MOCK Exams Flashcards
(74 cards)
1
Q
MOCK 1 Answers (Part B)
A
2
Q
RADAR
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3
Q
(a) Describe the foundation principle of how a range of a detected target is calculated by radar (2)
A
- 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
4
Q
(b) List the factors that affect the detectability of a radar target (5)
A
- 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
5
Q
(c) Describe the meaning of Range discrimination of a Radar (5)
A
Is the ability of the radar to detect target on different ranges but on the same bearing
6
Q
(d) Describe the meaning of Bearing discrimination of a Radar (5)
A
Is the ability of the radar to detect target on different ranges but on the same bering
7
Q
(e) Describe the cause and effect of blind and shadow sectors of a Radar (3)
A
- 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.
8
Q
COMPASS
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9
Q
(a) Define magnetic variation of a compass (2)
A
Is the angular difference between Magnetic nord and True Nord
10
Q
(b) What are the two types of deviation of a magnetic compass and what are their causes? (5)
A
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
11
Q
(c) What are the correctors used on a marine magnetic compass to reduce magnetic deviation? (3)
A
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
12
Q
(d) Explain why deviation changes with the ships head (3)
A
13
Q
(e) How often should the OOW check the compass error? (2)
A
- Pre-deperture
- Once a watch
- After every large alteration of course
14
Q
(f) How would you carry out a compass check onboard? (5)
A
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
15
Q
GPS
A
16
Q
(a) What are the three segments of the GPS system? (3)
A
- Space Segment - 24 satellite 6 orbit
- Ground Segment - 1 master (Colorato USA) 5 monitoring station near Equator
- User Segment - Any GPS receiver
17
Q
(b) Explain how a position is calculated using the GPS system (5)
A
- 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
18
Q
(c) Explain the term HDOP and when/where it might occur (5)
A
- Dilution of precision: The reliability of the data due to the geometry (azimut and elevation) of satellites in view of the receiver.
- Horizontal DOP -
19
Q
(d) What is the datum used with GPS? (1)
A
WGS 84 - Is the reference where the position is calculated from
20
Q
(e) Can you use a chart that references a different datum to that of the one being used on the GPS? (2)
A
Yes, if I have acces to the difference between the two datum
21
Q
(t) List the possible errors of the GPS (4)
A
- Satellite time error
- Satellite Orbit error
- Ionosphere Delay Error
- Troposphere Delay Error
- User Timer Error
- User Noise Error
- Multi-Path Error
22
Q
MOCK 4 Answers (Part B)
A
23
Q
ARPA
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24
Q
A) What does ARPA stand for? (2)
A
Automatic Radar Plotting Aid
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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.
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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
27
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
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E) Can ARPA be used for IRCPS? (2)
Yes, as long we are verifying the information are correct with other means.
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PARRALEL INDEX
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a) Describe the term “Parrallel Indexing) (3)
Tool to maintain cross track, error useful in Restricted Visibility and Narrow channel
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b) With the aid of a diagram show how P.I. lines are used (5)
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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
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d) Describe Radar setup you would use for navigation with P.I. Lines (4)
- North Up
- Relative Motion
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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
35
LORAN
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a) What frequency does the LORAN system operate on? (2)
100 kHz, low radio frequency radio.
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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
38
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)
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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.
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e) What is ELORAN (2)
- Enhanced LORAN.
- Use modern technology to increase accuracy of the system, correcting for known errors
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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
42
MOCK 5 Answers (Part B)
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GPS
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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
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B) How many satellites are there in the ‘space segment’ of the GPS system?
24 Satellite. 4 satellite in 6 orbits planes
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C) What does DGPS means
Differential GPS - It use difference in position from known object to minimise errors
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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
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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
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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.
50
MOCK 6 Answers (Part B)
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AIS
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A) What does AIS stand for? (1)
Automatic Identification System
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B) What Frequency does AIS operate on? (1)
VHF
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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
55
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
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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
57
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
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G) Can AIS be used for IRCPS? (1)
No, as rely on other vessel equipment, but can increase situational awareness
59
ECHOSOUNDER
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A) Draw a diagram of the key components of the marine echo sounder (4)
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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
62
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
63
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
64
IMPELLOR LOG
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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
66
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
67
MAGNETC COMPASS
68
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
69
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
70
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
71
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
72
E) Why does a Gyro compass require a GPS input? (1)
To correct for Lat Error
73
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
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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
