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Raymarine forum - [LW11] AIS Target time out quest

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Full Version: [LW11] AIS Target time out quest
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Hi All,

I am after a little more in depth information in regards to AIS targets on a LH2 display v19.03.


History
We replaced a C90 Classic that had failed, with a c95. It is networked with via STng and Raynet to a Quantum. The only STng data is AIS from a Vesper XB8000

transceiver. The S series Auto pilot and ST instruments go through a STng to ST1 converter.

What is occurring is that even though AIS seems to be working, the c95 will intermittently drop targets. The Vesper XB8000 is also WiFi to the iPad and is showing Targets.

The issue is...

While the c95 is dropping the odd target, the iPad is maintaining them.
The customer stated that he never had any dropouts with his C90. Under the instruction of our Raymarine guys I collected data (using the Kvaser and logging)

submitted this to them for inspection. I have also viewed the data live.
Raymarine have stated that it is operating correctly. The data flow is consistent with transmission periods as per vessel/Class and speed.

My question is
how long does a target stay on the screen per vessel transmission. So if a cruise ship is anchored off the coast..should the target icon stay on the screen for the 3min until (stationary transmission) it receives the next update?
This particular target was apx 2+ nm away.



Thank you for your assistance

Garry.
Dear Garry71118,

Thank you for your query.

The Vesper XB8000 is a little vague but simply based around 2W of power the report rate (refresh rate) is every 30 sec > 2 knots or 3 min < 2 knots.

The AIS unit is most likely using CSTDMA (Carrier Sense Time Division Multiple Access) protocol which is used primarily for pleasure boating (Class B). The CSTDMA method uses carrier-sensing to defer transmissions until no other stations are transmitting. If a free slot is found, the transmission starts. Than the transmission is stopped for a 30 second time interval before the next one starts. Newer AIS units use SOTDMA (Self Organised Time Division Multiple Access) and will take precedence over CSTDMA.

This simply sounds like a timing issue.

Best Regards
Louise
Hi Louise,

Thank you for your replay.

The only change in this network was primarily the MFD, the AIS was placed in the network and working with the C80.

My particular question is how long does a target stay on a LH2 MFD. What (if anything) would cause a target to disappear before the next receive. Is there any reason that would cause them disappear?

Thank you

Garry.
Hi Garry71118,

Thank you for your query.

A target can remain on the screen for up to 7 minutes before being removed with no update. Other causes for them to disappear is the the AIS being put in to silent mode or being switched off.

Many Thanks
Louise
Hello,

So since our last chat we have had a very long extended wet season.

This 7 minute window for a target to stay on the MFD, is this time period also the same for the secondary data (6 minute static data)?

once the static data has been received through the Vesper AIS it is displayed on the iPad, and sometimes not on the MFD

One target that he was monitoring showed its icon as a particular boat but would then switched back to a triangle (unknown boat type).

Wouldn't this data stay with the MMSI number on the MFD?


Thank you
Dear Garry71118,

Thank you for your response.

Due to continual issues with the Vesper AIS, we do not support the integration of the Vesper AIS with our system.

The Vesper has very long timeouts on AIS targets on their own app of which makes it appear the MFD has a problem when in face the Vesper app is continuing to show invalid data.

Please contact Vesper with any queries relating to target data.

Many Thanks
Louise
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