General Compass Questions Flashcards
Why do you have a Magnetic Compass?
SOLAS Ch5. Requires all ships irregardless of size shall be fitted with a properly adjusted standard magnetic compass. Independent of any power supply, to determine the ships heading & display this reading at the main steering position.
- A Pelorus or brg device to take bearings over an arc of the horizon of 360’
- Means of correcting heading and brg to true at all times. (Deviation Card)
- Spare compass ships over 150GT
What SI covers Magnetic Compass?
SI 280 of 1985 (Nav Equipment)
Who can adjust a compass on a Irish Reg vsl?
Adjustments should be made by a compass adjuster. But if unavailable - Master may carry out. (Class 1 ticket + Expertise in compass adjusting)
When would you check / adjust your compass?
First installed
Major repairs after collision fire or grounding
After a long layup
Correctors have been tampered with
After period of 2 yrs with no record of Deviations
When would you carry out a tentative adjustment?
Change of operating regions (S.Pac - N.Eur)
Within 50nm of Equator.
After adjusting Heeling Error bucket on voyage.
How would you prep for swing?
Hold a meeting:
C/E: Get Funnel to Sea Going Temp.
C/O: Ship upright and Minimal Trim
Bosun: Stow on deck and SFS
2/O: Plan passage to Swinging ground,
clear of magnetic anomalies, and 3 cables from other ships, good transits
3/O: Inform Port. Put secrete message out to other ships. Hoist OQ signal flag.
Concerns when using Gyro to swing by?
Gyro error must be known
Variation must be known
Latitude and Speed corrections.
New Electrical equipment on the bridge? How close?
Should be marked on the equipment. If unknown, not within 7m.
1)What is Retained Magnetism? 2)How is it caused? 3)How is it solved?
1) When a soft iron develops hard iron properties.
2) When a ship is steering the same course for a prolonged period of time.
Or when a ship has been laid up for a prolonged period of time.
3)Solved by Rolling on Deck or Annealing.
What is Gaussian Error?
Effect on the compass of Electrical Eddy Currents.
Caused as the vessel swings through the earths magnetic field.
Eliminated by allowing the vessel to steady on desired heading for 2 mins (steady on Cardinal / Inter Cardinal) Full Swing should take approx 40 mins)
What is Retentive Error?
When a ship steers the same course for a prolonged period of time.
What does a VFI do?
Vertical Force Instrument measures Dip. The angle of H.
What should be your concerns with the compass when changing Latitudes and how will you correct for it?
The effect on the compass of the Heeling bucket. When heading from High Lat to lower Latitudes.
Lower the heeling error bucket. Continue to Lower the further south you go once you cant go any lower - remove any magnets when cant lower any further and then flip the final magnet.
How would you check the Soft Iron Correctors for retained magnetism?
Rotate the spheres Horizontally and Vertically. Check for deflection of more than 2 degrees.
Turn Flinders bar upside down and check for change on compass card 2 degrees.
What can be done to the compass when changing hemispheres?
Split B!!!
Stop at the equator and place the vessel on an E/W heading, take out the flinders bar and remove any deviation present with Permanent magnets. When back in higher latitudes place vessel again on E/W heading whatever deviation present is caused by induced B. The funnel - correct with Flinders.
