Page 8 - Electronic Navigation Cyber Book

1.3.1 Static errors

An alignment error can be:
• an error existing between the indicated heading and the vessel's lubber
line
• an error existing between the indicated lubber line and the fore and aft
line of the vessel.
Both of these errors can be accurately eliminated by critically aligning the
compass with the ship's lubber line at installation.

Transmission error
An error existing between the indicated heading on the master compass
and the heading produced by any remote repeater is a transmission error.
Transmission errors are kept to a minimum by the use of multispeed
pulse transmission.

Variable errors
Variable compass errors can effectively be classified into two groups.
• Dynamic errors that are caused by the angular motion of the vessel
during heavy weather and maneuvering.
• Speed/latitude errors that are caused by movement of the vessel across
the earth's surface. The magnitude of each error can be reduced to some
extent as shown in the following text.

1.3.2 Dynamic errors
Rolling Error
The gyrocompass is made to settle on the meridian under the influence
of weights. Thus it will also be caused to shift due to other forces acting
upon those weights. When a vessel rolls, the compass is swung like a
pendulum causing a twisting motion that tends to move the plane of the
sensitive element towards the plane of the swing. For a simple
explanation of the error consider the surge of mercury caused in both the
north and south reservoirs by a vessel rolling. If the ship is steaming due
north or south, no redistribution of mercury occurs due to roll and there
will be no error.

But with a ship steaming due east or west, maximum lateral acceleration
occurs in the north/south direction causing precession of the compass.
However, rolls to port and starboard are equal, producing equivalent
© 2018 Digital Galaxy Index 8