Use of the Safety Depth and the Safety Contour in ECDIS
Safety Depth: Value set by the mariner that is used by ECDIS to portray soundings as black if they are equal to or shoaler than the value and gray if they are deeper.
Safety Contour Depth: Value set by the mariner that is used by ECDIS to select a “Safety Contour” from among the depth contours available in the SENC that is equal to or deeper than the value.
Safety Contour: A specific depth contour set by ECDIS. It demarks the boundary between “safe-water” and shallow water with an extra wide isoline and is used to give an alarm if the ship, within a time specified by the mariner, is going to cross the safety contour. It is also used to determine the tints used for depth areas and for other purposes.
The following assumptions were made in creating the scenarios described in these slides.
1.ECDIS allows the mariner to set the Safety Depth and the Safety Contour Depth independently.
2.The mariner sets the Safety Contour Depth equal to the “Vessel Safety Draft,” which is calculated as: Vessel Safety Draft = Vessel Draft + Dynamic Squat + Safety Margin
3.Depths are considered “safe” if they are equal to or deeper than the Safety Contour Depth.
4.Depths shoaler than the Safety Contour Depth are considered “unsafe.”
3 Ways to Set Safety Depth and Safety Contour Depth
• IMO Performance Specifications and S-52 provide flexibility in how the safety depth and safety contour depth may be set by the mariner.
• The affect on the portrayal of soundings and contours from the use of each of these three options are described in the following below pictures.
1. Safety Depth equals Safety Contour Depth
2. Safety Depth is shoaler than Safety Contour Depth
3. Safety Depth is deeper than Safety Contour Depth