Nav Equipment Flashcards
What is MGN 610
Guidance on the Merchant Shipping Safety of Navigation Regulations 2020.
(National legislation of SOLAS Ch V.)
Required Nav equipment on SOLAS Ship
(17)
Magnetic Compass
Gyro Compass
Means of taking a bearing
Means of converting heading and bearing to true (deviation card)
Echo Sounder
GNSS receiver (GPS)
Log
Rudder Angle Indicator
Radar (both 3 & 9 GHz)
ECDIS
AIS
Signalling lamp
Met Instruments
Search Lights
EPIRB
SART
BNWAS
LRIT
Nautical charts and publications
other:
Transmitting heading device
Talkback system
Audio detection device.
GPS, how does it work?
Satellite based navigation system. (US Government)
-24 satellites
-Broadcasts:
1. Satellites own location
2. Time signal was transmitted
- 4 satellites needed for position (+/- 5m)
HDOP
Horizontal dilution of precision
2D aspect of total error in terms of lat and long.
Low number= good fix
High number= poor fix
What is SBAS
Satellite Based Augmentation System
DGPS correction data
-Geostationary satellites provide corrections to specific areas
-Improves positional accuracy
Errors of GPS
-Solar Activity on the Ionosphere: charged electrons change speed and direction of signal between Sat and Receiver.
-GPS Jamming
-Tropospheric Errors: Water vapour in atmosphere
-Satellite orbit errors: drift of satellite
-Satellite Clock errors
-Multi path errors : GPS receivers should be mounted as low as possible to avoid this
How does an Echo Sounder work?
Short pulses of sound vibrations
Sound waves are reflected off seabed
Time measured between transmitted and receiving
Speed of sound in water = 1500m/s
Therefore : D = S X T (DIVIDED BY 2)
Errors of Echo Sounder
(7)
- False Echoes
- Aeration and cavitation
- Shallow Water Effects
- Water Density
- Second Trace echoes
- Multiple echoes
- Parallax error
False Echoes
-Echo Sounder Error
(6)
- Shoals of fish
- layers of water with differing speeds of sound
- submarine springs
- seaweed
- turbulence from tidal streams
- echo reflections from ships hull when in shallow water
list the 4 types of logs and whether they measure STW or SOG
Logs: Ground and Water Track
Impeller or Paddle Wheel Type (STW)
Pitot Static Log (STW)
Electromagnetic Log (STW)
Doppler Log (STW and SOG)
Doppler Shift
‘State the law’
“The apparent change in the frequency of a wave caused by the relative motion between the source of the wave and the observer.”
What is the name of the SBAS system over the UK
EGNOS
What is RAIM
Receiver Autonomous Integrity Monitoring
technology developed to assess the integrity of individual signals received by the GNSS.
in built GPS test system
green:good
amber:medium
red:poor
How often should an echo sounder be checked and how?
Annually or when there is doubt about accuracy.
using a hand lead line
Settings of an echo sounder?
Depth below keel
Depth below waterline
Depth below transducer
Gyro failure?
CALL THE MASTER
Unable to easily take bearings to assess ROC, Position fixing + Steering issues.
Gyro feeds the Radar, it will revert to Heading mode.
Switch Autopilot to track control.
Log the defect.
GPS failure?
CALL THE MASTER
Will revert to DR mode.
Continue to plot position manually.
