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
What does ARPA stand for?
Automatic Radar Plotting Aid
What does ECDIS stand for?
Electronic Chart Display and Information System
What does FTC and STC stand for and what do their functions do to the radar display
FTC- FAST TIME CONSTANT
Rain clutter
Rain can be visible on the screen and mask other targets.
This control reduces all echoes so that only their leading edges show, which can help detect targets ‘lost’ in rain clutter.
STC- SENSITIVITY TIME CONTROL
Sea clutter
is used to reduce the amount of sea clutter (echoes of waves) appearing on the screen.
These will be strongest near the CENTRE of the display. The control REDUCES the gain in the centre of the screen, and by a decreasing amount further out, both amounts depending on the setting.
List 8 publications published by the British admiralty
Sailing directions List of lights and fog signals NP86 List of radio signals NP281 part 1&2 Tide tables NP 202 Chart Catalog NP 131 Ocean passages of the world NP 136 Symbols and abbreviations NP5011 The mariners handbook NP100
What information is contained within satellite signal received by GPS receiver?
Emphemeris position
Time signal was sent
Position of other satellites
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
Explain what is meant by horizontal datum
Is a reference point determined by scientific bodies as being the centre of earth from which all position on earth are measured
2 advantages of raster charts?
2 disadvantages of vector?
Raster :
Looks familiar (same as paper chart)
Cheaper
Vector :
Can become cluttered
Removing layers and a the change of watch its not discussed
Over reliance
3 types of AIS
REAL AIS - signal comes from the actual buoy/ship
SYNTHETIC (Monitored/Predicted) monitored= position transmitted by shore - a physical object without a transmitter
VIRTUAL - example - not actually there. (Sunken ship below /EVERGREEN) data transmitted by shore.
System error, probability basis %?
Maximum error?
95% probability error
33meters error
Difference between Raster and Vector chart
Raster
is a direct digital reproduction of a paper chart produced by scanning. Text and symbols may become over magnified when zooming in.
Large file size, not seamless, distraction when zooming
Vector is a digital chart made up of multiple layers of information. Data and text will automatically adjust in size and detail.
Small file size, seamless and scalable with no distortion when zooming
What does GNSS comprise of
Generation system and is the combination of existing satellite navigation systems, with Satellite Based Augmentation Systems (SBAS) or Ground Based Augmentation Systems (GBAS)
GPS (NAVSTAR USA) and
GLONASS (Russia)
GALILEO (Europe)
BeiDou (china)
IRNSS (Indian Regional Navigation Satellite System)
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
Three things that affect gyro compass
Reliant on POWER! (Min 3hour spin up)
High speed
Sea state
Explain :
Safety depth and safety contour alarm
How they are trigged and uses
Safety depth is triggered by Eco sounder - used for UKC
Safety contour is triggered by GPS coordinates - used for navigation
What information would be included in Static information ?(AIS)
Identity (MMSI, Call sign, Name, IMO number)
Size
Type
Describe the principle operation of a fluxgate compass
Two soft ferromagnetic cores wrapped in a primary coil and a secondary coil around both.
AC current then excites the primary coil which creates an oscillation magnetic field and then induces and AC voltage in the secondary coil.
By turning the vessel in a complete circle a number of time the compass senses the earths magnetic meridian by electronically modulating and filtering the changing voltage amplitude.
Methods of acquiring targets on ARPA
Manual Fully Automatic Automatic by area Guard zones Guard rings
Describe 2 Errors you may experience when using a depth sounder and the causes of each.
Density- An Acoustic signal will travel faster in more dense water.
Second Trace Echoes- in very deep water it may occur the time taken between a pulse travelling to the seabed and back is greater than the time between pulses. Depth reading muck less than correct depth.
4 types of AIS messages that can be transmitted ?
Static - information does not change MMSI, Name, Call sign, IMO, Dimensions (6 minutes)
Dynamic - information automatic updated (GPS,GYRO or manually update (underway, RAM etc)
Voyage related - last port of call, route, ETA, Draft
Short Safety message - manually entered
What precautions should be taken when horizontal datum on the chart is ill defined?
