Charts

Additional amendments were made in 1998 by resolution MSC 86 (70) to permit operation of ECDIS in RCDS (Raster chart) mode.

IMO's Maritime Safety Committee (MSC), at its 73rd session from 27 November to 6 December 2000 adopted a revised Chapter V (Safety of Navigation) of SOLAS which enters into force on 1 July 2002.

Regulation 19 of the new Chapter V - Carriage requirements for shipborne navigational systems and equipment allows an electronic chart display and information system (ECDIS) to be accepted as meeting the chart carriage requirements of the regulation.

The regulation requires all ships, irrespective of size, to carry nautical charts and nautical publications to plan and display the ship's route for the intended voyage and to plot and monitor positions throughout the voyage. But the ship must also carry back up arrangements if electronic charts are used either fully or partially.

Performance standards for electronic charts were adopted in 1995, by resolution A.817(19)), which was amended in 1996 by resolution MSC.64 (67) to reflect back-up arrangements in case of ECDIS failure. Additional amendments were made in 1998 by resolution MSC 86 (70) to permit operation of ECDIS in RCDS mode.

Raster chart performance standards

The MSC, during its 70th session from 7-11 December, 1998, adopted performance standards for Raster Chart Display Systems, through amendments to the performance standards for electronic chart display and information systems (ECDIS), to allow the systems to be used with raster charts where vector electronic chart systems are not available.

A raster chart is basically just a visual scan of a paper chart. It is a computer-based system which uses charts issued by, or under the authority of, a national hydrographic office, together with automatic continuous electronic positioning, to provide an integrated navigational tool.

A vector chart is more complex. Each point on the chart is digitally mapped, allowing the information to be used in a more sophisticated way, such as clicking on a feature (for example, a lighthouse) to get all the details of that feature displayed.

The international standard for vector charts has been finalised by the International Hydrographic Organization (S-57, Version 3), and IMO adopted performance standards for ECDIS, using vector charts, in 1995 by Assembly Resolution A.817(19).

The amendments to Resolution A.817(19) state that some ECDIS equipment may operate in Raster Chart Display System (RCDS) mode when the relevant chart information is not available in vector mode.

The amendments to the ECDIS performance standards indicate which performance standards for vector charts apply equally to raster charts, and add specific specifications for raster charts, covering such aspects as display requirements, alarms and indicators, provision and updating of chart information and route planning. The amendments state that when used in RCDS mode, ECDIS equipment should be used together with an appropriate folio of up-to-date paper charts.

The MSC during its 70th sessionalso agreed a Safety of Navigation Circular on Differences between Raster Chart Display systems (RCDS) and Electronic Chart Display and Information Systems (ECDIS).

All ships are required to carry "adequate and up-to-date charts" under SOLAS Chapter V (Regulation 20) to assist in navigation.

Hydrographic data and charts

In 1983, IMO adopted a Resolution referring to the importance of the provision of accurate and up-to-date hydrographic information to safety of navigation and to the fact that many areas had not been surveyed to modern standards.

The Resolution invited Governments to conduct hydrographic surveys and co-operate with other Governments where necessary. This was followed in 1985 by a Resolution urging IMO Member Governments to establish regional hydrographic commissions or charting groups and to support groups already set up by the International Hydrographic Organization (IHO) to prepare accurate charts.

The Resolution was adopted after representation from the IHO, which had informed IMO of the inadequacy of nautical charts of many sea areas as a result of dependence on old hydrographic surveys and noted that, in order to develop up to date charts for these areas, substantial technical co-operation would be required between developed and developing coastal states on a regional basis.

In the revised chapter V of SOLAS, entry into force 2002, Regulation 9 Hydrographic services states:

Contracting Governments undertake to arrange for the collection and compilation of hydrographic data and the publication, dissemination and keeping up to date of all nautical information necessary for safe navigation.

In particular, Contracting Governments undertake to co-operate in carrying out, as far as possible, the following nautical and hydrographic services, in the manner most suitable for the purpose of aiding navigation: .1 to ensure that hydrographic surveying is carried out, as far as possible, adequate to the requirements of safe navigation; .2 to prepare and issue nautical charts, sailing directions, lists of lights, tide tables and other nautical publications, where applicable, satisfying the needs of safe navigation; .3 to promulgate notices to mariners in order that nautical charts and publications are kept, as far as possible, up to date; and .4 to provide data management arrangements to support these services.

Contracting Governments undertake to ensure the greatest possible uniformity in charts and nautical publications and to take into account, whenever possible, relevant international resolutions and recommendations. (refers to the appropriate resolutions and recommendations adopted by the International Hydrographic Organization.
Contracting Governments undertake to co-ordinate their activities to the greatest possible degree in order to ensure that hydrographic and nautical information is made available on a world-wide scale as timely, reliably, and unambiguously as possible.

SN/Circ.207 7 January 1999

DIFFERENCES BETWEEN RCDS AND ECDIS

The Maritime Safety Committee, at its seventieth session (7 to 11 December 1998), adopted amendments to the performance standards for Electronic Chart Display and Information Systems (ECDIS) to include the use of Raster Chart Display Systems (RCDS).
These amendments permit ECDIS equipment to operate in two modes: .1 the ECDIS mode when ENC data is used; and .2 the RCDS mode when ENC data is not available. However, the RCDS mode does not have the full functionality of ECDIS, and can only be used together with an appropriate portfolio of up-to-date paper charts.
The mariners' attention is therefore drawn to the following limitations of the RCDS mode:
.1 unlike ECDIS where there are no chart boundaries, RCDS is a chart-based system similar to a portfolio of paper charts;

.2 Raster navigational chart (RNC) data, itself, will not trigger automatic alarms (e.g. anti-grounding). However, some alarms can be generated by the RCDS from user?inserted information. These can include:

- clearing lines

- ship safety contour lines

- isolated dangers

- danger areas

.3 horizontal datums and chart projections may differ between RNCs. Mariners should understand how the chart horizontal datum relates to the datum of the position fixing system. In some instances, this may appear as a shift in position. This difference may be most noticeable at grid intersections and during route monitoring;

.4 chart features cannot be simplified or removed to suit a particular navigational circumstance or task at hand. This could affect the superimposition of radar/ARPA;

.5 without selecting different scale charts, the look-ahead capability may be somewhat limited. This may lead to some inconvenience when determining range and bearing or the identity of distant objects;

.6 orientation of the RCDS display to other than chart-up, may affect the readability of chart text and symbols (e.g., course-up, route-up);

.7 it may not be possible to interrogate RNC features to gain additional information about charted objects;

.8 it is not possible to display a ship's safety contour or safety depth and highlight it on the display, unless these features are manually entered during route planning;

.9 depending on the source of the RNC, different colours may be used to show similar chart information. There may also be differences in colours used during day and nighttime;

.10 an RNC should be displayed at the scale of the paper chart. Excessive zooming in or zooming out can seriously degrade RCDS capability, for example, by degrading the legibility of the chart image; and

.11 mariners should be aware that in confined waters, the accuracy of chart data (i.e., paper charts, ENC or RNC data) may be less than that of the position-fixing system in use. This may be the case when using differential GNSS. ECDIS provides an indication in the ENC which allows a determination of the quality of the data.

4. Member Governments are requested to bring this information to the attention of the relevant authorities and all seafarers for guidance and action, as appropriate.