Magnetic Compass

Question 1

What is the advantage of magnetic compass?

Answer 1

Independent

Question 2

Explain Gaussin Error

Answer 2

When VL alters course the EMF cuts through the vessel at different rates causing eddy currents, and a temp deviation. When ship alters to stbd (from N heading) dev is deflect to west (left).

While the swing is constant, the effect of gaussin error is similar to that of coefficent A.

The error will die off as the new course settles.

When adjusting the compass it is important to let the vessel settle on the course to ensure that the correction is not distorted by gaussin error.

Question 3

When would you book a compass adjuster as Master?

Answer 3

• period of 2 years since last adjustment and record of compass deviations as not been maintained.
• present deviation is more than +/- 5 deg from average deviation.
• structural changes or struck by lightening.

Question 4

What does the Master do in the absence of a compass adjuster?

Answer 4

Tentative Swing if the compass is unreliable. Temp adjustment until an adjuster is available.

Question 5

What would you do as Master when joining a new vessel, after a period of lay-up, with regards to the compass?

Answer 5

• call compass adjuster
• if not available, a class 1 coc can make adjustments BUT THEY SHALL DO THESE FIRST!:
• Check for bubble error, deflection error, gimble moving, location of all magnets as per deviation card, any structure changes or new electrical installations (1.5m).
• Check retentive error in flinders bar, KBs - remove it by rolling or annealling.
• check deviations again
• if still fucked Master must complete a tentative swing.

-

Question 6

How do you prepare for a tentative swing?

Answer 6

Call for meeting.

• 2/O (Passage plan, select clear area with lots of transits searoom and less traffic)
• 3/O (in charge of dev calc hoist OQ, GMDSS securite message, inform VTS if in area ~(ask permission)

ChOff (ensure ship is upright, less trim, take the con, ensure crew have enough Hrs of rest)

• Bsn (secure the ship).

Question 7

What coefficients are you correcting during tentative swing?

Answer 7

B, C and D.

B - P&’c’ (hard iron fore and aft & vertical soft behind the compass flinders bar (split B remember but cannot correct for ‘c’)

C - Q&’f’ (hard iron athwartship and vertical soft beside funnel)

Question 8

Explain how you will correct the compass as Master.

Answer 8

Start with Coefficient B

East or West heading first (max deviation on east and west (sine curve). Slow steaming. Transit brg prep and take brg from magnetic compass. Verify the deviation as we already know the variation (compass error). Alter fore & aft hard iron up and down to adjust verify dev 0.

Then turn North and start coefficent C

Again use transit and adjust the athwartship hard iron correctors.

Then turn NE and start coefficient D

Again use transit and adjust KBs out and in to make deviation 0.

FIRST HALF DONE.

Now turn west and correct coefficient B but ONLY CORRECT FOR HALF DEVIATION.

Turn south and correct for coefficient C BY ONLY HALF.

Turn South East and correct coefficient D KBs by HALF ONLY.

Then create deviation card and complete a full swing - book compass swing ASAP. Continue with compass errors every watch.