Practical Navigation Course
Unit 3 · Electronic & Radionavigation

Chapter 14: Electronic Charts and ECDIS

ECDIS with official vector charts can replace paper under SOLAS, but only when set up, updated and backed up correctly. Most ECDIS incidents are configuration failures, not equipment failures.

Raster versus vector

A raster navigational chart (RNC, S-61) is a scanned image of the paper chart: familiar, complete, but a dumb picture that cannot warn, query or reorient sensibly. A vector electronic navigational chart (ENC, S-57 and increasingly S-100/S-101) is a database of objects with attributes, so the system can query a feature, adjust display density, and generate anti-grounding alarms. Only ENCs in an ECDIS satisfy full SOLAS chart carriage; RNCs are used in RCDS mode with an appropriate folio of paper charts.

Safety settings

Safety depth shades soundings shallower than the value and controls the display of dangers; safety contour is the boundary the system uses for anti-grounding alarms and is taken as the next available charted contour at or deeper than the value set. Shallow and deep contours shape the four-colour depth display. These values must be computed from draft plus under-keel clearance allowance and set deliberately for each passage — a default setting is a hazard.

  • Safety contour drives grounding alarms — set it, never accept the default
  • Check the look-ahead sector and alarm settings for each leg
  • Confirm ENC updates are applied and check for permit expiry

Backup and overreliance

SOLAS requires adequate independent back-up arrangements: a second, independently powered ECDIS on its own chart folio and position input, or an appropriate folio of paper charts. Do not overlay so much information (AIS, radar, weather, ENC layers) that the display becomes unreadable. Verify the ECDIS position against an independent source — radar range and bearing to a charted object — at regular intervals.

Key takeaways

  • • ENC/S-57 vector data in ECDIS satisfies chart carriage; raster charts do not on their own.
  • • Safety contour, not safety depth, drives anti-grounding alarms.
  • • Independent back-up arrangements and independent position checks are mandatory habits.

Knowledge check

Immediate feedback with rationales. Answer each question to see the explanation.

Chapter 14 quiz

0 of 3 answered

  1. 1.The ECDIS setting that governs anti-grounding alarms is the:

  2. 2.Operating with raster charts in an ECDIS (RCDS mode) requires:

  3. 3.A key advantage of vector ENCs over raster charts is that they: