Simrad ROBERTSON AP45 manual Heading sensors General Magnetic compass

Page 5-4	Robertson AP45 Autopilot
	Installation

Heading sensors General

Magnetic compass

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

Simrad Robertson AS

Egersund - Norway