Sunday, March 2, 2008



Adjustments at sea. These adjustments are made with the ship on an even keel and after steadying on each heading. When using the gyro, swing from heading to heading slowly and check gyro error by sun's azimuth or ranges on each heading if desired to ensure a greater degree of accuracy. Be sure gyro is set for the mean speed and latitude of the vessel. "OSCAR QUEBEC" international code signal should be flown to indicate such work is in progress.

1. Adjust the heeling magnet, while the ship is rolling, on north and south magnetic heading until the oscillations of the compass card have been reduced to an average minimum. (This step is not required if prior adjustment has been made using a dip needle to indicate proper placement of the heeling magnet.)
2. Come to an east (090°) cardinal magnetic heading. Insert fore-and-aft B magnets, or move the existing B magnets, in such a manner as to remove all deviation.
3. Come to a south (180°) magnetic heading. Insert athwartship C magnets, or move the existing C magnets, in such a manner as to remove all deviation.
4. Come to a west (270°) magnetic heading. Correct half of any observed deviation by moving the B magnets.
5. Come to a north (000°) magnetic heading. Correct half of any observed deviation by moving the C magnets. (The cardinal heading adjustments should now be complete.)
6. Come to any intercardinal magnetic heading, northeast (045°). Correct any observed deviation by moving the spheres in or out.
7. Come to the next intercardinal magnetic heading, southeast (135°). Correct half of any observed deviation by moving the spheres. (The intercardinal heading adjustments should now be complete, although more accurate results might be obtained by correcting the D error determined from the deviations on all four intercardinal heading.
8. Secure all correctors before swinging for residual deviations.
9. Swing for residual undegaussed deviations on as many headings as desired, although the eight cardinal and intercardinal headings should be sufficient.
10. Should there still be any large deviations, analyze the deviation curve to determine the necessary corrections and repeat as necessary steps 1 through 9 above.
11. Record deviations and the details of corrector positions.
12. Swing for residual degaussed deviations with the degaussing circuits properly energized.
The above check-off list describes a simplified method of adjusting compasses, designed to serve as a simple workable outline for the novice who chooses to follow a step-by-step procedure. The "Dockside Tests and Adjustments" are essential as a foundation for the "Adjustments at Sea", and if neglected may lead to spurious results or needless repetition of the procedure at sea. Hence, it is strongly recommended that careful considerations be given these dockside checks prior to making the final adjustment so as to allow time to repair or replace faulty compasses, anneal or replace magnetized spheres or Flinders bar, realign binnacle, move gyro repeater if it is affecting the compass, or to make any other necessary preliminary repairs. It is also stressed that expeditious compass adjustment is dependent upon the application of the various correctors in a logical sequence so as to achieve the final adjustment with a minimum number of steps. This sequence is incorporated in the above check-off list and better results will be obtained if it is adhered to closely. Frequent, careful observations should be made to determine the constancy of deviations and results should be systematically recorded. Significant changes in deviation will indicate the need for readjustment.
To avoid Gaussin error when adjusting and swinging ship for residuals, the ship should be steady on the desired heading for at least 2 minutes prior to observing the deviation.

Definition of Gaussin error: Deviation of a magnetic compass due to transient magnetism which remains in a vessel's structure for short periods after the inducing force has been removed. This error usually appears after a vessel has been on the same heading for a considerable time.