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 before 2012.
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.
ENC
data must be used where it is available, but, where ENC data is not
available; Raster Navigational Charts (RNC) may be used with the
ECDIS in the Raster Chart Display System (RCDS) mode. However, when
operating in RCDS mode, the RCDS must be used in conjunction with an
appropriate folio of up-to-date paper charts.
Further
guidance on the use of ECDIS with ENC or RNC data is contained in
Annex 14 of the MCA SOLAS V publication and Marine Guidance Note
currently MGN 285.
ENCs
:
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.
RNCs
:
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. Further information on
ECDIS and RCDS can be found in Annex 14 of the MCA publication
“Safety of Navigation – Implementing SOLAS Chapter V 2002”.
This Annex also contains the text of IMO SN Circular 207 “Differences
between RCDS and ECDIS”
Compliance
with latest IHO 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.
ECDIS
Alarms and Indicators :
ECDIS
should give alarm and or indication as per following table;
Errors
/ Events
|
Alarms
/ Indications
|
| Crossing safety contour | Alarm |
| Area with special conditions | Alarm or Indication |
| Deviation from route | Alarm |
| Positioning system failure | Alarm |
| Approach to critical point | Alarm |
| Different geodetic datum | Alarm |
| Malfunction of ECDIS | Indication |
| Default safety contour | Indication |
| Information over scale | Indication |
| Large scale ENC available | Indication |
| Different reference system | Indication |
| No ENC available | Indication |
| Customized display | Indication |
| Route planning across safety contour | Indication |
| Route planning across specified area | Indication |
| Crossing a danger in route monitoring mode | Indication |
| System test failure | Indication |
| Alarm or Indication | Indication |
Alarm:
An alarm or alarm system which announces by audible means, or audible
and visual means, a condition requiring attention.
Indicator:
Visual indication giving information about the condition of a system
or equipment.
ECDIS
Integration :
Electronic
chart systems are integrated with the GNSS, 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. (See also “Chart Radar” in
paragraph 3.10 above.) 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.
System
based datum conversions :
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 manufacturers instructions should
always be carefully consulted to ensure correct system operation.
The
five mandatory alarms (indicated by audible means or audible and
visual means indicating a condition requiring attention) are:
i.
crossing safety contour;
ii.
deviation from route;
iii.
positioning system failure;
iv.
approach to critical point; and
v.
different geodetic datum.
Chart
objects and information available for display are sub-divided into
three categories:
•
base
display;
•
standard
display;
•
all
other information.
The
Safety Contour, Safety Depth, Shallow Contour, Deep Contour set by
the user.
Unlike
paper charts where source data diagrams are mostly provided, ENCs
(Electronic Navigation Charts) do not provide this information.
Instead they provide the navigator with a facility to examine
reliability and quality of source data by means of CATZOCs (Category
of Zone of Confidence). This gives an estimate of the reliability of
data related to five quality categories for assessed data (CATZOC A1,
A2, B, C and D) and a sixth category for data which has not yet been
assessed. It is also recommended to consider these CATZOC features
while determining a ship‟s safety settings.
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