Refer to Traditional forms of navigation. Use all available means
Explain how it is possible for a speed log to measure distance
A log that measures speed over ground can measure distance
What is SENC
System Electronic Navigational Chart.
A database resulting from the transformation of the ENC for ECDIS for appropriate use
Objective of AIS?
Range?
Uses what signal ?
(SOLAS, NAVIGATION, SECURITY, ENVIRONMENT.)
To enhance the safety of life at sea
Safety and efficiency of navigation
Security of vessels and port facilities and the protection of marine environment
20 - 30 M
VHF
With respect to the magnetic compass: a. Define the term ‘deviation’.
Angle between compass and magnetic heading.
SOTDMA
SELF ORGANIZING TIME DIVISION MULTIPLE ACCESS
Explain the difference between class A and B (AIS)
Transmitting strength?
Range?
A= uses SOTDMA (Self-organizing time-division multiple-access) Has the ability to turn of class B
Transmitting strength - 12.5W
Range - max VHF range 30+M
B = uses CSTDMA (carrier-sense time-division multiple-access)
B cannot turn off A
Transmitting strength -2W
Range - 8-10M
Explain how a Loran C receiver can distinguish between master and slave stations
9 Pulses for Master
8 Pulses for Slave
GPS shows HDOP 4, what does it mean?
Horizontal Dilution of Precision value of 4.
HDOP is expressed as a value between 1 and 8,
1 being the best 8 being the worst.
Value multiplied by 33meters gives overall 95% probability error.
Example HDOP 4
33x4 =134 meters
95% probability error is 134meters
Frequency used for Loran C and its typical range?
Frequency 100KHz
Range 800-1200 miles
Where can values of Variation be found?
Centre of each compass rose printed on large and medium scale Admiralty Charts
On Small Scale Admiralty charts lines are drawn across the chart joining places with the same variation. Know as Isogonic Lines
Attenuation
Weakening of a signal over distance
Principle of Radar
Distance time speed calculation
Transmission of a pulse of electromagnetic energy
The detection of the returning echoes
and the determination of range by measuring the time interval between transmission and reception
Speed x time divided by 2
What is the disadvantage of a fully automatic target acquisition?
Acquires unwanted targets that can clutter the screen.
When in the middle of the ocean how can you check your position ?
Compass checks via azimuth and amplitudes of the sun
Components of GPS?
Define each one
EDIT
Space
Consists of between 24 and up to 8 spare satellites in 6 orbits
Control
Consists of 5 land earth stations which constantly track satellites and determine there position
Colorado is the Main control station.
User
On board installation
Which typically consist of antenna, receiver and decoding unit
What is meant by the term Variation?
The angle between the direction of True North and the direction of Magnetic North. It is expressed as either East or West
Briefly describe setting up of Radar
Stand-by On Brilliance Gain Tune Clutter Sea and Rain Range
Difference between True Motion Ground stabilized and Sea Stabilizes (Radar)
If course made good and track is input it is said to be ground stabilized.
CMG and track input = ground stabilized
If course steered and speed through water is input the display is said to be sea stabilized.
course steered and STW is input = sea stabilized
What does a vessel need to be paperless
2 full independent ECDIS systems with independent backup power supply’s
Full ENC/VECTOR chart coverage and publications for the WHOLE voyage to the IMO standard - S52,S57,S63
What are the 2 properties of a gyro allow it to be used as a north seeking gyro compass
Rigidity
Precession
Difference between Relative and True Motion (Radar)
Relative- own vessel remains in the middle of the screen, motion of targets is relative
True- Own vessel tracks across the screen, motion of targets indicates their real movement
Principle operation of a fish finder
Sound waves transmitted and reflected echoes deteted by receiver.
Depth = VxT divided by 2
V(speed of sound in water)
T( Time from transmission to reception)
How does a Loran C receiver differentiate between different Loran C chains?
Each station within a group repeats its transmission at a fixed time interval. This is known as Group Repetition Interval
What is rate aiding and why is it important? (ARPA)
Tracking gates around a target that progressively reduce in size for a more precise prediction.
