Module 7 - Charts & Publications
Electronic Charts (ENC) and ECDIS Awareness
What you will learn
Distinguish chart data from the system that displays it, configure and interrogate the presentation, recognise common-source failures and prepare a usable backup before relying on electronic navigation.
A crisp moving map is a chain of chart data, software, settings, sensors, power and human interpretation. Zoom, alarms and a second screen do not create more surveyed detail or independent evidence.
A Raster Navigational Chart represents the appearance of a paper chart in a geo-referenced raster image. It can be panned and visually enlarged, but enlargement cannot create new source detail or turn individual marks into queryable chart objects. An Electronic Navigational Chart stores vector chart objects and attributes that compatible software can select, query and portray. That flexibility creates responsibility: layers, scale, safety settings and palette can hide or emphasise information without changing the underlying survey.
ECDIS means Electronic Chart Display and Information System. It is a regulated shipboard system whose compliance depends on the approved system, suitable official data, updates, configuration, trained use and backup arrangements—not on the presence of a moving chart alone. A leisure chartplotter or Electronic Chart System may use valuable chart data, but it does not become ECDIS because its screen resembles one or because it can display an ENC-derived product.
Electronic warnings depend on correct inputs and settings. A safety contour, look-ahead alarm or route check cannot compensate for wrong draught, tide assumptions, datum, antenna offset, disabled layers, unsuitable compilation scale or an uncharted danger. Zooming beyond the intended data scale can produce a clear overscale picture without additional verified detail. Restore a suitable scale and inspect source, quality and portrayal information before deciding the route is clear.
Connected equipment can share failure modes. Two displays may repeat one GNSS antenna, datum setting, heading input, route file, chart licence or power supply. Challenge the chain with evidence that can fail differently: identified visual or radar information when available, depth trend with tide and sounder reference understood, and a current backup method that the crew can actually use. MCA guidance specifically warns against over-reliance on a single electronic aid and requires regular cross-checking.
Worked example
A yacht's primary plotter and tablet differ only in their screens: both receive one GNSS position and one route file from the same gateway.
- 1List the common dependencies: antenna, receiver, datum, antenna offset, route data, gateway, chart source and likely vessel power.
- 2Treat agreement between the screens as confirmation that the data was repeated, not confirmation that the position or route is correct.
- 3Choose a cross-check with different failure modes, such as identified radar ranges, visual bearings or depth trend interpreted against current chart and tide.
- 4Prepare a current backup that remains available after the credible common failures and make sure the watch can use it.
Sense check: Adding screens increases independence only when the sources, power, data and failure paths are genuinely separate enough to challenge one another.
| Layer of the chain | Question to ask | Failure that can look normal |
|---|---|---|
| Chart data | Official or leisure product; coverage, edition/update and compilation scale? | Old or unsuitable data still renders cleanly |
| Portrayal | Scale, layers, category, palette and safety settings? | A feature is filtered, decluttered or shown differently |
| Position and heading | Which antenna, datum, offset and sensor feed? | Every connected display repeats one displaced source |
| Alarm logic | Correct draught, contour, route geometry and look-ahead? | No alarm because the input or setting is wrong |
| Power and network | What fails together and how is the backup isolated? | Nominally separate screens share one supply or gateway |
| Human use | Can the watch interrogate, cross-check and recover? | A capable system is misunderstood under pressure |
Challenge a clear-looking electronic corridor
At night the plotter shows a clean route through a narrow approach. It is heavily zoomed in; several soundings disappeared after a palette change, and the tablet repeats the boat position from the same wireless GNSS feed.
1. Identify the chain
Confirm chart provider and product, data and licence status, current update, display type, sensor inputs, datum and antenna offset.
2. Restore meaningful portrayal
Return to a suitable compilation scale, review overscale indication, layers, palette, safety contour, isolated dangers and display category.
3. Check the route
Run the route check with correct vessel parameters, then inspect each alert and the source-quality or caution information rather than accepting an empty alert list.
4. Seek independent evidence
Use identified radar or visual marks and a properly interpreted depth trend where appropriate; the tablet does not independently verify its shared GNSS feed.
5. Exercise the backup
Confirm the crew can continue safely after loss of display, power, GNSS, network or chart entitlement instead of merely listing backup equipment.
Sense check: If both screens jump together when one GNSS antenna is displaced, the second screen supplied display redundancy but no independent position evidence.
Common mistake or limitation
- Calling any vector chart on any plotter an ENC or calling any chart display ECDIS without checking official data, approval, configuration and carriage context.
- Treating sharper zoom as additional survey detail and overlooking an overscale or compilation-scale warning.
- Assuming alarms prove a route safe when safety settings, layers, datum, source quality or vessel parameters may be wrong.
- Counting a second display on the same sensor, power and data chain as an independent navigation cross-check.
- Naming paper or another device as backup without keeping it current, accessible and usable by the watch.
Recap
- Raster and vector describe data structures; ECDIS describes a regulated system and operating context.
- Zoom and portrayal can change what is visible without adding source detail.
- Alarms are conditional on data, settings, sensors and correct vessel parameters.
- Agreement between displays is weak evidence when they share the same inputs.
- A backup must be current, independent enough for the failure and usable by the crew.
Optional quick check
Section 8 of 8
Two displays agree exactly because both receive the same GNSS and route from one gateway. What has that agreement proved?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Charts & Publications
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