MOCK Exams Flashcards
MOCK 1 Answers (Part B)
RADAR
(a) Describe the foundation principle of how a range of a detected target is calculated by radar (2)
- Radar send PULSE by the Transmitter at the speed of light (300,000,000 m/s)
- Pulse attenuates as it moves trough space
- Pulse strikes a TARGET
- ECHO return to receiver
- Echo is received by ANTENNA
- Contact is seen on a radar DISPLAY
- Range is speed X time divided 2
(b) List the factors that affect the detectability of a radar target (5)
- Material - Steal work better then other
- Aspect - Only perpedicular surface surface will return Echos
- Size - Bigger is the target better change you have a return of
- Texture - Ruff surface will have more likelihood to be hidden by a echo
- Shape - Cubes are better than spheres when perpendicular to the scanner
(c) Describe the meaning of Range discrimination of a Radar (5)
Is the ability of the radar to detect target on different ranges but on the same bearing
(d) Describe the meaning of Bearing discrimination of a Radar (5)
Is the ability of the radar to detect target on different ranges but on the same bering
(e) Describe the cause and effect of blind and shadow sectors of a Radar (3)
- 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.
COMPASS
(a) Define magnetic variation of a compass (2)
Is the angular difference between Magnetic nord and True Nord
(b) What are the two types of deviation of a magnetic compass and what are their causes? (5)
Permanent deviation
- Is the entire influence on the compass from all the combined part of your vessel sach us: Engine, Generators, Ancor, Hull, Ecc.
induced deviation
- Build of a charge from the heart magnetic field accumulating in any ferrous material of the vessel
(c) What are the correctors used on a marine magnetic compass to reduce magnetic deviation? (3)
Permanent Deviation
- Addition of longitudinal and transversal correcting magnets
Induced Deviation
- On marine compasses is corrected using soft Iron Kelvins Balls and Flinders.
- If the vessel has an aft bridge the bar need to be fit forward and for a forward bridge the bar would be fitted aft
(d) Explain why deviation changes with the ships head (3)
(e) How often should the OOW check the compass error? (2)
- Pre-deperture
- Once a watch
- After every large alteration of course
(f) How would you carry out a compass check onboard? (5)
Transit
In pre-departure, If you’re Square dock along side compare our heading to the alignment to the dock
Charted known bearing
Sun azimut
GPS
(a) What are the three segments of the GPS system? (3)
- Space Segment - 24 satellite 6 orbit
- Ground Segment - 1 master (Colorato USA) 5 monitoring station near Equator
- User Segment - Any GPS receiver
(b) Explain how a position is calculated using the GPS system (5)
- Satellite transmit signal with Time and Position
- Receiver receive the signal
- Receiver know the start time
- Receiver workout the time difference and calculate the range from the satellite
(c) Explain the term HDOP and when/where it might occur (5)
- Dilution of precision: The reliability of the data due to the geometry (azimut and elevation) of satellites in view of the receiver.
- Horizontal DOP -
(d) What is the datum used with GPS? (1)
WGS 84 - Is the reference where the position is calculated from
(e) Can you use a chart that references a different datum to that of the one being used on the GPS? (2)
Yes, if I have acces to the difference between the two datum
(t) List the possible errors of the GPS (4)
- Satellite time error
- Satellite Orbit error
- Ionosphere Delay Error
- Troposphere Delay Error
- User Timer Error
- User Noise Error
- Multi-Path Error
MOCK 4 Answers (Part B)
ARPA
A) What does ARPA stand for? (2)
Automatic Radar Plotting Aid
B) Describe how the ARPA work (5)
- Arpa is an automated aid of Radar plotting OAW.
- The target is acquired (Manually or Automatic or in Guard Zone)
- The target goes in the Box acquisition phase. ARPA return range and bearing
- After 3 minute the ARPA will steady tracking the target.
