Simrad GC80/GC85 Dual Gyro Compass
22 20221537 / D
Speed error correction
All gyro compasses will generate a heading error caused by the
vessel speed and earth rotation. GC80/GC85 calculates this error
based on latitude and speed input information, and corrects
automatically the bearing signal output. If no speed information
is available, the gyro compass will output a heading error either
westwards or eastwards depending on the vessel’s course.
If speed information is unavailable, the figure on next page may
be used for manually calculating the heading error.
In this figure, the following values are used as example:
- Latitude: 40°
- Vessel speed: 16 knots
- Vessel heading: 30°
The heading error is found by:
1 Drawing a line between the latitude and the vessel heading
(shown with gray line on the figure)
2 Drawing a straight line (broken line in the figure) between
the vessel speed and the point where the latitude/heading
line intersects with the solid black line in the figure.
In the example above, the figure shows a speed error of appr.
1.1°, and the true bearing should then be 30°-1.1° = 28.9°.
Note! When the course is within 270° - 0° - 90°, true heading is found
by subtracting the speed error from the compass heading.
If the course is within 90° - 180° - 270°, true heading is found
by adding the speed error to compass heading.
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