- Lowers likelihood of target swap
- Improves ability to track targets trough rain and sea clutter
Wavelength of X and S band
X 3cm - 9GHZ
S 10cm- 3GHZ
4 elements of passage planning with brief description of each
APEM
Apprasial
State of vessel, cargo, well rested crew, provisions, up to date charts and publications. Traffic. Pilot.
Planning
On the basis of the fullest possible appraisal, a detailed voyage or passage plan should be prepared which should cover the entire voyage or passage from berth to berth, including those areas where the services of a pilot will be used.
Plot on chart and ECDIS - communicated with all watch keepers.
Safe speed, UKC, contingency plans, the method and frequency of position fixing, including primary and secondary options
Execution
Having finalized the voyage or passage plan, as soon as time of departure and estimated time of arrival can be determined with reasonable accuracy, the voyage or passage should be executed in accordance with the plan or any changes made there to.
Reliability and condition of the vessel’s navigational equipment
ETD ETA and critical time periods for tide
Meteorological conditions (including day/night time)
Traffic conditions
Monitoring
The plan should be available at all times on the bridge
The progress of the vessel in accordance with the voyage and passage plan should be closely and continuously monitored.
Any changes made to the plan should be made consistent with these Guidelines and clearly marked and recorded.
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)
State the wavelength and frequency of the X-band and S-band radars
4 marks
X band 3cm 9GHZ
S band 10cm 3GHZ
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.
Radar Setup
Antenna is clear no Permits
Turn on / Standby
Brilliance - set to time of day
Range - selection/default 12M
Gain - light speckle/snow
Tune - Auto
Clutter - Sea/rain set for conditions
X Band positives and negatives
Positive
Small target detection
Range and bearing discrimination
AIS SART
Negative/poor
Detection long range
Detection in rain
S band positive and negatives
Negatives
Small target detection
Range and bearing discrimination
No AIS SART
Positive
Detection in rain
Detection long range
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
Where do they mount a transducer
1/3 along the hull
On centre line
Away from any sources of disturbance
Brief explanation of Appraisal in passage planning
APEM
Gather all information related to the voyage
Apprasial
State of vessel, cargo, well rested crew, provisions, up to date charts and publications. Traffic. Pilot.
Brief description of the planning stage of passage planning?
Planning
Lay out of the voyage
On the basis of the fullest possible appraisal, a detailed voyage or passage plan should be prepared which should cover the entire voyage or passage from berth to berth, including those areas where the services of a pilot will be used.
Plot on chart and ECDIS - communicated with all watch keepers.
Safe speed, UKC, contingency plans, the method and frequency of position fixing, including primary and secondary options
Brief explanation of the execution part of passage planning
Execution
Having finalized the voyage or passage plan, as soon as time of departure and estimated time of arrival can be determined with reasonable accuracy, the voyage or passage should be executed in accordance with the plan or any changes made there to.
Reliability and condition of the vessel’s navigational equipment
ETD ETA and critical time periods for tide
Meteorological conditions (including day/night time)
Brief explanation of the monitoring part of passage planning?
Monitoring
Monitor the passage plan by all available resources
The plan should be available at all times on the bridge
The progress of the vessel in accordance with the voyage and passage plan should be closely and continuously monitored.
Any changes made to the plan should be made consistent with these Guidelines and clearly marked and recorded.
List 6 factors in determining a safe speed (by all vessels)
(i) the state of visibility;
(ii) the traffic density including concentrations of fishing vessels or any other vessels;
(iii) the manoeuvrability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions;
(iv) at night the presence of background light such as from shore lights or from back scatter of her own lights;
(v) the state of wind, sea and current, and the proximity of navigational hazards;
(vi) the draught in relation to the available depth of water.
VD MAKE LITTLE WILLIES DROP
List 6 factors in determining a safe speed (additionally by vessels with an operational radar)?
(i) the characteristics, efficiency and limitations of the radar equipment;
(ii) any constraints imposed by the radar range scale in use;
(iii) the effect on radar detection of the sea state, weather and other sources of interference;
(iv) the possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;
(v) the number, location and movement of vessels detected by radar;
(vi) the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.
