Navigation Instruments

Question 1

What Navigation Instruments can be used from the Bridge?

Answer 1

• Azimuth Mirror
• Sextant
• Gyro/Magnetic Compass
• ECDIS

Question 2

How to take bearings of Celestial/Terrestrial objects with the Azimuth Mirror?

Answer 2

• Point arrow up to take bearing of celestial

* Point arrow down to take bearing of terrestrial

Question 3

What can be Azimuth Mirror be used for?

Answer 3

• Position Fixing.
• Collision Avoidance (Bearing opening = Passing Astern, Bearing Closing = Passing ahead.
• Determining the Compass Error.

Question 4

How may an error occur in the Azimuth Mirror?

Answer 4

If the prism is not horizontal on its axis.

Question 5

What “Correctable Errors” exist on the Sextant, and how are they corrected?

Answer 5

• Perpendicularity
• Side Error
• Index Error

Question 6

What “Non-Correctable Errors” exist on the Sextant?

Answer 6

??

Question 7

What is the advantage of a Magnetic compass over a Gyro compass?

Answer 7

The magnetic compass can determine direction heading from the steering position independent from a power supply.

Question 8

Explain the importance of the Gyro compass?

Answer 8

The gyro compass holds importance because it is relied upon for input by much of the navigational aids located on the bridge.

Question 9

What are the two types of compass cards?

Answer 9

Dry and Wet.

Question 10

What is the liquid inside the bowl of a wet card compass and their ratio?

Answer 10

The liquid inside the wet card compass is a mixture of 2 parts ethyl alcohol to 1 part distilled water.

Question 11

What do the ethyl alcohol and distilled water components of a wet card compass sustain?

Answer 11

•Ethyl alcohol will reduce freezing point in cold conditions.

•Distilled water will reduce evaporation in warm tropical
climates.

Question 12

How would you remove a bubble from a compass?

Answer 12

• Turn the bowl upside down and remove the filling cap
and top it up with pure alcohol. If it is a bowl without a
filling cap inject the alcohol with a syringe.

Question 13

The chief mate tell you the magnetic compass has frozen, what are your actions?

Answer 13

• Obtain the spare bowl from the Nav locker.
• Ensure the correct alcohol to water ratio 2:1 is present.
• Replace the liquid in the frozen bowl with 2:1

Question 14

What maintenance would you carry out every watch as OOW on the magnetic compass?

Answer 14

• Take the compass error.
• Check for bubble in the 
  compass
• Check for free movement of 
  the compass card using a 
  magnet, also known as deflection error.
• Check for any structural changes around the compass.
• Check location of all 
  corrector magnets, given on 
  back o    
  deviation card, DO NOT 
  ADJUST.
• Check for electrical 
  installations not allowed 
  within 1.5m 
  of magnetic compass.
• Report any problems to 
  Master.