Simrad Autopilot Compass
18 20220653 / Rev. C
“Another problem that arise as a result of magnetic dip* and
increases with latitude, is what is commonly called the Northerly
turning error in the Northern Hemisphere and Southerly turning
error in the Southern Hemisphere. It is also accentuated by
banking of turns in high speed craft. This phenomenon is true in
all earth seeking magnetic devices.
The effect of the Northerly turning error becomes extremely
critical on higher speed vessels, starting from twelve knots to
approximately thirty knots.
Above thirty knots, it is impractical, if not impossible, to rely
solely on a magnetic seeking device for control of an
automatic pilot.
Because of lateral acceleration in a turn and also because of
the necessary banking of the vessel, part of the dip
component converts to an azimuth component (unless the
compass is gyro stabilized).
The effect of Northerly turning error is generally that the
vessel will steer fairly well on east and west at high speed. It
will over steer on southerly headings but will make wide
swings on northerly headings.
On northerly headings, once the boat has been deflected from
course, it will increase its turn in the same direction rather
than correcting the course in the opposite direction.
The Northerly turning error can be minimized by:
Selecting a compass and autopilot which has been designed
especially with the higher speed boats and Northerly turning
error in consideration.
Keeping boat speed under 15 knots.
Simrad’s solution to this problem is to install our RFC35R Rate
Compass !
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