Charts, standards and display modes
An Electronic Chart Display and Information System presents official vector charts (ENCs, built to the IHO S-57 data and S-52 display standards) with the ship's position and sensor data overlaid. It can be shown at Base, Standard or Full display, each revealing more detail; the OOW must not navigate on Base display alone because it omits many features. ECDIS is distinct from an ECS or a raster-chart (RNC) system, neither of which meets the full carriage requirement on its own. Crucially, the value of ECDIS as an anti-grounding tool depends entirely on how the navigator sets it up.
Setting up for a passage
Configuring ECDIS before departure
- Confirm ENCs covering the whole route are installed and updated to the latest edition.
- Set the safety depth and the safety contour for the vessel's draught plus a margin — this drives the anti-grounding shading and alarms.
- Set guard zones and a check-ahead time so alarms give useful warning, not a wall of noise.
- Plan and check the route, run the automatic route check, and resolve every warning it raises.
- Select an appropriate display and confirm the position, heading and log inputs are valid and sensible.
The safety contour is the heart of the system: set from the vessel's draught, it divides safe from unsafe water and drives the look-ahead and anti-grounding alarms. Source-data quality is shown by the CATZOC rating — a measure of how reliable the survey behind the chart is — and a poorly surveyed area demands extra caution regardless of how confident the display looks.
WARNING — Over-reliance is the real danger ECDIS shows a confident picture even when the survey is coarse or a sensor is wrong. Keep a visual and radar lookout, check the CATZOC, and never let repeated alarms be silenced into meaninglessness — the accident reports are full of ships that motored past their own alarms.
NOTE — A backup is required ECDIS-only navigation needs an approved backup arrangement — a second, independent ECDIS or an appropriate folio of paper charts — so the loss of one unit does not leave the bridge blind.