SE CTION 1 THE OPERATION OF ELECTRONIC CHARTS

 

 

Types of Electronic Charts

 

 

G e neral

 

 

There are two basic types of electronic chart systems. Those that comply with the IMO requirements for SOLAS class vessels, known as the Electronic Chart Display and Information System (ECDIS), and all other types of electronic chart systems, regarded generically as Electronic Chart Systems (ECS). If an ECS is carried on board, the continuous use of up-to-date paper charts remains essential for safe navigation and to fulfill carriage requirements.

 

 

To satisfy the chart carriage requirements of SOLAS Chapter V, ECDIS must use Electronic Navigational Charts ENCs.  These are vector charts produced to International Hydrographic Organization standards and officially issued by or on the authority of a Government authorized Hydrographic Office or other relevant government institution. At present, ENC data is not available world-wide which limits the use of ECDIS in some areas. This situation, however, is rapidly changing and comprehensive ENC coverage of the world's major trading routes and ports is forecast to be completed in the near future.

 

 

The ENC contains all the chart information necessary for safe navigation, and may contain supplementary information in addition to that contained in the paper chart (e.g. sailing directions) which may be considered necessary for safe navigation.

 

On l y ENC are permitted to be used for navigation. Should ENC not be available for sections of the intended voyage then the vessel must use an up-to-date paper folio of corrected charts for navigation.

 

 

ENC

 

 

The ENC is a database of individual items of digitized chart data which can be displayed as a seamless chart. ENCs of appropriate detail are provided for different navigational purposes such as coastal navigation, harbor approach and berthing. The amount of detail displayed is automatically reduced when the scale of a particular ENC is reduced, in order to lessen clutter. Individual items of data can be selected and all relevant information will be displayed (for instance, all the available information relevant to a light or navigation mark).

 

 

ENCs are therefore very much more than an electronic version of the paper chart. With vector charts the data is “layered”, enabling the user to de-select certain categories of data, such as textual descriptions, which may clutter the display and may not be required at the time. It is also possible for the user to select a depth contour so providing an electronic safety contour which may automatically warn the watch-keeper when approaching shallow water. Mariners should use the facility to de-select data with extreme caution as it is possible accidentally to remove data essential for the safe navigation of the vessel.

 

 

RNC

The Raster Chart Display System (RCDS) uses RNCs, which are exact facsimiles of official paper charts, and for which Hydrographic Offices take the same liability as for their paper products. RCDS does not have the same functionality as ECDIS and thus an up-to-date folio of paper charts for areas not covered by ENC must be maintained for the intended voyage.

 

E CDIS Standards

ECDIS in operation comprises hardware, software and data. It is important for the safety of navigation that the application software within the ECDIS works fully in accordance with the Performance Standards and is capable of displaying all the relevant digital information contained within the ENC.

 

Any ECDIS which has not been upgraded to be compliant with the latest version of the ENC Product Specification or the S-52 Presentation Library may be unable to correctly display the latest charted features. Additionally the appropriate alarms and indications may not be activated even though the features have been included in the ENC. Similarly any ECDIS which is not updated to be fully compliant with the S-63 Data Protection Standards may fail to decrypt or to properly authenticate some ENCs, leading to failure to load or install.

 

ECDIS that is not updated for the latest version of IHO Standards may not meet the chart carriage requirements as set out in SOLAS regulation V/19.2.1.4.

 

The master must verify via the vessel’s superintendent that the ECDIS software installed is the latest version and in compliance with the standards. The superintendent is to seek clarification with the ECDIS manufacturer.

 

The IHO Standards that relate to ECDIS, ENC production and distribution, are listed below:

 

IHO ECDIS Standards	Current Edition
ECDIS Display and Presentation     Electronic Navigational Chart (ENC)	S-52 6.1 S-52 Presentation library Annex A Edition 4.0   S-57 Edition 3.1, S-57 Edition 3.1.1 and S-57 Maintenance Document (Cumulative) Number 8
IHO Recommended ENC Validity Checks Raster Navigational Chart (RNC) ENC Producer Codes	S-58 Edition 6.0.0   S-61 Edition 1.0   S-62 Edition 11Jul 2017

 

 

ENC Data Protection	S-63 Edition 1.2.0
IHO Test Data Sets for ECDIS   ENC Production Guidance	S-64 Edition 3.0   S-65 Edition 2.1.0

 

 

A list of all the current IHO standards is maintained within the ENC/ECDIS section of the IHO website (www.iho.int) and can be found in Appendix 7 of this manual. Mariners should be aware that proper ECDIS software maintenance is an important issue and adequate measures need to be in place. This may be subject to verification during Port State Control inspections.

 

IHO Data Presentation and Performance checks:

The IHO has designed datasets that can help determine if the ECDIS software has any shortcomings or requires upgrading. The IHO data presentation and Performance checks must be carried out every

3 months on all the ECDIS sets.

 

 

In case there results of the ECDIS sets do not match the requirements set by IHO, the test results should documented by filling up the form “ECDIS Check reporting form” which is provided separately and should be sent by the vessel to the office. This form requires to be submitted by the vessel’s superintendent to IHO.