C) What information does ARPA Provide to the Watch-keeper
Range and bearing
CPA & TCPA
Calculate Course and Speed
Bow Crossing Time Bow crossing distance
D) What effect would a faulty heading and/or speed input have on the information read out from the ARPA (6)
It would return a faulty reading on the OWA
W-O and W-A would be a false reading from the Gyro
W-O only would be a false reading from the Log
E) Can ARPA be used for IRCPS? (2)
Yes, as long we are verifying the information are correct with other means.
PARRALEL INDEX
a) Describe the term “Parrallel Indexing) (3)
Tool to maintain cross track, error useful in Restricted Visibility and Narrow channel
b) With the aid of a diagram show how P.I. lines are used (5)
c) List some Objects which would be suitable and not be suitable to reference with P.I. (4)
Good
- Land (cliff)
- Brake water
- Radar Conspicuis point
Bad
- Drying height
- Buoys
- Moving object
- Boats
d) Describe Radar setup you would use for navigation with P.I. Lines (4)
- North Up
- Relative Motion
e) Describe the use of Radar overlay and when it may be used (4)
- Radar can be set over ECDIS
- We can see GPS error where the overlay of radar does not match the feature on ECDIS
LORAN
a) What frequency does the LORAN system operate on? (2)
100 kHz, low radio frequency radio.
b) Briefly describe how a position is calculated using the LORAN system (5)
- Use time differences between 2 different pulses from 2 different station to get one line of position
- Then use the time difference of another 2 station sending 2 different pulse and get another line of position.
- With two line of position you can fix a position
- From the center of the towers and close to those, you have a better angle of cut and a more precise position fixing
c) What is the approximative range of LORAN for both, ground and sky wave (2)
- Ground Wave - 600 to 800 NM (Depend on atmospheric condition)
- Sky Wave - 1200 to 2000 NM (Depend on ionization)
d) What are the Errors of the LORAN System (4)
2 Fix:
- Land Error - Land slows the propagation of the pulse
- Dimond Error or Base line extension - the area where the hyperbolic curve are more bended
2 Dynamic:
- Clock error
- Sky wave rejection from the Ionosphere.
e) What is ELORAN (2)
- Enhanced LORAN.
- Use modern technology to increase accuracy of the system, correcting for known errors
f) What are the advantages and disadvantages of LORAN against GPS? (5)
Pros
- Doesn’t rely on satellite
- Land Based
- Can be done in Local area (Don’t need to be Global)
- A good backup to GPS
- Don’t have to rely to Sextant
Cons
- Not always accurate
- High maintenance cost
- No world wide coverage
- Largely discontinued
MOCK 5 Answers (Part B)
GPS
A) How many satellite are require to gain a position from the GPS System
- 3 satellite for a 2D positon
- 4 satellite for a 3D position
B) How many satellites are there in the ‘space segment’ of the GPS system?
24 Satellite. 4 satellite in 6 orbits planes
C) What does DGPS means
Differential GPS - It use difference in position from known object to minimise errors
D) Explain how DGPS works
- DGPS use the differential in position from station known position and the GPS position reading
- Calculate the range from the two
- GBAS will transmit a GPS pulse to DGPS receiver with correct data.
- SBAS will transmit the pulse to Sat-C satellite and those will revert the signal to receiver
- The receiver use this to correct his own GPS receiver
E) List errors in GPS System
- Satellite clock error
- Satellite Orbital error
- Ionosphere Delay error
- Troposphere delay error
- Receiver clock error
- Receiver noise Error
- Multi Path error
F) Describe any two GPS errors
- Satellite clock error - drift in the satellites ceasium clocks allows errors of up to 1.5 metres
- Satellite Orbital error - errors creep in between updates of the almanac of data
- Ionosphere Delay error - A different ionization of the ionosphere particles can bend/disturb the signal traveling from the GPS to the Receiver
- Troposphere delay error - area of earths atmosphere at different temperature and pressure which causes very small errors
- Receiver clock error
- Receiver noise Error - interfering radio transmissions
- Multi Path error - mountains, buildings, bridges and other vessels can reflect the signal causing more than one signal.
