When an electronic chart is loaded into the system it is reformatted to the system-specific format in its database SENC (System Electronic Navigational Chart). S-57 is not appropriate for use in real time. Some retailers can supply charts in SENC format, which saves time and saves the Navigator from any problems that may occur during reformatting.
ECDIS contains a list and an overview of the cells that are loaded in SENC, their correction status and their period of validity. Both navigation program and ENCs must be up-todate in order to be an ECDIS.

Many components must cooperate in order to correctly show an electronic chart on the screen. The navigation program, coding of information in S-57 (not all nations interpret the rules in the same way), selection of the correct screen symbol from the Presentation Library, and so forth. Compatibility problems may arise with different versions. Rebooting the navigation program now and again is also a wise precaution.

’’Recent preliminary investigation indicates that some ECDIS may not display certain combinations of chart features and attributes correctly and on rare occasions may fail to display a navigationally significant feature. This appears to be caused by anomalous behaviour in some ECDIS software, especially early versions. The existence of such anomalies highlights the importance of maintaining ECDIS software to ensure that operational capability and reliability are maintained. It is recommended that appropriate checks are made with the equipment manufacturer.This is of particular importance where ECDIS is the only source of chart information available to the mariner”

1. Test of ECDIS

The International Hydrographic Organisation (IHO) has started a project to investigate the quality of various ECDIS and identify possible problems. IHO has therefore put together two specially designed ENC-cells (AA2TDS02 and AA5DS05) which can be used to test the functioning of the ECDIS system on board. The two ENC cells have been delivered to ECDIS vessels in the same way as new ENC cells and they can also be downloaded from the IHO web page (www.iho.int), which also has a protocol to report the results of the test. The test files (Check ENCs), the protocol and instructions for installing and using the test files can be found under "IHO News" in the right-hand margin.

2. Distribution of official electronic charts

Sales of official electronic charts are built up around an organisation based on publishers, (usually the Maritime Administration of the country) - storage centres - authorised sales outlets- users. Each nation surveys its own waters and sends the results to the sales organisation. 

To make the global distribution of ENC easier, the IHO has taken the initiative to set up RENC (Regional ENC Coordination Centres). Each RENC is a non-profit making organisation controlled by its member states for the distribution of its ENCs. At the time of writing (2015) two RENCs exist, one in Norway (Primar, twelve member countries), the other in Great Britain. ENCs are only sold by authorised distributors, who also supply information about corrections.

Official ENCs are sold by subscriptions for a certain period, including weekly corrections. When a navigation system is used as an "aid to navigation" a portfolio of charts are needed, (if two indepenent ECDIS systems have not been installed).     

      Overview of cells in ECDIS (SAM)

There are a variety of systems for subscribing to electronic charts (2015).

• The first system in use was an annual subscription for a number of ENCs but these days threesix-month and twelve month subscriptions are also available (Direct Licensing).
• A vessel pays only for those ENC that are used (Dynamic licensing). 
• Free access to all ENCs for planning purposes. During the voyage the vessel's position is continuously reported and the supplier invoices for those charts that have been used. The system makes it possible to buy access to more electronic charts if the destination is changed during the voyage (Pay-as-yousail).
  

The purchase of a subscription for official ENCs enables access to all ENCs that exist, supplied on CD or DVD discs. These have a basic disc and a corrections disc. In addition a password is supplied to access the electronic charts in the subscription.

Every electronic chart has a number, which consists of: a publishing code, usage (overview-harbour, 1-6), cell number, version number (after correction).

    DVD with 12000 electronic cherts from UKHO

The function for Helectronic cherts for the voyage" from Primer-online (Adveto)

A downloading problem
The day before, the ship requested that the ship management company purchase electronic navigational charts (ENC) covering the approach to Sunndalspra. The codes for the electronic charts were ordered by the ship management company from its regular chart distributor in Canada on 23 September 2008. Within 24 hours, the ship received an e-mail with the necessary codes to open these charts. The bridge crew attempted to install the charts, without success. ARCS (Admiralty Raster Chart Services - overview charts) were ordered on the same day, and these were installed.
(Norwegian report on FEDERAL KEVALINA, see page 397)

With a plotter it is possible to see which charts are installed by increasing the scale past a certain value. Note that not all installed charts are necessarily usable for navigation, as their scale may be too smal

The slot for an electronic chart chip in a plotter. There is also a connector for a USB-contact

Unofficial electronic charts, either rastered or vectorised, are sold by ship's chandlers and instrument suppliers. Depending on the operating hardware they are supplied on memory sticks  (for plotters) or CDs.