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

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How do we use Waypoints Safely?

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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?

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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?

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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…