Electronic Chart Display and Information System combines official ENCs with the ship's position, heading and speed and checks the planned and actual track against hazards. The bridge team sets a safety contour and safety depth, and the system alarms when the route crosses shallower water. Because its warnings come straight from chart data, poor or stale survey data feeds directly into what the bridge trusts.
Pilot says ECDIS keeps alarming at the turn, the safety contour snaps to the 10 metre line there.
If the chosen safety contour does not exist in the ENC, ECDIS uses the next deeper contour available, so sparse contours can push the alarm line well offshore.
Related terms
ENC
Electronic navigational chart: an official vector chart database used in ECDIS, built from objects with attributes.
S-57
The international data transfer standard behind most electronic navigational charts, built on objects and attributes.
Depth contour
A chart line that follows a single depth below chart datum across the seabed.
S-100
The international data framework behind a family of marine products, including vector charts, gridded bathymetry and water levels.