Safety depth (ECDIS)

Safety depth is the ECDIS setting that marks which charted soundings are dangerous to the ship: any sounding equal to or shallower than the safety depth is shown in bold black rather than gray, so the navigator sees the shoal spots at a glance. It is set to the ship’s draft plus the under-keel clearance the master requires, minus the expected height of tide. Safety depth controls the display of individual soundings; the separate safety contour, derived from it, draws the boundary of safe water and drives the anti-grounding alarms. Setting safety depth too small hides real hazards, so it is part of the pre-passage ECDIS check-off.