Turn gain all the way up and the radar will show the blind spot and this is where the indirect echo/target will be.
What two logs can measure speed of the ground ?
Doppler
Acoustic
What does MKD stand for and what are its disadvantages over a fully integrated AIS system
Minimum keyboard device
Extraction of details is tedious and prone to keying errors
3 Things that can be done to help minimize the effects of deviation on a binnicle
Three correctors used to minimise deviation are flinders bars and kelvins spheres for soft iron (induced magnetism) and vertical correctors for hard iron (permanent magnetism)
What information is within the annual summary of notices to mariners?
NP247
A database with details of history of corrections for all charts and sailing directions by the British admiralty or UKHO
Primary occasions and reasons for range adjustment within echo/depth sounder?
Give kHz values?
Different ocean depths
50khz wider pulse deeper waters but wont give as clear of as a picture
200khz narrower pulse shallow waters better detail, works better with aeration. Waters less than 100m
What effect will the sun’s radiation have on the Ionosphere? How will it effect the distance radio waves can travel?
It thickens the Ionosphere.
Radio reception distances are negatively affected during day time.
Better reception distances after sunset.
Effect on values shown by depth sounder in fresh water opposed to salt water and why?
Fresh water will indicate up to 3% more than the actual depth.
Acoustic signal travels faster in more dense water.
Main factors which might affect Radar target detection (5)
MASTS
Material- composition of the target
Aspect- Flat plate 90 degrees will give a good return, other angles can reflect energy away
Size- Greater the size, better return
Texture -flat better than rough
Shape - square is better than spherical
Define bearing discrimination
Refers to the ability of the set to show separately two similar targets at the SAME RANGE but SLIGHTLY DIFFERENT BEARINGS
Main components of Radar
Trasmitter
Scanner
Receiver
Display
ECDIS - Full display
Contains all the encoded chart objects
As the base display this is also not recommended for navigation as it clutters the display
What projections would you use for a great circle route
Gnomonic projection
Function of Gain Control on a depth sounder
Controls the sensitivity of the device and works on the amplifier, too much gain with a rocky seabed and multiple echoes are received.
5 ECDIS warnings or indications ?
Route planning across specified area Route planning across safety contour Information over scale Larger scale ENC available Positioning system failure Position test failure
Radar acronym for?
Radio detection and ranging
RAdioDectionAndRanging
What sections are in the weekly notice to mariners ?
- Explanatory notes. Publications list
- Admiralty notice to mariners. Updates to standard charts
- Reprints of NAV AREA 1 - navigational warning
- Updates to ADMIRALTY sailing directions
- Updates to ADMIRALTY lists of lights and fog signals
- Updates to ADMIRALTY List of radio signals
- Updates to miscellaneous ADMIRALTY nautical publications
- Updates to ADMIRALTY digital products and services
Explain Precession with regards to Gyro, how is it helpful to establish True North?
A gyroscope possesses the property of precision meaning if a force is applied to one end of the axle it will move at 90 degrees to it.
A gyroscope becomes a Gyrocompass by modifying it to become a north seeking instrument.
How fast does sound travel in water?
1500 m/sec
Priciple differences between ARPA and ATA(Auto Tracking Aid)
Acquistion
ATA - manual
ARPA - manual and optionally automatic
Minimum tracked target capability
ATA - 20
ARPA- 40
History dots
ATA- None required
ARPA- 4 equally spaced
Trail Manoeuvre
ATA- None
ARPA- Yes
What is the average length of radio antenna?
One quarter of a wave length
Principle of GPS
A global positioning system used for the purpose of navigation and detection of objects and places which is based on the ‘trilateration’ mathematical principle.
3 Satellites giving 3 position lines are required for a 3D fix.
4th satellite is required for time.
Usually on board GPS receiver is fixing from 6 or more satellites.
ECDIS - Standard display?
Used for normal navigation
A requirement that it can be selected AT ANY TIME WITH A SINGLE OPERATOR ACTION.
As well as the base layer contains-
Drying lines Buoys Other navigation marks Prohibited, Precautionary and restricted areas Separation and traffic routing
What projection would you for use for a great circle route ?
Gnomonic projection
How are ENCs updated and corrected?
Updates are issued weekly in electronic format and available via internet.
What does the trial fuction allow the operator to do? (ARPA)
Trial a manoeuvre and the effect on all tracked targets
What publication can you find the meanings of chart symbols found on British admiralty charts?
