Limitations and Recommendations

Note

The International Hydrographic Organization notes that any navigational chart adequately reflects the navigational and hydrographic conditions only at the time the hydrographic survey was conducted.

Due to the high variability of seabed topography in coastal zones, narrow channels, areas of intense river run-off, as well as the influence of wind-driven and tidal phenomena, depths may differ from those indicated on the chart.

Key limitations when operating ECDIS

1. Reduced accuracy near coasts and structures

When navigating in waters near high coastlines or artificial structures, GNSS fix accuracy may be significantly reduced due to deterioration of the geometric dilution of precision (GDOP), caused by the inability to observe some satellites.

Warning

In some cases, a differential correction may degrade the result of the vessel’s position determination.

NSR ECDIS NES-3000 software automatically monitors the quality of the geometric dilution of precision based on GNSS receiver data and generates a warning signal when the limit value of the integral geometric factor is exceeded.

2. GNSS signal degradation

Due to the low signal-to-noise ratio at the GNSS antenna input, cases of signal degradation have been observed while the GNSS receiver continues to output a valid fix flag.

This manifests as:

  • Displacement of the vessel’s position plotted on the ENC

  • Visual drift of the vessel under the influence of current

Tip

SN Circular 255, issued by the IHO, recommends overlaying the radar image on the electronic chart for timely detection of such situations.

3. Recommendations when navigating along leading lines

When navigating along leading lines, it is recommended to always compare the plotted position with the leading lines shown on the electronic chart, which allows timely detection of unstable GNSS performance.

4. Specifics of operation during turning manoeuvres

GNSS receivers have a function for filtering random outliers of navigational parameters over a series of measurements, which improves the quality of coordinate and speed-over-ground vector computation when sailing on a steady course.

Important

During a turning manoeuvre, the vessel’s heading changes significantly faster than the course over ground (COG), which is the direction of the velocity vector produced by the GNSS receiver.

For this reason, the results of automatic ECDIS monitoring of charted hazards during a turning manoeuvre should be treated with caution, since ENC scanning is performed in a strip or sector ahead of the vessel in the direction of the COG, and with a narrow sector part of the water area may remain outside the monitored zone.

Recommendations for monitoring the vessel’s position

In the cases described above, for monitoring the vessel’s position relative to navigational hazards and in fairways, use:

  • Aids to navigation (ATON)

  • Navigational Radar

  • Do not rely solely on ECDIS readings

Important

NSR ECDIS NES-3000 ensures correct operation and display of ENCs in the latitude range from 85°N to 85°S.