Permanent magnetism and Induced magnetism, correction

Permanent magnetism and Induced magnetism, correction

Parmanent Magnetism:
PQR force is due to parmanent magnetism.
Caused during ship building.
Remain constant throughout lifespan.
Do not change with latitude, heading, northern or southern hemisphere.
Correction is done by parmanent magnets.

Correction of parmanent magnetism:
F & A and Athwartship magnets.
Parmanent magnet of 8” in length and diameter of 3/8” and 3/16”.
To correct “Permanent B” and “permanent C” coefficients.
For Permanent B, placed in F&A direction.
For Permanent C, placed in Athwartship direction.

Induced Magnetism:
Caused for a small period of time.
Do not remain constant.
Change with latitude, heading, northern or southern hemisphere.
Correction is done by soft iron. (Flinders bar, quadrantal spheres)

Correction of Induced magnetism:
If -Bi, place flinder bar forward.
If +Bi, place flinder bar aft.
If superstructure abaft the compass, flinders bar on forward part. If superstructure forward of the compass, flinders bar on after part.
If +D, place quadrantal spheres athwartship.
If -D, place quadrantal spheres F&A.