Safety contour (ECDIS)

The safety contour is the depth contour the navigator selects in ECDIS to divide safe water from unsafe water for the present draft and required under-keel clearance. The system shades water shallower than the contour and uses it as the trigger for the anti-grounding alarm and for crossing-safety-contour warnings during route check and monitoring. If the chosen value is not held in the ENC, ECDIS defaults to the next deeper available contour, so the displayed contour can be deeper than the operator intended, a known trap.