MOCK 6 Answers (Part B)
AIS
A) What does AIS stand for? (1)
Automatic Identification System
B) What Frequency does AIS operate on? (1)
VHF
C) List items that would be on a class A AIS dynamic data transmission (5)
Transmitted every 2” to 10”
- Vessel position
- COG & SOG
- Rate of turn (ROT)
- Navigation Status
- True heading
D) List items that would be on a class A AIS static data transmission (5)
Transmitted every 6 minutes
- Name
- Call Sign
- MMSI
- Type of vessel
- Length
- Breadth
E) List items that would be on a class A AIS Voyage data transmission (4)
Transmitted every 6’
- Destination
- Previous port
- ETA
- Person on board
- Type of Cargo
- Draught
- Navigational status
- can send short securite messages
F) What does the term “SOTDMA” means and how does it work (3)
- Self Organise Time Division Multiple Access
- Is a system that pre allocate Class A AIS future transmission slot
G) Can AIS be used for IRCPS? (1)
No, as rely on other vessel equipment, but can increase situational awareness
ECHOSOUNDER
A) Draw a diagram of the key components of the marine echo sounder (4)
B) How would multiple echoes appear on an echo sounder display and when would they be most luckily to occur? (3)
- Will appear in shallow water when using the too high frequency
- where seabed are more reflective
C) Where on a ship should a transducer be located? (2)
- Need to be located amidship, about at 1/3 from the bow, close to the center line, away from possible interference (turbulence, electrical) and troughs-hull opening
D) Describe the setup of an echo sounder up for the best performance in shallow water and deep water ? (4)
- 50 KHz would be better for deeper water as will use a longer pulse length and this will travel further than a shorter pulse and use a wider cone
- 200 KHz would be better for shallow water uses short pulse and the cone is narrower
IMPELLOR LOG
E) Explain how speed is calculated from an impellor log (3)
- A impeller will rotate with the water flow
- a pick-up sensor will count the every impeller turn with the magnet on it
- As this rotation is a know ratio distance, we can calculate the distance (from the rotation) x Time, we get the speed
F) What are the advantages and disadvantages of an impellor log (4)
Advantages
- cheap
- Simple
- work at slow speed
- is retrievable
Disadvantages
- Suffer for marine growth
- Need regular check for accuracy
- Easy to brake
MAGNETC COMPASS
A) List 5 Circumstances when the magnetic compass should be checked and adjusted (5)
- On build
- Every 2 years
- Major items added or removed
- Works onboard the vessel such us welding
- Fire or damage onboard
- Whenever is notice an error or the deviation car are not correct
- Major change in latitude
- Vessel is long time alongside
B) What are the causes of permanent deviation and how are they corrected for in a marine compass? (3)
- Is the entire influence on the compass from all the combined part of your vessel sach us: Engine, Generators, Anchor, Hull, Etc.
- Addition of longitudinal and transverse correcting magnets placed in compass binnacle
C) What are the causes of induced deviation and how are they corrected on a marine compass? (3)
- Build of a charge from the heart magnetic field accumulating in any ferrous material of the vessel
- On marine compasses is corrected using soft Iron Kelvins Balls and Flinders bar.
- If the vessel has an aft bridge the bar need to be fit forward and for a forward bridge the bar would be fitted aft
D) Is a Marine Gyro compass affected by variation or deviation? (2)
- No as the true nord is obtained by the principle of gyroscopic proprieties
- Gyro can have errors but will be of a different nature than Magnetic
E) Why does a Gyro compass require a GPS input? (1)
To correct for Lat Error
F) How does a GPS compass work? (2)
Recipe a signal from a satellite to 3 antennas and compares the location in relation to each other
G) What are the advantages and disadvantages of the GPS compass? (4)
Advantages
- Cheaper than a Gyro
- Not effected by Magnetism (Variation and Deviation)
- No moving parts
- No effected by Lat Error
- Work better at higher latitude
Disadvantages
- Rely on GPS
