AIS receiver gets slower over time - lagging display

[MM5AHO]

I have an AIS receiver (only receiver, no transmitter), and I link it to my notebook on which I run SeaClear charting software. There's also a GPS input to the notebook.

I notice that after a few hours, the AIS positions showing on the chart are lagging by several minutes, sometimes as much as 10 mins. This means the AIS transmitting boats showing on the chart are not where they're shown, they're some way ahead of that.

If I disconnect the AIS input, then reconnect, it gets back to showing real time, then starts over time to lag again.

The connection from AIS to notebook is via a serial to USB converter, as is the GPS input. Both feed into one each of 9 pin serial plugs, which combine into a single USB plug that plugs into the notebook.

I don't rely on the AIS info, so timing isn't critical, but its just curiosity that makes me want to know who is who, and what speed they're doing.

Notebook is ASUS EeePC, OS is Win7

Any ideas?

 

[knuterikt]

What's the speed on your virtual serial ports?
suspect problem is on the PC or serial to USB

Edit:
My guess is that the AIS receiver is not causing this

 

[Martin_W_Brown]

As a computer programmer my first suspicion would be a resource leak - something is using memory or files and not releasing them when done. Easy to do and tricky to track down. Because it take a few hours for the symptoms to appear the software may never have been tested for long enough.

It might be triggered by the serial connection system you are using or it might just be a problem in Sea Clear. Worth reporting to Sea Clear - they may be able to find and fix the bug.

 

[BrianH]

You could try with OpenCPN (free), install and set the com port number, then invoke the NMEA debug window. It will display the messages as they arrive. The program can display both raster and vector charts but for debug, none will be needed.
http://opencpn.org/ocpn/

I run OCPN on a small Acer Aspire with Win 7 Home and it works flawlessly with an AIS receiver with integrated GPS fed on the same USB input via a serial/USB adapter. But whatever you use now can be set in the Options>Connections setup.

 

[SteveMB]

As a fellow programmer - I agree with Martin when he says

As a computer programmer my first suspicion would be a resource leak - something is using memory

I Have had similar problems trying to display AIS data using an (older) Asus EeePC running XP. I found that various navigation programs would work fine - until I enabled the processing of AIS data - at which point the programs would run slow or crash. I believe there just isn't the necessary processing power available - so the AIS input is being processed as fast as the PC can - but that's not "real time".
The fact that removing the input for a while - allowing the PC to "catch up" with the data that has been received but not yet processed - would tend to support that hypothesis. Especially as the same software on a more powerful laptop works flawlessly.
I have found that OpenCPN doesn't seem to need as much processing power - and will work on the little ASUS.
Hope that helps.

 

[ianj99]

Download the free Navmonpc utility which has a useable AIS radar display and does not suffer from any lag. If this works without lag on your setup, its not the hardware but maybe Seaclear.
If the lag is apparent with navmon, then it maybe a usb/serial issue but would be unusual I would suggest.

http://navmonpc.com

You could set the connection to just get the AIS data which it will and display as a list, though the radar display needs your location for it to work. Alternatively, you can route all the data through navmon using its NMEA routing ablity.