Navigation Equipment

Question 1

Magnetic compasses should be adjusted when:

Answer 1

• They are first installed.
• They become unreliable.
• The ship undergoes structural repairs or alterations that could affect its permanent
  and induced magnetism.
• Electrical or magnetic equipment close to the compass is added, removed or altered.
• A period of two years has elapsed since the last adjustment, and a record of compass.
• Deviations have not been maintained, or the recorded deviations are excessive.
• When the compass shows physical defects.
• Collision or major change of Latitude.

Question 2

True bearings are in relation

Answer 2

TO TRUE NORTH

Question 3

Magnetic bearings are in relation

Answer 3

to MAGNETIC NORTH and are affected by VARIATION but NOT deviation.

Question 4

Compass bearings are in relation

Answer 4

To MAGNETIC NORTH and are affected by BOTH variation and deviations

Question 5

Correcting compass bearings

Answer 5

• When correcting the compass bearing to true to lay off on the chart, variation and
  deviation must be applied in the correct order.

REMEMBER;

True Virgins Make Dull Company.

TVMDC
=>
West is BEST (+) , East is LEAST (-)

Question 6

Gyro compass finds true north as determined by

Answer 6

Earth’s rotation, which is different from, and navigationally more helpful than, magnetic north, and they are unaffected by ferromagnetic materials, such as ship’s steel hull, which change the magnetic field.

Hence you can plot a gyro bearing directly to a chart!

Errors/feeds of Gyro
1. SOG
2. Latitude

Question 7

What equipment relies on the gyro?

Answer 7

Radar
Sat C
Auto Pilot
ECDIS
AIS

Question 8

Means of taking a bearing?

Answer 8

The pelorus, which enables the navigator to obtain bearings of shore objects, is an
alternative to the azimuth mirror.

It is advantageous when the line of sight of the Azimuth mirror on the standard compass is obscured.

Being a portable instrument, it can be transferred from bridge wing to bridge wing so that such obstructions need never impede the line of sight as the funnel.

It is lined up fore and aft, and then it can give relative bearing from the ships head.

It has a graduated 360o compass card inside.

It provides relative bearings to the ships head.

Question 9

Azimuth circle gives bearing in relation to the

Question 10

Azimuth Mirror
- Point the arrow upwards to take bearing
- Point the arrow downwards to take a bearing

Question 11

Pelorus can give relative bearings, relative to the ships head and in relation to a compass course steered

Question 12

How do we check a compass?

Answer 12

There are numerous ways to check a compass:

• By a transit if in coastal waters.
• By Azimuth of a heavenly body via the ABC tables OR via the amplitude of the sun
  (the easiest and most convenient is the sun).
• By bearing of a distant object.
• By reciprocal bearings with another ship of known compass error.
• By reduction of the cocked hat.

Question 13

To find the Compass Error by Transit

Question 14

By the amplitude of the sun at rising or setting

Question 15

Remembering that at sunrise and sunset is ….

Question 16

How to check a compass via Azimuth of a heavenly body (anytime of day)

Question 17

GPS. How does it work ?

Answer 17

When a GPS set on board receives a satellite signal, it can calculate the range from the known satellite position by the time difference between signal transmission and receipt.

A satellite transmits a signal, which carries a particular code. The receiver generates this same code internally, starting at precisely the same time.

When it receives the code from the satellite, it can measure the difference between them.

Since radio waves travel at the speed of light, which is known, the range can be determined.

A clock inaccuracy of just one-millionth of a second would give a ranging error of about 400m.

Question 18

HDOP

Answer 18

“Horizontal dilution of precision”
is the two-dimensional aspect of total error in terms of Latitude and longitude.

Some receivers show HDOP with an accompanying number.

~A low number indicates a good fix, a higher number a poor fix.

ERRORS

Ian Eats Sweets Makes Teeth Rot
(Ionosphere, Ephemeris, Satellite clock, Multipath, Troposphere, Receiver noise.)

Question 19

E Loran

Answer 19

Recently in 2013, the General Lighthouse Authorities of the UK and Ireland (GLA) have announced that ships in the Port of Dover, its approaches and part of the Dover Strait can now use eLoran RADIO navigation technology as a backup to satnav systems like GPS and Galileo.

The GROUND BASED eLoran system provides alternative POSITION and TIMING signals for improved navigational safety.

Question 20

Logs ground and water track

Answer 20

Impeller or Paddle Wheel Type
~It may be hull-mounted or towed. The numbers of revolutions are proportional to the distance travelled through the water. Speed of rotation is proportional to the vessel’s speed.

Pitot-Static Log
~At rest, the pressure in both tubes is virtually the same. With motion, dynamic pressure in the pitot tube produces an increased total pressure, resulting in movement of the diaphragm.

Electromagnetic Log
~The electromagnetic log operates on the principle that an electrical voltage will be produced in a conductor if moved through a magnetic field.

Doppler Log
The Doppler (or ground reference) log sends a signal downwards similar to an echo sounder and receives it back, reflected either from the sea bed (if is it not too deep) or from a water layer of different density.

The actual speed is computed from the Doppler Shift:
It’s the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.

Question 21

AIS

Answer 21

AIS is a maritime mobile VHF broadcast system that can send both dynamic and static ship information, such as MMSI, call sign, position, course and speed, to other AIS transponders and base stations.

Therefore, the purpose of AIS is to help identify vessels, assist in target tracking, simplify information exchange (e.g. reduce verbal mandatory ship reporting), and provide additional information to assist situation awareness.

Question 22

ENC Symbols

Question 23

Where would you find the carriage requirements for navigation equipment

Answer 23

SOLAS Chapter V - Regulation 19
Carriage requirements for shipborne navigational systems and equipment