Compasses Flashcards
How would you check the azimuth bearing circle of the compass was correct?
Take a bearing of terrestrial object with arrow indicating upwards.
Take a second bearing of the same object with arrow pointing downwards.
Both bearings should be the same.
What is the liquid found inside magnetic compass?
One part alcohol
One part distilled water
What is the purpose of both the liquids inside the magnetic compass?
Alcohol – anti freeze purposes
Water – prevents evaporation
Where would you find the ‘lubber line’?
Found inside the magnetic compass bowl, in line with fore and aft line of vsl
Used to reference ships head onto a compass heading.
What checks should be made on the gyro compass?
Datum line at base of repeaters should be aligned with fore and aft axis of vsl, any realignment should be done before the ship sails.
All repeaters should be within 0.5⁰ of the gyro compass
Compass error at least once per watch and recorded in compass error book.
Gyro should be corrected for speed and latitude error while on passage if need be.
What equipment is associated with the Gyro compass?
Gps
Radars
ECDIS
VDR
Autopilot
Rate of turn indicator
When should the magnetic compass be adjusted?
When it is first installed
Becomes unreliable
After any structural repairs or alterations to the ship
If any electrical or magnetic equipment has been fitted near to the compass
If more than 2 years since last adjustment
Who should carry out compass adjustments?
Only done by someone holding a COC as ‘compass adjuster’
If unavailable someone holding class 1 (MASTER UNLIMITED) COC
When should the performance of the magnetic compass be checked?
After carrying cargo with magnetic properties
If any electromagnetic lifting appliances have been used
If the ship has been involved in a collision involving structural damage
If vessel has been laid up for a while
What are the operational checks that should be carried out on the magnetic compass?
Check the gimbal is moving freely
Check the compass card is clear and sharp, should float freely and without any friction
Check the liquid is clear of bubbles with no leaks around the seals.
How do you correct the magnetic compass?
Flinders bar – vertical soft iron corrector, used to correct for vertical soft iron abaft of the compass i.e funnel.
Spheres – quadrantal soft iron corrector – the flinders bar produces small quantity of fore and aft, horizontal and vertical effect on the compass, these spheres correct for these errors.
Heeling error – compensated by permanent magnets set vertically in a bucket beneath the compass.
Horizontal magnets – permanent fore and aft corrector magnets and athwartship corrector magnets.
What is a Flinders bar on a magnetic compass?
vertical soft iron corrector, used to correct for vertical soft iron abaft of the compass i.e funnel.
What are Spheres on a magnetic compass?
quadrantal soft iron corrector – the flinders bar produces small quantity of fore and aft, horizontal and vertical effect on the compass, these spheres correct for these errors.
How is heeling error corrected on a magnetic compass?
compensated by permanent magnets set vertically in a bucket beneath the compass.
What are horizontal magnets for on a magnetic compass
permanent fore and aft corrector magnets and athwartship corrector magnets.
