The underwater twin of a height contour, tracing one depth value across the seabed. Charts show standard intervals such as 2, 5, 10, 20 and 30 m, drawn from surveyed depths and kept on the safe side: a contour bends seaward around an isolated shoal rather than cutting through it. In ECDIS, contours bound the depth areas and set the safety contour, so their placement drives the ship's alarms.
Push the 10 metre depth contour out around that shoal, it can't run straight through a 9.4.
Also heard as
- isobath
- depth curve
- contour
Related terms
Sounding selection
Choosing which surveyed depths appear on a chart so the shoalest water is always shown.
Shoal-biased
Favouring the shallower value whenever depths are generalised, so a chart never shows more water than exists.
ECDIS
Electronic Chart Display and Information System: the type-approved chart system a ship can carry in place of paper charts.
Nautical chart
A map of waters and coasts made for mariners, showing depths, hazards, aids to navigation and landmarks.