Nav & Radar MCA 100 past questions Flashcards
List 5 Nautical publications needed for passage planning. And what they contain
- Chart Catalogue. Starting point for passage planning. Gives full details of charts and publications needed for your voyage in a world wide inventory
- Ocean Passages of the World. Used for ocean passages detailing weather, currents, ice, hazards and distance between major ports
- Mariners Handbook. Can be used as a guide to improve understanding of metrology, Navigation and regulations.
- Admiralty Sailing Directions
- Admiralty List of Radio Signals. Provides all information on all aspects of maritime radio.
- Admiralty List of Lights and Fog Signals
- Routeing Charts. Wind direction + speed, ocean currents, sea + air temperatures, air pressure and frequency of storms.
- Tidal Stream Atlas. Used to predict direction and speed of tidal currents
- Notices to Mariners. Corrections to nautical charts and publications
What are the benefits of ARPA?
- Reduces workload
- assist with data interpretation; target tracking is automatic.
- Provides continuously updated info and rapid situation evaluation
- should, if used correctly, reduce the risk of collision.
List six things ARPA must show.
- Range of Target
- Bearing of target
- Predicted CPA
- Predicted TCPA
- True Speed
List 5 ECDIS alarms.
- Crossing safety Contor
- Approach to a critical point
- Deviation from route
- Position system failure
- Different geodetic data
5 ECDIS warning indicators?
- Default safety contour
- Information over scale
- Larger-scale ENC available
- No ENC available
- System test failure
- Area with special conditions
Describe spring tides and Neap tides
- Spring tide is when the planetary bodies are in alignment. Giving higher high tides and lower low tides.
- Neap tides are when the planetary bodies are not in alignment. Causing lower high tides and higher low tides
What’s the difference between relative and true motion radar display?
- Relative motion is the standard default display. Shows relative vectors. Good for collision avoidance.
- True motion shows true vectors of vessels. Shows true heading of targets
What’s the difference between RCDS, ECDIS and ENC
- ECDIS is a highly sophisticated nav system that meets IHO and IMO standards for navigation.
- ENC is a vector chart data produced by the national hydrographic office that does not meets IMO and IHO standards
- RCDS = Rasta chart display system is a scanned paper chart. It’s a mode of operation in ECDIS
What factors should be taken into account when determining safe speed?
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- state of Visibility.
- the traffic density, including the concentration of fishing vessels and other vessels.
- manoeuvrability of the vessel.
- at night, the presence of background light.
- weather. The state of wind, sea and current and proximity of nav hazards.
- Draft of the vessel.
Safe speed part 2 - What are the additional factors with the operation of a radar to take into account?
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- The characteristics, efficiency and limitations of the radar
- Any Constraints imposed by the radar ranges scale in use
- Effects on the radar detection of sea state, weather and other sources of interference.
- The possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range.
- The number, location and movement of vessels detected.
- More exact assessment of the visibility may be possible.
What are the four stages of passage planning?
Appraisal - gather information about the passage. Charts and publications needed for the route.
Planning - identify all the danger areas, hazards, intended track from berth to berth, Safest and fastest route, waypoints reporting points and PI. Record the plan in the bridge notebook.
Execution - briefing the bridge team in the passage plan and navigating the ship accordingly. Berthing and logistical information, environmental factors, ETA’s at critical points considered.
Monitoring - checking progress of the ship against the passage plan. Navigation equipment checked regularly as well as any changes amended and compliance with IRPCS and MARPOL regulations.
What compulsory Inputs are needed for ECDIS?
- GPS
- Speed Log
- Gyro Compass
What are the Advantages and disadvantages of ENC?
Advantages
- Alarms
- Easy to update
- Set contours and safety depths
- Display orientation. set north up or course up
-Smaller files
-Layers of information
- Zoom in and out and symbols stay the same
Disadvantages:
- Cost
- Hidden information
- Limited coverage worldwide
What RCDS pros and cons?
Pros:
- worldwide coverage
- affordable
-similar to Pape charts
Cons
- No alarms
- No customisation
- Large files
- Small Zoom
- expensive to correct
- When you change charts, you need to check you are using the correct datum
Principles of an Echo Sounder
- Transducer sends a pulse of sound to the sea floor at 1500m per second
- Return pulse moves coils and creates voltage. The time interval between them is calculated
- Depth processed and displayed
- Depth = velocity x time/2
What are multiple echos on an Echo sounder?
- Multiple echos may bounce between the hull and sea bed a number of times at each return; some of the energy can be detected. Most noticeable in shallow water
Echo Sounder Errors
- False echos
- Cone effect
- Side reflection - side lobes from embankments
- Aeration - air bubbles
- Propagation - speed that sound travels through water changes with temperature and salinity
- Noise
- Pythagoras - when TX and RX are not in a single transducer
What are the two standard frequencies for an echo sounder?