 

In case the vessel determines that the underwater features and isolated dangers are not displayed properly the vessel must inform the office and action must be taken to supplement the planning and monitoring of the route. This could be done by consulting other sources of information such as paper charts and publications to ensure that the watchkeepers can identify all underwater dangers and isolated dangers. These additional hazards can then be added manually in the ECDIS as a "manual update". The vessel can do this by using an appropriate mariner's data/ mariner's note or mariner's information functions of ECDIS.

 

 

Guidance for the test and the reporting form can be found in appendix 6 of this manual.

 

 

E CDIS Integration

Most modern ECDIS already integrate the majority of navigational systems on modern bridges but are subject to the condition that their integration does not degrade the performance of any equipment providing sensor inputs or the performance of ECDIS itself.

 

The benefits of integrating additional navigational systems will include providing the mariner with a greater perspective of the navigational picture whilst increasing situational awareness. The navigation officer’s work load decreases as information relating to the safe navigation of the ship (for example, depth, speed and course) can be readily viewed on the ECDIS display as well as other important information.

 

 

Electronic chart systems are integrated with the GPS, enabling the vessel’s position to be continuously displayed. Caution should be used in areas when raster charts cannot be referenced to WGS84. Electronic charts may also be integrated with the radar and electronically plotted data from ARPA, ATA or EPA, with part or all of the radar display overlaid or under-laid on the chart display.

 

 

There is a danger that the combined display may become over-cluttered with data. The overlay of target data on an electronic chart does not reduce the need for the targets to be observed on the radar display. Mariners should also exercise caution where target vectors based on the vessel’s water-track are overlaid on an electronic chart which displays the vessel’s ground track.

 

 

Electronic charts are becoming an essential part of the navigation system of a ship’s bridge and contribute greatly to navigational safety. However they must be used prudently bearing in mind the existence of unapproved equipment and the absence of official vector data in some regions.

 

 

Manufacturers of GPS receivers, ECDIS and ECS often incorporate a user selectable datum transformation capability into their software. This capability enables users to deal with datum differences in a systematic and apparently automatic manner. Whilst this might appear to be a good thing, considerable caution needs to be exercised.

 

 

A potential problem is that a single systematic transformation is not always accurate for large regional datums. A GPS receiver position (WGS84) transformed to a regional datum by means of an average set of shifts may differ from the GPS receiver position (WGS84) amended to the regional datum by the shift note on an individual chart. The shifts provided on an individual chart are calculated specifically for the chart and the area that it covers and will be more accurate than a set of generalized shifts.

 

 

Interfacing issues might also emerge when connecting a GPS receiver to an ECDIS or ECS, particularly if the GPS receiver is configured to convert its position output to a local or regional datum. Care must be taken to ensure that GPS receivers are configured to provide position in the datum that is expected by the ECS or ECDIS. In the majority of cases this will be the WGS84 datum, but manufacturer’s instructions should always be carefully consulted to ensure correct system operation.

 

 

Not all electronic charts are in same format; many different formats exist for electronic charts. However, two major types are now in use on merchant ships, they are vector chart and raster charts. Raster charts (RNC), in fact, are scanned paper charts into the pictures with adjustment made suitable for display on the RCDS. This RNC is also known as Admiralty Raster Chart System (ARCS Charts) which is produced by the British Admiralty.

Vector charts are digitized charts. Countries are producing unique digital charts based on their interpretation of IHO standards (i.e. S-57 standards).

Salient differences between two charts are:

 

 

RNC (RCDS or ECS)

E NC (ECDIS)

• Chart based system similar to paper charts. • Will not trigger automatic alarms. Some alarm can be generated from user-inserted information. • Chart projection may differ between RNCs. • Chart horizontal datum relates to the datum of the position fixing system, may appear as a shift in position. • Feature  cannot  be  simplified  or  removed  to  suit  a particular navigational circumstance. This affects the superimposed of radar/ARPA picture. • Cannot select different scale charts. • May affect the readability of chart text and symbols. • Not possible to gain additional information. • Not possible to display a ship’s safety contour or safety depth. • Different colours may be used to show similar chart information. • Displayed at the scale of the paper chart. Excessive zooming in or out can seriously degrade RCDS capability. • In confined waters, the accuracy of chart data may be less than that of the position fixing system in use.

• No chart boundaries. • Will trigger automatic alarms.

 

 

Limitation of ECDIS

 

 

It should be noted that the ECDIS is only a tool that helps a mariner safely and effectively navigate a ship.  One of the biggest risks with the transition to ECDIS is an over reliance in the information provided. Periodical checks and lookout must be performed and basic principles of watch keeping to be observed.

 

 

There are some limitations of the ECDIS:

Chart Accuracy

 

ECDIS provides the navigator with a tactical tool which incorporates a high accuracy positioning device.  The navigator can "zoom" in on an ECDIS chart to a scale beyond the intended accuracy of the charted information.

 

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