NP….?
NP5011
Symbols and abbreviations used on admiralty paper charts
At the change of watch with regard to AIS what needs to be checked?
That the manual information that is imputed correct
Define range discrimination
Refers to the ability of the set to show separately two similar targets on the SAME BEARING but on SLIGHTLY DIFFERENT RANGES
What are T’s and P’s and what is the procedure for marking them on a chart?
Temporary and Preliminary Notices.
Should be marked in pencil only together with the notice number and date.
Principle of a echo sounder
Transmission of a pulse of energy or signal
Which measures the time difference between transmission and return of energy/signal.
Time distance velocity calculation will give you the depth.
Explain the origin of the Janus Configuration
Roman god who was able to see in the past and future
List 5 publications important to take on a passage
Sailing directions Ocean passages of the world Chart catalog Tide tables List of lights and fog signals
What is contained in section 2 of the annual summary of notice to mariners ?
Section 2:
Temporary and preliminary notices
5 different logs
Towed Impeller Electromagnetic Doppler Pressure Acoustic
Five ECDIS mandatory alarms
Crossing safety alarm Deviation from route Position system failure Approach to critic point Different geodetic datum
What are Pseudo ranges?
The distance between a satellite and navigation satellite receiver .
How fast does an electromagnetic wave travel?
Speed of light
300 000 000 meters per second
What is the principle of the electromagnetic log?
What can cause errors?
Advantages and disadvantages
Fin shaped sensor protruded from hull
Which incorporates a coil and two electrodes
When the ship begins to move the speed of the water (being a conductor in a magnetic field) increases, thereby causing an increase in the voltage between the two electrodes..
Accuracy within 0.15 kts
Can be measured when going astern
ERRORS:
Variations in temperature
Turbulent motion
Advantages
Simple operation
Works ahead and astern
Accurate at low speeds
Disadvantages
STW only
Externally mounted
Function of Tune and Gain on a Radar
Tune adjusts the frequency generated in the receiver which will be mixed with the returning signals.
Gain controls the degree of amplification of the incoming signal.
Where is the best position for a gyro
Lowest possible
Centre line
Amidships if possible
List 5 mandatory alarms & 5 indications or warnings
Write them down!
MANDATORY ALARMS Crossing safety contour Deviation from route Positioning system failure Approach to critical point Different geodetic datum
INDICATIONS OR WARNINGS Information over scale Larger scale ENC available Different reference system Route planning access safety contour Route planning across specified area Positioning system failure Position Test failure
How often should you check the ships deviation
Change of watch
After ship has sat for long periods in one place
After shipyard - (structural changes, additions or alterations to vessel)
Describe ECDIS Base display?
List information that is found on this display
The absolute minimum information considered necessary for navigation such as -
Coast line Fixed structures Overhead wires Safety contour Scale, range and north arrow
NOT RECOMMENDED FOR NAVIGATION
However can be used when de-cluttering the screen to check ahead on a small scale
List 5 errors that may occur within the gps system
Mulitpath error Satellite clock Orbital or ephemeris HDOP Horizontal Dilution of precision Horizontal datum Ionosphere Tropospheric
What is the difference between a map and a chart
A chart is a LIVING DOCUMENT and is continuously updated.
A map is not continuously updated (until theres a new addition printed)
Draw and label a binnicle
Draw
Why does a pressure log not work effectively in shallow water?
Because it protrudes beneath the hull it’s use is limited in very shallow water
What considerations should be taken in to account when using a Doppler log with a true motion, ground stabilized radar display?
The Doppler system normally measures speed over the ground to a depth of about 200m after this depth the signals may be returned of a deep colder layer of water called the DSL deep scattering layer.
Most units will automatically switch from ground speed to water speed at about 200m
Difference between ECDIS and RCDS
ECDIS is a complete integrated navigation system, displays ENCs made up of multiple layers of information that can be interrogated.
RCDS displays raster charts and can be interfaced with GPS to show the vessel’s position.
How does a GPS receiver determine an exact fix from pseudo ranges?
Ranges from 3 satellites will result in a “cocked hat”. Because the error is the same for each reading it can be determined and an accurate position can be computed.
Interference of echo sounders
Mechanical noise Electrical noise Water noise Aeration Temperature
Advantages and disadvantages of a gyro compass?
