3.8.11 Voyage execution and monitoring

ECDIS is equipped with a series of functions to assist the mariner in conducting the planned voyage.

1. Chart Scale

On approach to port, the largest scale chart should be in use. Original chart scale (1:1) indicate all navigational dangers. Navigational dangers such as cables, pipes, buoys, oil platforms, etc. may disappear from the display when the chart is zoomed in/out.

Auto-filter or ‘SCAMIN’ may remove information from the display if the best scale chart is not being used. Operators must know how to select the best scale chart to avoid the auto-filter feature removing information when using ENCs.

2. Radar Overlay

If this function is available it can provide the navigator with a quick confirmation of the reliability of the GPS position. If the radar echo is not aligned with the charted coastline it is likely that the position input is in error.

3. Parallel Indexing

Parallel index must be noted on the ECDIS (user chart facility) the same way as they would be noted on the chart. This allows parallel index information (distance and object) in order to set it on the radar.

4. Position Fixing

Good seamanship dictates that positions obtained from GPS are to be cross-checked during the watch and will depend upon the proximity of distinguishable landmarks. GPS position-fixes should also be regularly cross-checked using independent methods when available including:

• Parallel indexing and use of clearing bearings;

• Radar cross bearings or ranges;

• Visual cross bearings.

It is essential that at any one time the Officer of the Watch knows exactly where the vessel is in relation to the intended passage plan.

On ocean passages the position may be manually plotted intermittently but on coastal or pilotage passages the frequency of manual plotting must be increased. The following table outlines the minimum position fixing interval:

Area	Frequency	Fix Type
Ocean Passages/ Deep Sea	Every 2 hours When possible	Alternate Global Navigation Satellite System Astronomical observations
Coastal Waters	Every 30 minutes, increasing frequency to every 20 minutes approaching restricted waters.	Visual bearings Radar range/bearings Electronic aid
Restricted Waters	Every 20 minutes, increasing frequency to every 6 minutes in extremely confined waters and port arrival/departure.	Visual bearings Radar range/bearings Electronic aid

The electronically plotted positions should remain on the chart until the completion of the voyage.

5. Track History

The ECDIS should be set to display the vessels track history. This will give a quick indication of the effects of set.

6. Dead Reckoning

This facility can be used as an easy check to ensure gyro heading and log speed broadly confirm the actual COG input from the GPS.