CHARLIE CARR EATS PIE NO MORE
Define the term SCAMIN
Scale minimum (SCAMIN) function is user defined and can be set as per the user need
A vessel which detects by radar alone (restricted Visibility) the presence of another vessel shall determine if a close- quarters situation is developing and/or risk of collision exists. If so, she shall take avoiding action in ample time, provided that when.
During Restricted visibility such action consists of an alteration of course, so far as possible the following shall be avoided:
RULE 19 D
(i) an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken;
(ii) an alteration of course towards a vessel abeam or abaft the beam.
Explain why ranges are more accurate than bearings when plotting a ships position (5marks)
Bearings suffer from half-beam width error.
When the edge of the beam strikes an object it paints an echo on the radar display, but due to the width of the pulse this is not the centre line of the beam which the bearing measurement should be take from.
Ranges are not effected by this
Explain where an echo sounder should be sited?
(1/3) aft of the bow on the centre line
Free from the effects from propulsion and cavitation.
On the center line to reduce the effects of pitch and roll
Away from the speed log to avoid interference
Echo sounder echos or spurious returns
Aeration/cavitation
Density
Temperature
Pythagorean error
Multiple echos - returns back and forward showing levels of deeper depths at the same distance
Second trace errors - shows depth shallow on a faint line
False errors
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.
Briefly describe DGPS
DGPS further enhances the local accuracy.
A ground based station knows its own precise location and compares it to the gps position - any errors are calculated and changed.
This DGPS position is transmitted from ground station to satellite and user via VHF signal so is only available within range (30M +/-)
E/Loranc errors
Base line errors (area behind the stations) they try to put these over land
Diamond error - when two Lines of Position have a poor angle of cut.
Describe the Doppler shift principle
A change in frequency as an object moves towards or way from the perspective of the receiver.
If we know the wavelength emitted then any change in frequency can be measured as speed
Differences between ECDIS and ECS
ECDIS
- is an officially approved navigation and information system
Hardware, software charts and back up facilities meet internationally agreed standards IMO
ECS
Not approved by IMO
Can be displayed on a device the is not officially approved for use when navigating IMO
ECDIS standards
S-52 provides specifications and guidance regarding the issuing and updating of ENC and their display in ECDIS this is within conjunction with IMO performance standard. (Standard colors and displays, seamless, alarms/indications, MSI.)
S-57 is used for digital exchange between hydrographical offices and to issue digital data to users
Cumulative notices
Twice a year January and July
It contains all the corrections for the previous two years
Allows you to check for previous corrections that may have been missed
How may a magnetic compass adjustor correct for the errors caused by the ships hard iron components
longitudinal and athwartships correctors
HE correctors
4 compass checks before departures
Fluid Lubber line is there No bubbles Numbers are clear to read Compare to repeater
State when the OOW should check the compass error
During every watch
After large alterations of course
How may a magnetic compass adjustor correct for the errors caused by the ships soft iron components
Kelvin spheres
Flinders bar
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.
Passage planning reference guides
STCW chapter 8
MGN 166
Bridge procedures
Vessels that can use inshore traffic zones
Vessels < 20m Vessels engaged is fishing En route to or from a port Offshore installation or structure To avoid immediate danger
MLC hour of rest
10 hours in 24 hours
No more than two rest periods, with period of 6 hours uninterrupted
77 hours of rest per 7 day week
What makes up an approved ECDIS
Should use official chart data S-57 Allow regular updating Display the standard S-52 Support the full range of navigation option Can continually plotting ships position
When are paper charts required?
When the vessel doesn’t have two fully independent ECDIS systems with two separate power supply’s
What is integrity monitoring
Is consistently checking the system is displaying the correct information. This can be done through.-
Position fixing Echo sounder Compare gyro and mag compass Radar overlay ARPA overlay on chartered features Track history
When would an echo sounder show less the actual depth
Second trace echo
Side Echo
Density
ECDIS carriage requirements
New passenger vessel over 500GT
Cargo ships of 3000GT
explain difference between safety depth and safety contour
Safety contours are set by the user and can be seen as a blue line/contour line
Safety depth are also set by the user and are show in BOLD can be set deeper/or shallower than safety contour
