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Vessel icon / heading vector appears to be incorrectly oriented - Chuck - Raymarine - Moderator - 09-16-16 09:39 AM
Vessel icon / heading vector appears to be incorrectly oriented
Two of the most commonly confused navigational terms are heading and course over ground (COG). Heading is the angular designation of the orientation of the vessel with respect to true or magnetic north ... in short, it is the direction in which the vessel is pointed. COG is the angular designation give to the direction in which the vessel is moving over the earth with respect to magnetic to true north. As indicated within this definition of COG, the vessel must be in motion to express the direction of its movement. Depending upon the vessel's speed and leeway (resultant of current and wind vectors), heading and COG may be very close or very different in value. Generally speaking, heading and COG will be closer in value as the speed of the vessel increases, thereby reducing the effects of leeway. Correspondingly, slower moving vessels will be more affected by leeway and as such slower moving vessels will typically display greater differences in the values reported for heading and COG.
One may determine whether the Raymarine system has been interfaced to a source of heading data by configuring the MFD to display the "Heading" data item within the MFD's Databar, a Databox, or within one of the Data application's Data Panels. Should the reported value of "Heading" data item be ---, then one may assume that the Raymarine system has not been interfaced to a source of heading data.
Once underway and making good way, the Chart application of MFDs operating within a system lacking a source of heading data will:
- orient the chart according to the Chart Orientation configuration setting
- offset the chart and vessel icon according to the Boat Position configuration setting
Head-Up vs Course-UP Chart orientation ... Like the confusion over Heading and COG, many operators of systems lacking a Heading data source erroneously assume that the Chart application should be configured to Course-Up orientation rather than Head-Up orientation when seeking to have the system orient the chart in the direction in which the vessel is moving. Head-Up chart orientation is most commonly used by those operating in pilotage waters and/or to have all items displayed within the Chart application to be displayed relative to the vessel's head. In contrast Course-Up is associated with the the Chart application's navigation features (i.e. Go To Cursor/Waypoint and Follow Route). Should the system be commanded into navigation mode through execution of one of the aforementioned commands and should the Chart application then be commanded into Course-Up, then the displayed chart will be oriented to match that of the navigational course line to the waypoint/cursor position, which may or may not be the direction in which the vessel is moving over ground (COG) or pointed (heading).
It is not necessary to interface a heading data source to the system unless it is desired to have the vessel icon be properly oriented when the vessel is stationary or operating at maneuvering speeds or should one desire to utilize one of the system's heading dependent or heading enhanced features. Raymarine recommends that accurate 10Hz or greater heading data be supplied to any system using using any of (but not limited to) the following Radar and Chart application features:
- MARPA
- AIS Targets Displayed within the Radar Application
- Waypoints Displayed within the Radar Application
- North Up or Course Up orientation within the Radar Application
- Radar Overlay within the Chart Application .. may be used with COG alone.
- Heading Vector within the Chart Application
- Vessel Icon Orientation within the Chart Application (will default to COG when no heading data source is detected)
- Heading Databar and Data application data items
- Other heading dependent features.
Should the MFD be interfaced to a source of heading data and the vessel icon incorrectly oriented and/or appear to be crabbing as the vessel is making way, then the system's heading data source would be deemed to be in need of calibration and alignment or need to be serviced/replaced. Should heading errors be detected, then the vessel's heading data source will need to be re-calibrated for deviation and then aligned to the correct heading. The owner's manual for the heading data source should be consulted for information concerning how to calibrate it for deviation and then align the compass. After doing so, then the heading should be tested against vessel's properly calibrated fluid filled compass (if so equipped) again. Should heading error continue to be detected then it is recommended that the heading data sensing device be serviced/replaced.
Before performing any calibration and alignment of a heading sensor, it is strongly recommended that the area around the heading sensor be inspected to ensure that all sources of magnetism (ex. ferrous materials, electric motors, high current carrying conductor have not been located within at least 3' of the heading sensor. Please click here to view a FAQ addressing this subject. The most common source of heading data onboard a vessel is an autopilot system. Other heading sources include the retired ST60+ Instrument Compass, Pathfinder Smart Heading System, and third party NMEA 0183 and NMEA 2000 GPS Compasses and magnetic heading sensors.
RAYFAQ#