- 200 KHz - shallow, narrow cone, defined image
- 50 KHz - deep, wide cone, less defined
What’s the Principle behind GPS?
- A satellite generates a radio wave signal at the speed of light with accurate time stamp
- At the same time a GPS receiver generates identical code and compares time difference upon receiving the signal
- A range is then calculated
- Range = Speed of light x Time
What are the three main components of GPS?
Space segment - consists of 24 satellites and six spares. There should be a minimum of 4 satellites at all times
Control segment - a series of worldwide ground control stations for monitoring and tracking.
User Segment - The user segment only receives. (You on the boat)
What’s differential GPS (DGPS)
Uses bases with a fixed known position to adjust real time GPS signals to eliminate errors
- Base station receives signal from GPS
- Calculate the error from a known position.
- Works out time error and sends it to users
Define DOP.
Dilution of Precious is a way to measure the quality of the GPS fix. Dop 1 indicates a good fix, and Dop 4 indicates a poor one.
What is HDOP?
Horizontal Dilution of Position: gives you Lat and long and is needed for the position
List five GPS errors.
- Ionosphere error: caused by ironized partials in the upper atmosphere that can slow the signal down.
- Troposphere error: caused by weather.
- Multi-path error: caused by mountains, buildings, and bridges can cause the signal to reflect.
- Sat clock error: accurate time on board is essential.
- Receiver noise: interference from radio transmission can affect the signal
Explain Geo datum and datum shift?
- Geo Datum is a mathematical model of the surface of the earth.
- Datum shift is the distance to move a fix rendered to WGS84 to place it on a chart correctly.
What’s the difference between true motion and relative motion?
- True motion displays the actual vectors of the target and observing vessel.
- Relative motion display portrays the motion of the target relative to the motion of the observing vessel
How does a Doppler Log work?
The Doppler log transmits an acoustic sound through the water at a 60-degree angle. The horizontal signal that is reflected will have a higher frequency the faster the vessel moves forward and a lower frequency the slower it goes. This is a Doppler shift and can be converted to speed.
What are the Advantages of a Doppler Log over an Electromagnetic Log?
- Yields STW and SOG
- Not susceptible to hull shape irregularities
- Better in pitching and rolling
- Better at speed, berthing and reversing
- No moving parts
- Highly accurate
How does the Doppler log overcome pitching and rolling?
Janus Configuration - Has two transducers, one facing forward and one aft about 60 degrees. The effect is to cancel errors when pitching and rolling.
What should you do when approaching restricted visibility?
- Inform the master
- Increase lookouts
- Appropriate nav lights
- Appropriate sound signals
- Fix position
- Reduce to safe speed
- Engines on standby
- Radar plotting
- VHF 16 and 13
- Hand steering
What are the Advantages of a Doppler log over an EM log?
- Yields STW as well as SOG.
- Not susceptible to hull shape irregularities.
- Better in pitching and rolling.
- More resistant to fouling and aeration.
- Better at low speed and berthing/ reversing.
What are 4 Doppler Log errors?
- Propagation speed determined my sea temperature and salinity.
- Damaged unit.
- Heavy pitching and rolling.
- Aeration caused by engines and thrusters.
What are the types of marks used in the IALA buoyage system?
- Safe water marks
- Isolated danger marks
- Special markers
- Cardinal marks
- Lateral marks
- Emergency wreck marks
What’s the difference between IALA A and B?
The two systems are the same, except that the colours of the lateral marks are reversed. CAN always on PORT and CONE always on STARBOARD.
How do you reduce the errors caused by deviation?
Permanent magnetism - Longitudinal and athwartship magnets are placed inside the compass binnacle
Induced Magnetism - Soft iron spheres (Kelvins balls) and flinders bar magnets are used
What is deviation?
The ship’s metals and iron cause the compass needle to deviate from magnetic north. The angular difference is called deviation.
Pros and cons of X-band radar?
- Better range and bearing discrimination
- Better at picking up targets
- Picks up SARTs
- 3cm beam width
- 10 GHz frequency
- More sea clutter response
- Not good in precipitation
- Not good for long-range
Pros and cons of S-Band Radar
- Better in bad weather
- Better for long range
- 10cm wavelength
- 3GHz Frequency
- Doesn’t pick up Sarts
- Poor range and bearing discrimination.
What is sea clutter?
Sea clutter suppresses gain in the centre of the radar. It never extends the whole range. Reducing effects out to 4 to 6NM
How does Rain clutter work?
- It acts on the echo by trying to cut off the trailing edges so that just the leading edge is seen. Applies this to the whole range of display