Simrad ROBERTSON AP45 - Manual (Page 54)

Page 5-4 Robertson AP45 Autopilot
Installation
Simrad Robertson AS
Egersund - Norway
AP45 is designed for connection to one compass only. However, a combination of
two compasses are possible as CD109 and Fluxgate/Gyro has separate input pins
in the J2 Compass connector. This means you can combine a magnetic compass
with either a fluxgate- or a gyrocompass.
The type of heading sensor used in the standard scope of supply may vary from
distributor to distributor as a result of practical experience and the preferences of
their market place.
The CD109 Course Detector is fitted to the vessel's existing magnetic compass or
to one particularly installed for the autopilot (“Magnetic compass”, page 5-4.).
The Robertson RFC35NS Fluxgate Compass can be connected directly to the
control unit (“RFC35NS Fluxgate Compass”, page 5-6), whilst other makes of
fluxgate compasses require a FI100-40 Fluxgate Interface (“FI100-40 Fluxgate
Interface”, page 5-8).
If a gyrocompass is used as heading sensor, the G40A or G45 Gyro Interface is
required (page 5-9).
To obtain an accurate heading from the magnetic compass, great care should be
taken when determining the location of the compass.
Select a location that provides a solid horizontal mounting base, free from
vibration and as close to the vessel's centre of roll and pitch as possible. It should
be as far as possible from disturbing magnetic interference such as the engines,
cables, transmitter antennas or other electro magnetic objects.
Note! The compass must be compensated.
Heeling error
Heeling error may be observed when the boat is rolling and pitching, causing an
unstable compass card. This can be adjusted for by using a "heeling magnet"
placed vertically below or above the exact centre of the compass. The magnet is
normally placed with the red end up in the Northern hemisphere and the blue end
up in the Southern hemisphere. The correct distance between magnet and
compass can best be found during sea trials. The heeling error can also be reduced
by mounting the compass close to the vessel's centre of roll and pitch.
Northerly/southerly turning error
Symptoms of northerly turning error are that the vessel is "S-ing" on northerly
headings when at high latitudes. The reason for this phenomena is that the earth's
magnetic fluxlines are parallel to the earth's surface only at the equator, and thus
no vertical magnetic component exists. When moving further north from the
equator, the vertical component of the earth's magnetic field increases.
The directional reading from a magnetic compass is based upon the horizontal
component of the earth's magnetic field. This component becomes smaller and
smaller with increasing latitude, while the vertical magnetic component increases.
The resulting effect at high latitudes is that magnetic compasses become sluggish
and appear to be unstable. These symptoms become more apparent as speed
increases.
The same phenomena is experienced in the southern hemisphere, but on southerly
headings and is referred to as southerly turning error.
There is no patent cure for this problem, besides making a proper installation and
compensation of the compass.
CD109 Course Detector mounting
Heading sensors
General
Magnetic compass