Since their introduction, Electronic Chart Display and Information Systems (ECDIS) and Electronic Navigational Charts (ENCs) have rapidly become the primary means of navigation aboard many vessels.
As explained in the “ECDIS – Safety Settings,” briefing, ECDIS offers several advantages over traditional paper charts, one of the most important being its ability to alert navigators when a vessel may be approaching dangerous waters. By using safety settings tailored to the vessel’s condition, ECDIS can provide valuable warnings and support safer navigation.
However, these settings must be properly understood, configured and used to ensure they deliver their full benefit.
Safety contour
This is the primary safety feature on the ECDIS. It is set by the user and marks the boundary between safe water and shallow water.
How does it do this?
Before departing port, the ECDIS user must set a value for the safety contour. This should take into account the vessel’s draught and required under-keel clearance. The quality of the ENC data available must also be considered. The safety contour shows on the ENC as an extra wide isoline.
Users should check their SMS for the procedure on setting the safety contour. If it is not set, the ECDIS default value for the safety contour is 30m.
What happens when you get near a safety contour?
When the ECDIS is in monitoring mode (in use on passage), if the vessel’s watch / lookahead vector crosses a set safety contour the user will receive an audible alarm.
The safety contour is the only automatic audible alarm on ECDIS. If the user wishes to have other features – such as wrecks or underwater obstructions – raise an audible alarm, then they must set this themselves when planning the passage as the normal ECDIS default for such objects is only to visually highlight these.
Availability of depth contours
The use of the safety contour can only be accurate if the ENC data within the ECDIS contains enough depth contours. When ENCs were first introduced, most makers used their paper chart series as the source for their data. Unfortunately, this led to some issues, and today many ENCs only contain the standard series of contour lines taken from the old paper chart.
As such, when building the chart display and a contour line is not available, the ECDIS software will draw the next available deeper depth contour in the ENC with a thick bold contour line and shade all areas of the chart between this depth and the zero-metre drying line in a dark blue shallow water colour.
Confidence in the data
When setting a value for the safety contour, not only should the user consider draught and the under-keel clearance requirements but also the accuracy of the ENC hydrographic data. If the ENC in use for a certain leg of the passage shows a low ‘Category Zones of Confidence’ (CATZOC), then this should be accounted for when setting the safety contour.
Sometimes, due to the limited availability of contours in ENC data when navigating near the coast, the vessel will need to navigate inside the safety contour. To improve situational awareness for the user, the latest S-52 standards gives the user the flexibility to turn on the isolated danger symbols to display behind the safety contour in potentially dangerous areas
Safety depth
As described earlier, because of the limited availability of contour lines (commonly to 2m, 5m, 10m, 20m 30m and 50m) this limits the effectiveness of the safety contour, the ECDIS user can set up safety depths independently of the safety contour.
The ECDIS will then display any sounding with a value equal to, or less than, the safety depth value in bold to make them more prominent.
Shallow and deep contours
Before discussing shallow and deep contours, the user must understand depth shades of an ECDIS:
Depth Shades
The user has the option of selecting a simple two-colour shading, or a more in-depth four-colour shading. To enable the use of the four-colour option, the user can set what are called ‘shallow’ and ‘deep-water’ contours in addition to their set safety contour.
Two depth shades
This is the default setting and will only show two depth shades in addition to the inter-tidal area which is exposed at low water:
- Shallow / unsafe waters – Between 0 metres and the safety contour
• Deep / safer waters – Deeper than the safety contour 
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Four depth shades
If the two depth shades option is turned off, the system will switch to displaying four depth shades option using values that are set for the shallow and deep contour:
- User defined shallow contour
• User defined deep contour 
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The use of four depth shades reduces the contrast difference between adjacent depth areas. This may make it more difficult to distinguish between safe and unsafe waters under certain lighting conditions, particularly at night where its use is not recommended.
Shallow contour
The shallow contour value is set by the user and is used to determine all areas shallower than this value. The below first image shows an ECDIS with the shallow contour switched off, and the second with the shallow contour on, illustrating the difference in colours:
Deep contour
This indicates the limit of the sea area where ‘shallow water effects can affect the vessel. It shows the user what the passage plan thinks is deep water. This could be, for example, twice the deepest draft, or 100m in open sea passages. You should consult your SMS for details.
When ‘four shades’ mode is activated, the display will show shallow and deep contour as two additional blue-coloured patterns on the chart panel. While activating the shallow pattern will cross out non-navigable, unsafe water, this can lead to a cluttered screen.
Route check function
When the user has completed planning the intended passage, it is possible to check that the route is safe by using the ECDIS route check function. This checks that the planned route is safe, based on the vessel’s characteristics, and importantly it is free from any charted dangers based on the entered safety settings.
Therefore, the user must ensure that the appropriate safety contour and depth settings are entered before starting this check.
Lookahead function
The ‘lookahead’ or ‘watch’ vector is selected by the user and is expressed either as a distance or a time. Remember that if the watch vector crosses the safety contour it will raise an audible alarm, so it is very important that the user has an appropriate watch vector set at all times.
The setting of the watch vector may need to change throughout the passage. For example, if the vessel is in open water, then a longer / larger watch vector may be more appropriate. However, in confined waters this could mean frequent needless alarms, therefore you may wish to set a shorter / smaller watch vector.
- User defined shallow contour