Correction Method Of Ship Magnetic Compass Self Deviation

Step 1: measure the compass deviation of the East, West, South and north main points. The method can be obtained by comparing the course of electric compass with that of magnetic compass. 

If the error of gyrocompass is very small, the course of gyrocompass can be regarded as true course, magnetic course = true course - magnetic difference (magnetic difference is positive in the East and negative in the west, marked on the azimuth circle of chart), self deviation = magnetic course - gyrocompass course (i.e. ship course actually displayed by magnetic compass).

Step 2: after calculating the self deviation of the four main points of East, West, South and North, compare the group of East-West self deviation with the group of North-South self deviation. 

If the self deviation of the East-West self deviation is greater than that of the West self deviation, then in this group, as long as the longitudinal magnetic rod is adjusted (moving the magnetic rod up or down) or B is rotated (clockwise or counterclockwise) when the ship is sailing East In the same way, for the North-South course with large deviation, adjust the transverse magnetic bar or C fine adjustment on the course with large deviation.

Step 3: before correction, record the number of the magnetic rod or the scale position of the B and C knobs and the red end orientation of the magnetic rod (for recovery), adjust the transverse magnetic rod or C knobs by the North-South course deviation, that is, when the ship is heading south or North (that is, when the compass is heading between 355 ° and 005 ° the ship can be taken as the North Course), and adjust the transverse magnetic rod (if it is a knob, turn it) Turn C to fine-tuning button), and observe the change of compass degree at the same time. Generally, it is appropriate to eliminate the deviation to ± 1.5 degrees. If the deviation is eliminated to very small or zero, the heading deviation will be too large on the contrary;

In the same way, adjust the left and right longitudinal magnetic bars or B knob for the East-West course deviation. (for example: if the self deviation of four main points measured by a certain ship is n + 3.5 °, s-1.5 °, E-4 ° and W + 3.5 ° respectively, the ship is just going north, the course of the gyrocompass is 3 ° and the magnetic difference in the sea area is 4 ° w (i.e. - 4 °), it can be seen that the magnetic course should be 7 ° but the magnetic compass shows 3.5 ° (the course of the gyrocompass). 

At this time, the transverse magnetic bar can be adjusted to increase the magnetic compass to 5.5 ° or 6 ° and retain + 1 to 1.5 ° self deviation In the same way, if the ship is sailing 90 ° to the East, the magnetic heading should be 94 ° but the magnetic compass display is 98 °, adjust the longitudinal magnetic bar to reduce the magnetic compass to 95.5 ° or so, and then observe the self deviation value of 8 directions. If it is less than ± 3 °, OK, if it is more than ± 3 °, adjust again according to the above method). If the self deviation after adjustment is greater than the original, please restore and contact the company In charge or contact the compass master directly.