Electronic Charts (ENC) and ECDIS Awareness

Official Raster Navigational Charts (RNCs) are digital facsimiles of paper charts: their portrayal is fixed and they do not expose chart features as individual database objects. Electronic Navigational Charts (ENCs) are official vector datasets whose objects can be queried and displayed according to system settings. Commercial plotter charts may be vector or raster without being official ENCs.

Current ENC services have commonly used the IHO S-57 transfer standard; S-101 is part of the S-100 transition. Vector data can be interrogated and re-presented, but zooming beyond the compilation scale can create false confidence. Safety contour, display-category and alarm choices need a route check, not just a software default.

ECDIS is a performance-standard navigation system used with official ENCs and appropriate updates, sensors, settings and backup arrangements. A compliant installation can meet applicable SOLAS chart-carriage requirements, but an ordinary leisure chart plotter is not thereby ECDIS and an ENC display does not remove the need for lookout, position cross-checking or voyage planning.

Plan an independent, usable fallback for loss or corruption of position, power, display, sensors or chart data. Depending on the vessel and passage this may include current paper charts and manual methods, independent power and equipment, or another approved arrangement; the point is to avoid a common-mode failure and to practice the fallback before it is needed.

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.