Safety Depth, Contours and Display Configuration

A vector-chart display is a filtered view of a database. Safety depth, safety contour, shallow contour, deep contour, category layers, and scale determine which dangers are emphasised. Small-craft plotters do not all use ECDIS terminology or behaviour, so the skipper must learn the fitted system rather than assume that a familiar colour means the same thing on every unit.

Choose settings from the passage, not from a factory default. The safety calculation should consider draught, required under-keel clearance, expected squat where relevant, predicted height of tide, and uncertainty in tide, sea state, pressure, survey quality, and position. Entering the vessel's draught alone is not a complete safety-depth decision. Record the operational limit used, and check how the display rounds to an available contour.

Test the result at the scales that will actually be used. Zooming out can suppress isolated dangers, soundings, text, and detail; an overscale or underscale warning needs a response, not dismissal. Check the route leg between waypoints, not just each waypoint, and inspect the turn geometry and cross-track corridor. The autopilot will follow the supplied geometry faithfully even when the route is unsafe.

Treat alarms as barriers with owners and actions. A depth alarm that sounds only after the planned margin has gone is too late; an alarm that sounds continuously will be silenced. Brief what each alarm means, who acknowledges it, what immediate action follows, and when the passage is paused. Recheck configuration after software updates, vessel loading changes, charter handovers, and profile changes.