Electronic Charts (ENC) and ECDIS Awareness

Electronic charts come in two main types. Raster Navigational Charts (RNCs) are essentially scanned images of paper charts — they look identical to the paper version but cannot be interrogated or re-scaled intelligently. Vector charts (Electronic Navigational Charts, or ENCs) store data as objects in a database, allowing the display to be customised, layers toggled, and individual features queried for additional information.

ENCs are the official digital equivalent of paper charts. They are produced by national hydrographic offices to the international S-57 (and newer S-100/S-101) standard. Because they are vector-based, the chart display can be zoomed without loss of clarity, and features like depth contours can be set to the vessel's draught, triggering automatic warnings.

ECDIS (Electronic Chart Display and Information System) is the IMO-approved system for displaying ENCs on commercial vessels. It integrates chart data with GPS position, radar overlay, AIS, and route planning. SOLAS vessels may now use ECDIS as the primary means of navigation, replacing paper charts on compliant vessels.

Despite the advantages of electronic charts, paper charts remain important as a backup. Electronics can fail — power loss, software errors, GPS jamming, or antenna damage can leave a vessel without electronic navigation. A prudent skipper carries paper charts for the passage area and knows how to use them.

A critical consideration with any chart is the horizontal datum. Most modern charts and GPS use WGS84 (World Geodetic System 1984). However, older paper charts may reference a different datum, which can introduce positional errors of up to several hundred metres. Always check the chart's title block for the datum used and apply any noted corrections before plotting GPS positions.