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safety depth Safety depth is an easy concept in ECDIS and ECS. It is a user assigned depth that will turn the displayed soundings from gray in deeper waters to black in equal to or shallower waters. Test this with any program to see how it works. It does not depend on other settings and this choice has no other effect on the display. The mariner's job is to decide what this value will be for their vessel. Generally it would be your draft plus the largest negative tide you might expect, plus some safety factor. Larger vessels might also have to account for effects of loading and potential effects of squat Areas of grey soundings would then be generally safe, whereas black sounding are shallower than what you have decided you need. When needs arise to transit these areas, you may have to look into the tides in more detail. See also safety contour

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