ECDIS is an integrated electronic navigation system which combines the data obtained from a number of electronic navigation sensors and displays it on a video display unit/monitor both in the form of a graphic image and alpha-numeric information. The sensors providing the data inputs to ECDIS are the following:

1. The global positioning system (GPS and/or DGPS).
2. The automatic identification system (AIS).
3. The radar and automatic radar plotting aid (ARPA).
4. The ship’s gyro compass.
5. The echo sounder.
6. The ship’s log.

The system makes use of electronic (digital) navigation charts (ENC’s) in place of the normal paper charts which they are intended to replace. The position of the ship is plotted in real time and kept continuously up to date. The ship’s track can be planned and plotted on the electronic chart either by use of the computer “mouse” and cursor or alpha-numeric keyboard. The voyage or passage plan can then be stored in the system’s memory and when retrieved and executed, provides the planned track as would be the case with a paper chart.

Being in digital format, the track is plotted on a seamless series of charts. In the case of paper charts, the position would have to be transferred to the next chart in the series as the vessel proceeded along its planned track. The system can be instructed to provide a plotted position at predetermined time intervals, as would be the case with paper charts when positions are plotted manually.

One can also set other navigational parameters in the system, ie the maximum allowable deviation from the planned track, safety depth contours, arrivals at predetermined waypoints, alter course positions, etc. When these parameters are breeched, or a vessel reaches the predetermined waypoints/positions, it activates a visual and audio alarm to alert the officer of the watch/ navigator.

The ship’s physical parameters (length, beam, draught, tonnage type and power of the engines, types of steering, manoeuvring characteristics, etc are also entered into the system so that it can predict the outcome of an intended manoeuvre, ie determining alter course positions.

Electronic charts can be constructed using either of two types of data, namely vector or raster. In the case of raster charts, a paper chart is scanned and converted to a digitised replica. This digitised image cannot be interrogated or changed, ie what is on the paper chart is displayed as is. In the case of the vector chart, all the information and symbols on the chart as well as their characteristics are digitally encoded individually and stored in the system’s data base. This enables the operator to decide what he wants displayed and the level of detail he requires. This is to prevent the display being cluttered with unwanted or unnecessary data. To make vector charts is more costly and more time consuming than raster charts. Because of this, it will still take some time before all charts are replaced with vector charts. Until then ECDIS will also allow the display of approved raster charts which comply with IMO performance standards. Whereas chart corrections and updating was carried out manually, the correction of Electronic Navigation Charts can be done off-line (by CD-ROM or diskette) or on-line (via radio links or internet).

In addition to the purely navigational aspect, the system is designed to allow the overlay of the radar/ARPA picture on the chart graphics. The rest of the information provided by ARPA and the AIS system is displayed next to the graphic display in alpha-numeric format. By looking at one video display unit/monitor the navigator or officer of the watch can observe all the information provided by the various navigation sensors, instead of looking at the data displays of each one individually in different locations. As in the case of the navigational mode, the system can be set to provide visual and audible alarms when a dangerous situation develops, ie a vessel on a collision course or having a CPA closer than. It is a wonderful navigational tool which will save the officer of the watch much time, especially in a congested seaway where he can apply himself more efficiently in keeping a proper lookout of his environment. There is always a danger, however, that he or she becomes complacent and relies too heavily on the system for watchkeeping, instead of using it as an aid to or enhancement of his/her physical/visual watchkeeping. The phenomenon when a collision has occurred despite the availability of electronic navigation systems has been referred to as an “electronically assisted collision”. One must always be aware of the possibility of a malfunction in the system and regular checks by an independentnavigational source must be conducted. One should also continuously reconcile the electronic picture with that obtained visually by the watchkeeper.

The International Maritime Organisation (IMO) decided that it will be mandatory for all seagoing commercial vessels to carry ECDIS. Implementation was carried out in phases commencing 1 July 2012.

It should be noted that not all Electronic chart Systems (ECS) are ECDIS and only an ECDIS approved by the IMO is approved for navigational use. It is also an IMOrequirement that a suitable and independent back=up navigation system be available in addition to the ECDIS.

Side by side displays of the radar picture and the electronic chart display.