safer use of electronic aids to navigation anzsbeg
TRANSCRIPT
Safer use of Electronic Aids to Navigation
ANZSBEG
Why are these charts different?
© Hydrographic Office
NOT to be used for Navigation
Electronic charts are produced by tracing official paper charts – accuracy depends
on who traces them
Traced charts are called Vector charts and can be viewed on all these displays…
There is another type of Electronic Chart; a ‘Raster’ Navigational Chart (RNC)
‘AusRNC’ – are scans of Official Paper Charts produced by the Hydrographic Office
They can only be viewed on Computer based software
They cannot be viewed on Plotters They are more expensive
But how accurate are the paper charts they are created from?
© Hydrographic Office
NOT to be used for Navigation
Was this chart surveyed by ‘Flinders’ using a lead line? ... or a surveyor using the latest technology?
‘A Zone Of Confidence’ diagram indicates how the survey was conducted – the letters indicate
different methods of survey – A1 is bestThis was previously known as ‘Source Data’
‘Zone’ C is quite common
but how accurate is this?
Zone Of Confidence diagrams can be viewed on all ‘Raster’ Charts as they are simply a scan of
the whole Official chart
On ‘Vector’ charts this is rare so makes it difficult to identify the quality of survey conducted
Before using Vector Charts try to view an Official Paper chart and identify the accuracy of survey
ANZSBEG
Survey’s are conducted with reference to a datum point; these points being known
as Horizontal Datum’s
WGS 84 is a ‘Horizontal Datum’
used by GPS Satellites
A Horizontal Datum is often marked by a plate on the ground that positions are measured from (there is one under the tripod in this picture)
Older Charts were surveyed to a ‘Horizontal Datum’ named AGD 66
Many of these charts have been re-aligned to WGS 84
Look for this information on your Paper Charts
WGS 84 vs. AGD 66
Selecting the wrong Datum will shift your
position on the screen
In Australia, the difference between
WGS 84 and AGD 66 is about 180metres
Some Maritime Authorities have placed markers to confirm if your equipment is
set to WGS 84 Datum
If the value is small this indicates you are on the correct Datum
– nothing more
It’s useful to enter these as Waypoints for future
reference
Before using a GPS receiver check the ‘Datum’ matches the datum on
the chart you are using
ANZSBEG
How do we use Waypoints Safely?
ANZSBEG
If you need to transfer Waypoints from Paper Charts to Electronic equipment• Leave Plotters / GPS units set to WGS 84 datum• If the paper chart has a different Horizontal Datum you
should see this box …
• This provides the ‘position shift’ for plotting a GPS derived co-ordinate on a paper chart
• The opposite direction will apply if transferring from Paper to Electronic Chart
When placing Waypoints (especially as part of a route) zoom in and check for hazards
When creating ‘Routes’ it’s easier to zoom out and view the whole passage on the chart
This results in less detail being displayed
Waypoints may be placed too close to hazards
Zoom in on each waypoint and move accordingly
Wolf Rock- QLD
When using GOTO Waypoint avoid using a ‘heading marker’
It can hide other hazards – there is a rock under this heading marker
When using ‘routes’ take care when using Auto-selection of Waypoints; it may cause you to cut a corner – try using manual
selection and be aware of the Waypoint Arrival Distance
What can go wrong when using Vector Charts and Displays?
ANZSBEG
A small powerboat was heading for a Waypoint in the Brisbane River using a ‘Rolling Road’ display
The Chart Chip used had not been updated and did not show changes to the sea wall
Update Vector Charts regularly and register for eNotices to keep
abreast of changes to your charts
ANZSBEG
eNotices is a free service available at www.hydro.gov.au
What else can go wrong?
ANZSBEG
This Yacht hit Flinders Island (NSW) at night by following the Chart
Plotter screen too closely – poor night vision and over-reliance were
contributing factors
With ‘Vector’ charts we can keep ‘zooming in’ until the boat fits through the gap – Zooming in and out can also affect the amount of detail displayed
Remember:Vector Charts are only as accurate as the Paper Chart they were traced from
Yacht Lamachan
Elizabeth Reef\
In August 2007 she grounded on Elizabeth Reef, a large drying reef to the north of Lord Howe Island while using GPS, a chart plotter and unofficial charts. The reef is six miles wide and is surveyed to a horizontal accuracy of better than 20 metres.
Extract of a Presentation by Mike Prince – Australian Hydrographic
Office
ANZSBEG
Example Incident
The yacht "Asolare" grounded on Moore Reefs at approx 0400 3 Aug 2008.
News Reporting
“Our chart didn't show any reef in that area at all“
Mr Peter Turner, Skipper of Asolare
Mr Peter Turner, Skipper of Asolare, safe after being rescued by helicopter
The Location
A section of AUS 4060 (INT 60) Australasia and Adjacent Waters, 1:10M, with Moore Reefs highlighted
The Response
“There has been some confusion about the charts being referred to in the articles. The main concern was the reef apparently not being shown on some electronic charts, the company subsequently issuing a warning notice.”
“In my mind there is nothing better than a paper chart, and all yachts are required to carry them. Unfortunately not everyone refers to them as much as they should nowadays.”
Andrew Bishop, Managing Director, World Cruising Club
Industry Response
Industry Response cont’d
Jeppesen Marine reminds navigators that nautical chart information is constantly changing.
National Hydrographic Authorities periodically publish new and updated information. As it is received, Jeppesen Marine incorporates the updated information into new and existing products. These changes are available to our customers to purchase.
Therefore navigators should check their Jeppesen Marine charting products to make sure that they have the most current version available. If your charts are outdated, Jeppesen Marine strongly advises you to update them via Jeppesen Marine directly or through authorized resellers.
Jeppesen electronic charts are an aid to navigation designed to supplement the use of authorized government charts, not to replace them. Only up-to date official government charts and Notices to Mariners contain all the information needed for safe navigation.
Another manufacturer
What can affect the accuracy of a GPS receiver?
ANZSBEG
GPS Reception depends on…
• How many Satellites are being received• Which Satellites are being used• If any Satellites are obscured by parts of the
boat or people• How sensitive the receiver is (many boats
have older, less sensitive receivers)
Horizontal Dilution Of Precision(HDOP)
Knowing what the HDOP value is can provide an insight to accuracy – some receivers display this in metres, not HDOP values
HDOP Value
1 Excellent
2-10 Good / Moderate
10-20 Discard / Poor
>20 Large inaccuracy
Summary• Consult Paper Charts before using
Electronic versions• Take care in placing Waypoints• Understand equipment defaults• Don’t assume that because it is Digital,
it must be accurate and you can trust it
the limitations of unofficial electronic charts,
upon which the fundamental navigation
functions are performed, must be clearly
understood
While the hardware may be great, and the display impressive…