The United Kingdom Hydrographic Office (UKHO) has
disclosed details of a new Electronic Navigational Chart (ENC)
which could help to improve situational awareness and
Developed to cover an area of the Bristol Channel known as 'The
Bridge', this 'high density' ENC displays depth contours at
one-meter intervals, allowing ECDIS to set safety contours at
corresponding levels to support navigation through shallow water.
ECDIS will select safety contours based on a safety contour depth
value set by the mariner. As most charts contain depth contours
at intervals of 2, 5, 10, 20 and 30 meters, ECDIS will sometimes
have to set a safety contour at a deeper interval than the value
set by the mariner. As a result of this, ships navigating in
shallower areas like 'The Bridge' have had to cross the safety
contour and override ECDIS alarms, as they have more clearance
than indicated. Disabling these alarms not only increases
administrative burden and alarm fatigue, but also means that
alarms will not indicate if the ship is actually approaching
depths of insufficient under keel clearance.
To overcome this challenge, the UKHO has been working with
partners to adapt this ENC to include one-meter depth contours.
In addition to safety benefits, this could also bring a
significant commercial benefit to cargo owners and ship and port
operators, as ships can be more confident about the true depth of
water under the keel - thereby increasing ships' cargo-carrying
To create the ENC, the UKHO worked with the manufacturers of
their cartography software to develop a new tool that
automatically processes billions of bathymetric data points (that
are delivered through highly accurate, multibeam sonar surveys)
to draw one-meter contours. These are then confirmed within the
software to ensure compliance with strict international standards
for all ECDIS systems. Finally, these are manually checked by a
cartographer to confirm accuracy.
This charted area with high density contours was then issued
digitally through the ADMIRALTY Vector Chart Service (AVCS),
allowing safety contours at key areas to be drawn by ECDIS with
one-meter accuracy. This helps to reduce stress on the bridge and
can give crews a greater degree of confidence on the approach for
the safety of cargo and ship.
Chris Berkley, a Master Mariner and Product Manager at UKHO,
commented: "Marking depth contours at five-meter intervals made
complete sense when it was being drawn by hand on paper or read
off a physical chart by a mariner - one-meter contours can be
close together and confusing when applied over wide areas. The
advantage of digital navigation on ECDIS is that we can now
switch from five-meter contouring to higher density one-metre
contouring in areas where it is useful.
"During this project, UKHO's hydrographic database team developed
a tool that fits into our business-as-usual charting methods to
create an ENC for a geographic feature called 'The Bridge' in the
Bristol Channel and Severn Estuary. In this location, silt
collects to form an area of water that is far shallower than the
rest of the channel. Ships must pass over 'The Bridge' to get to
the Ports of Bristol or Gloucester.
However, even though most ships can safely transit this area, it
is beyond the safety contour for many commercial ships.
Effectively, ships entering the Port of Bristol need to knowingly
ignore their training and cross the safety contour - setting off
multiple alarms, causing lots of disruption, and creating
significant paperwork for the master to explain.
"With the new and now in-use AVCS ENC for this area, we have
solved this problem and masters and pilots can now navigate the
area safely and in accordance with the rules on safety contours."
The UKHO is now extending the format to other ports and channels
in the UK and around the globe which are experiencing similar
challenges, thereby supporting greater navigational safety and