The mariners' attention is drawn to the following limitations of the RCDS mode:
1 Unlike ENC, where there are no displayed boundaries, RNCs are based on
paper charts and as such have boundaries which are evident in ECDIS;
2 RNCs will not trigger automatic alarms (e.g. anti-grounding). However
alarms and indications can be generated with the manual addition, during passage
planning, e.g. of clearing lines, ship safety contour lines, isolated danger markers and
danger areas to mitigate these limitations;
3 Horizontal datums and chart projections may differ between RNCs. Mariners
should understand how a chart's horizontal datum relates to the datum of the position
fixing system in use. In some instances, this may appear as a shift in position. This
difference may be most noticeable at grid intersections;
4 A number of RNCs cannot be referenced to either WGS-84 or PE 90 geodetic
datums. Where this is the case, ECDIS should give a continuous indication;
5 The display of RNCs features cannot be simplified by the removal of
features to suit a particular navigational circumstance or task at hand. This could
affect the superimposition of radar/ARPA;
6 Without selecting different scale charts the look-ahead capability may be
limited. This may lead to inconvenience when determining range and bearing or the
identity of distant objects;
7 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);
8 It is not possible to interrogate RNC features to gain additional
information about charted objects. Whether using ENC or RNC, in the planning process a
mariner should consult all relevant publications (such as sailing directions, etc.);
9 With RNC, 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;
10 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
night time;
11 An RNC is intended to be used at the scale of the equivalent paper chart.
Excessive zooming in or zooming out can seriously degrade the displayed image. If the
RNC is displayed at a larger scale than the equivalent paper chart, the ECDIS will
provide an indication; and
12 ECDIS provides an indication in the ENC which allows a determination of
the quality of hydrographic the data. When using RNCs, mariners are invited to consult
the source diagram or the zone of confidence diagram, if available.