Compass Flashcards
What is variation and where can info be found?
Angular difference between T and M North.
Compass rose on chart
Variation chart
GPS
What is Deviation and where can info be found?
Angular difference between M & C North
Ships deviation card
What information must be presented on a deviation card?
Regarding compass swing:
Captain CoC
Corrector’s CoC
Location of swing
Date of swing
Coefficient of data
Cause of deviation:
Permanent magnetism:
Hard iron gets magnetised in correlation to where ship is built
How is permanent magnetism removed?
Athwartship corrector magnets
+
Fore and aft corrector magnets
INDUCED MAGNETISM
Causes?
Removal?
(Bates question)
Caused by materials onboard affecting the compass
Removal: Placement of soft iron spheres and flinders bar
When should the compass be adjusted?
First installation
Become unreliable
Undergoes structural changes or repairs
Electrical or Magnetic equipment is added or removed from ship
Period of 2 years since last adjustment
Explain retention error:
Tendency of ship’s structure to retain some of the INDUCED magnetic effects for short periods of time.
eg. Ship travelling N for for several days may retain some N + S magnetism
Monitoring compass performance:
Frequency?
Logged?
What will the errors indicate?
After large alterations of course
Logged in Compass deviation book
Indicate need for repair, testing or adjustment.
Operational checks of Magnetic compass:
(7)
Gimbal moves freely
Card floating freely
No bubbles
No leaks in liquid
Information on card clear
Azimuth reading devices & illumination in working order
No tools or speakers left in the vicinity
What is a Transmitting Heading device?
Sensor attached to compass to transmit heading information to other ships or shore stations
