Nav Equipment

Question 1

What is MGN 610

Answer 1

Guidance on the Merchant Shipping Safety of Navigation Regulations 2020.
(National legislation of SOLAS Ch V.)

Question 2

Required Nav equipment on SOLAS Ship

Answer 2

Magnetic Compass
Gyro Compass
Means of taking a bearing
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

Question 3

GPS, how does it work?

Answer 3

Satellite based navigation system. (US Government)
-24 satellites
-Broadcasts:
1. Satellites own location
2. Time signal was transmitted
- 4 satellites needed for position (+/- 5m)

Question 4

HDOP

Answer 4

Horizontal dilution of precision

2D aspect of total error in terms of lat and long.
Low number= good fix
High number= poor fix

Question 5

What is SBAS

Answer 5

Satellite Based Augmentation System

DGPS correction data

-Geostationary satellites provide corrections to specific areas
-Improves positional accuracy

Question 6

Errors of GPS

Answer 6

-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

Question 7

How does an Echo Sounder work?

Answer 7

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)

Question 8

Errors of Echo Sounder

Answer 8

False Echoes
Aeration and cavitation
Shallow Water Effects
Water Density
Second Trace echoes
Multiple echoes
Parallax error
Shallow Water effects

Question 9

False Echoes

Answer 9

-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

Question 10

Logs: Ground and Water Track

Answer 10

Impeller or Paddle Wheel Type (STW)

Pitot Static Log (STW)

Electromagnetic Log (STW)

Doppler Log (STW and SOG)

Question 11

Doppler Shift

Answer 11

“The apparent change in the frequency of a wave caused by the relative motion between the source of the wave and the observer.”