Instruction Manual
20220653 / Rev. C 7
The sensor coil is either mechanically gimballed or has a floating
ring core (RFC35). This will prevent an uneven distribution of
the magnetic field in the sensor coil when the boat is rolling and
pitching. Compared to a magnetic compass, however, the
fluxgate compass is more sensitive to the motions of a vessel. In
rough sea conditions or in sharp turns at high speeds, the sensor
may be temporarily displaced from the horizontal plane. A
distorted and unstable heading input to the autopilot is the
resulting effect. A lot of attention has been paid to reduce this
effect when designing the RFC35 Fluxgate compass and it has
proven to be successful. The optimum performance is
accomplished with the Rate Compass which is a rate sensor
stabilized fluxgate compass.
Except from the Rate Compass, fluxgate compasses are not
recommended as autopilot compass on steel boats, mainly due to
lack of efficient “heeling error” compensation. This
compensation is needed when a magnetic heading sensor is
mounted on top of the wheelhouse or in the mast.
2.3 Rate compass (RC25, RC36, RC37)
The Simrad Rate Compass is in principle a combination of a
solid state rate sensor and a fluxgate sensor, where the rate
sensor is slaved to the fluxgate sensor.
The rate sensor will momentarily pick up any angular changes in
azimuth, but is almost unaffected by roll and pitch.
As the “rate heading” will drift, the fluxgate sensor is needed to
maintain the (magnetic) heading. However, as the rate sensor is
the primary “heading” source, the fluxgate signal can be more
dampened and thus it will not contribute to the instability caused
by heavy rolling and pitching.
The Rate compass gives a more stable and precise autopilot
steering on any type of boat. It also eliminates the effect of the
distorted horizontal magnetic field at high latitudes and the well
known s-ing phenomena when on autopilot steering.
It can also be used as “stand alone” compass to provide a stable
heading input to a compass repeater, radar or other equipment.
However, care should be taken when using it on bigger steel
boats that can have a strong local disturbing magnetic field that
makes a good calibration of the fluxgate impossible.
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