Tag Archives: AIS NMEA

How to decode AIS sentences !AVDM !AVDO

So you would like to decode NMEA AIS sentences of the type !AVDM and !AVDO


The best thing is to use one of the free available programs to decode AIS messages we listed here.

But if you want to do this on-line, you have some on-line tools where you can paste the messages that you would like to decode. These are NMEA 0183 messages:

And if you would like to dig in further and build your own decoder, there is available information here:

AIS receiver (AIS decoder hardware) Simple to install and connect with a USB cable

AIS decoder hardware. Simple to install and connect with a USB cable

How to connect AIS receiver or transponder to OpenCPN software

As you probably know the AIS receivers generate NMEA sentences.

In other posts we have presented the excellent software for navigation OpenCPN that more and more sailors are using as their main chartplotting solution on board. This open source software is available for Windows, Linux and Mac OSX.

In the latest version 3.2 there are significant improvements for AIS data processing.

Today we will focus on the installation and configuration procedure.

1. Connecting the AIS receiver to the chart plotting software OpenCPN

If the AIS receiver has USB connection, like for example the True Heading AIS RX Carbon, then it is very straight-forward.

If it has a serial connector (DB9 RS232), then you will normally have to use an adapter, because modern computers do not feature serial ports anymore. These have been replaced by USB ports.

We can recommend any Prolific chipset based converter, there are a lot of generic brands. Or if you want to search for a specific model, Belkin offers a few.

2. Configuring OpenCPN

You should follow the same guide used to configure a GPS, because basically as the GPS uses NMEA sentences, it works similarly to an AIS receiver. You can find them here http://opencpn.org/ocpn/setting_up_gps. This example is based on Windows. Basically you have to identify what is the COM port being used by the USB serial converter.

There is additional info in this page http://opencpn.org/ocpn/data_connections. You will see that the example is based on Linux.

3. Plotting AIS targets

The result of decoding the AIS data can be shown in the charts, as seen in the below image:

OpenCPN navigation software AIS decoding example view

OpenCPN navigation software AIS decoding example view

And a lot of configuration options are available, as described in the manual here: http://opencpn.org/ocpn/ais