Navigation Instruments Flashcards Preview

(Me) OOW: REVISION > Navigation Instruments > Flashcards

Flashcards in Navigation Instruments Deck (14):

What Navigation Instruments can be used from the Bridge?

•Azimuth Mirror
•Gyro/Magnetic Compass


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

•Point arrow up to take bearing of celestial
•Point arrow down to take bearing of terrestrial


What can be Azimuth Mirror be used for?

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


How may an error occur in the Azimuth Mirror?

If the prism is not horizontal on its axis.


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

•Side Error
•Index Error


What "Non-Correctable Errors" exist on the Sextant?



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

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


Explain the importance of the Gyro compass?

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


What are the two types of compass cards?

Dry and Wet.


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

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


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

•Ethyl alcohol will reduce freezing point in cold conditions.

•Distilled water will reduce evaporation in warm tropical


How would you remove a bubble from a compass?

• 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.


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

• 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


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

• Take the compass error.
• Check for bubble in the
• 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
• Check for electrical
installations not allowed
within 1.5m
of magnetic compass.
• Report any problems to