Advantages
Unaffected by magnetism
Suffers neither variation nor deviation error
Disadvantages
Reliant on power
Cumulative errors when subjected to prolonged high speed maneuvers
May take several hours to resettle after power failure
Explain what is meant by CATZOC’S
Category zones of confidential
Category Zone of Confidence (CATZOC) values are assigned to geographical areas to indicate whether data meets a minimum set of criteria for position, depth accuracy and seafloor coverage. The Zone of Confidence (ZOC) value is dependent on the positional and depth accuracy of the survey.
How many reporter can the AIS system handle per minute?
4500
What is meant by- and give there values
VBW
HBW
Vertical beam width 25-30degrees
Horizontal beam width 1degrees
Explain with a diagram E/LORAN C basic principle?
Position fixing system based on measuring the time difference between master and slave pulses making up a loran chain.
Made up of
1 master 4 slaves
What is the principle of the Doppler log?
What is the JANUS CONFIGURATION ?
What can cause errors?
Utilizes a transducer fitted flush with the hull. This will reduce drag and possible fouling.
Optimal angle 60 degree.
Emits acoustic energy at 1500m/s
The Log uses the Doppler effect which is observed when there is a shift in frequency between a transmitted signal and a received signal caused by the movement of the sound source.
JANUS CONFIGURATION
Is the addition of from 2-4 transducer at the same angle but facing at the opposite angles at 60 degrees
Overcomes the error from any vertical motion of the ship from sea and Pythagoras error
ERRORS Vibrations Temperature Density Salinity
Draw sun earth moon diagram for SPRING TIDES
Draw sun earth moon diagram for NEAP TIDES
Draw tide levels diagram and charted data
Range by vertical angle equation
Height of object divided by angle in minutes x 1.852 (1.856)
Draw and describe components of radar
Antenna/Scanner
Radiates pulse at 360 degrees
Motor
Wave guides (hollow copper tubing, connects transmitter/receiver to duplexer and the to motor)
T/R cell (duplexer) opening and closing between transmitting and receiving (v fast)
Transmitter < Split to > receiver which has an amplifier (because returning signals are weaker
Power source
Display
Draw and label a wave terminology diagram
Wavelength is the distance between the crests of two successive waves, one wave being known as a cycle. Amplitude is the height of the wave and frequency is the number of cycles or waves passing a fixed point in one second. One cycle per second is one Hertz.
Describe with the aid of a sketch the cause of Multiple Echoes and the effect on the radar display (4)
A radar pulse bounces off a target at close range, with enough power in it to allow
it to bounce back and forth several times, painting an echo each time received.
Describe with the aid of diagrams the cause of Indirect Echoes and the effect on the radar display (4)
The radar pulse bounces off some obstruction on the ship before hitting a target, with the echo being received by the same route. The radar thinks the target is in the direction of the obstruction, but at the distance of the target.
Describe with the aid of diagrams the cause of Side Lobes and the effect on the radar display (4)
Side lobes are escape of electromagnetic radiation near to the scanner, if they pick up targets in this area, extra echoes will be painted in the direction of the lobes.
Describe with the aid of DIAGRAMS the cause of Blind and Shadow Sectors and the effect on the radar display
Blind sectors are areas where the radar transmissions are completely obscured and no echoes will be found. Shadow sectors are areas of reduced sensitivity where radar may pick up some targets.
Draw and describe second trace errors (Radar)
ARPA Target ID order
BRG RANGE COURSE SPEED CPA TCPA BCR BOW CROSSING RANGE BCR BOW CROSSING RANGE
Draw the system components of a echo sounder diagram
With the aid of a diagram, describe and explain the echo sounding principle.
Four main parts.
CPU - generates electrical pulses and starts the clock
Transducer - transmits a sound pulse which is return from sea floor and then sent to back to the CPU to calculate the depth.
Time base
Display
With the aid of a diagram explain the difference between ground, sky and space waves
Ground Waves tend to follow the curvature of the earth
Ground waves are refracted downwards due to the atmosphere. At low frequencies the transmissions tend to be absorbed into the earth.
Those that reach to the horizon are Space waves
Those that travel upwards away from the surface of the earth are called Sky Waves. At medium frequencies they tend to follow the curvature of the earth and at higher frequencies (VHF and above) they travel virtually in straight lines and are then known as sky waves.
Describe the effects of radar interference and how an operator may account for this interference
Radar interference is when to radars on the same frequency create an interference on the displace
IR adjuster will change your frequency to stop this. You will need to adjust this back once you have past the interfering vessel.
