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Pancyprian Compass & Instruments study materials
Pancyprian Compass & Instruments study resources

Pancyprian Compass & Instruments: Compass Adjustment and Correction

Pancyprian Compass & Instruments · Work through your exam, one topic at a time.

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Compass Adjustment and Correction

Adjustment questions ask which corrector removes which coefficient, in what order, and why a residual always remains. Correctors cancel the field at the compass position; they do not demagnetise the ship.

Correctors on the binnacle

  • Fore-and-aft magnets correct coefficient B, whose deviation is greatest on east and west headings.
  • Athwartship magnets correct coefficient C, greatest on north and south headings.
  • Soft-iron spheres correct quadrantal deviation D, greatest on intercardinal headings.
  • The Flinders bar corrects the effect of vertical induced magnetism in the ship's soft iron, which changes with magnetic latitude.
  • The heeling magnet in its vertical tube corrects heeling error, adjusted on north and south headings in calm water.
  • Coefficient A, constant on all headings, is dealt with by checking card and lubber line alignment.

Swinging ship

  1. Prepare: calm water, normal degaussing state, no magnetic cargo or loose ironwork near the binnacle, gyro or azimuth available for true bearings.
  2. On cardinal headings reduce B and C.
  3. On intercardinal headings reduce D with the spheres.
  4. Set the Flinders bar for the magnetic latitude, adjusting on passage as needed.
  5. Re-swing, record residual deviation and issue the deviation card.

Worked example

Deviations east positive: N +3, S -1, E +2, W -4. C = (N - S)/2 = (3 - (-1))/2 = 2.0 degrees E. B = (E - W)/2 = (2 - (-4))/2 = 3.0 degrees E. On north or south, adjust the athwartship corrector to remove the 2 degrees C; on east or west, adjust the fore-and-aft corrector to remove the 3 degrees B. A = (N + S)/2 = 1.0 degree remains constant and cannot be removed with magnets, so check alignment and pivot.

Traps

  • Adjusting B on north or south, or C on east or west, instead of where each is greatest.
  • Expecting correctors to eliminate deviation; a residual always stays and must be tabulated.
  • Adjusting while a magnetic item, degaussing cable or steel tool is altering the field.
  • Confusing the Flinders bar with the quadrantal spheres.