NemaStudio Actisense NGW-1 NMEA2000 gateway support

Actisense recently released (end 2009) two new NMEA2000 PC gateway products to the market: the NGT-1 and the NGW-1 (image at the left).

Both products have in common that they are both connected to a USB PC port on one side and to the NMEA2000 bus on the other side.

These devices are really great to hook up PC applications to the NMEA2000 bus and many marine software developers have already developed applications that interface with either one or both.

The difference between the NGW-1 and the NGT-1 is that the latter requires specific PC software to talk to the NMEA2000 network through a DLL provided by Actisense, while the NGW-1 can be seen as a converter between NMEA0183 and NMEA2000.

For the time being Sailsoft decided to not implement the NGT-1 in the current architecture of NemaStudio. The reason for this is that the specific power of NemaStudio is focused on simulating NMEA0183 sentences. Simulating NMEA2000 PGN’s requires a different approach, even when using the Actisense DLL library functions.

This is because a NMEA0183 sentence seldom can be translated 1:1 to a NMEA2000 PGN. Take for example the NMEA0183 RMB (Recommended Minimum Navigation) sentence. Parts of the contents of this sentence would go to PGN 129283 (XTE error) and other parts need to go into PGN 129284 (Navigation Data). But that is not all: the PGN 129284 also requires a parameter of the NMEA0183 BOD (Bearing Origin to Destination) sentence to make it complete. See image below, borrowed from the NMEA2000/NMEA0183 gateway users manual from Maretron.

Of course it would be possible to introduce something like this in the current architecture of NemaStudio, but it definitely would also result in a fairly messy solution as you can imagine.

By adapting the NGW-1 into NemaStudio we achieve a much cleaner solution. All the conversion is neatly done by the NGW-1 and is hidden to the user who just sees occur a nice stream of valid PGN’s on the NMEA2000 bus when sending the appropriate NMEA0183 sentences from NemaStudio.

During tests with the NGW-1 and NemaStudio it was discovered that the default baud rate of the NGW-1 – by factory set to 4800 baud – in many cases turned out to be a severe threshold when used with NemaStudio.

As the NGW-1 is designed to act as a gateway between NMEA0183 devices and the NMEA2000 bus it is expected that there is a limited number of NMEA devices to be handled simultaneously. In normal situations on board a ship this will be the case indeed.

But with NemaStudio you can set up and run a theoretically unlimited number of NMEA0183 devices and multiplex the output of these over one  and the same serial port. It is very tempting and easy to initiate a large number of NMEA devices and feed the output to the NGW-1 port.

With a baud rate of 4800 you will very soon run into the situation that the NGW-1 can’t handle all those messages. Very understandable because 4800 baud means about 450 characters per second. Suppose an average length of 45 characters per NMEA0183 sentence and you can see the problem immediately when you try to transmit more than 10 sentences per second.

NemaStudio offers a few solutions to such a situation. Firstly, you can of course decrease the number of sentences to be send by either reduce the number of simultaneous devices running or by unchecking the sentences you’re not absolutely interested in.

Secondly, you can downgrade the interval time the messages are sent in NemaStudio. Instead of once per second you could set the interval to say 3 seconds for every device, or for devices that require a high update frequency set it to 2 seconds and all others to 10 seconds. Just a few examples, you can experiment with it to achieve an optimum.

As a third option you can of course set a higher baud rate if that is accepted by the receiver.

Now back to the NGW-1. As said, the factory baud rate is set to 4800 and can normally only be changed – either permanent or temporarily – by using a special utility program supplied by Actisense.

But tada! Here is the NemaStudio hack!

In the ports grid on the Communications Settings tab I have introduced a new column: N2000Device. In that column, for each serial port, you can set whether there is a NGW-1 connected to it or not. If you set it to NGW-1 (in the future we are prepared to support other gateways too) the default baud rate changes automatically to 115200 for that port. After that you can eventually change the baud rate to any rate accepted by the NGW-1, but in most situations 115200 will be OK and you can leave it as it is.

NemaStudio will now automatically instruct the NGW-1 to use the set baud rate for the period the port is used. At closing time the NGW-1 is set back to the 4800 default rate.

Introducing this solution will give NemaStudio users the option of connecting to a NMEA2000 network without hassle. Of course one must acquire a NGW-1 from an Actisense dealer for around $150, but licensed users of NemaStudio will find that Sailsoft charges no extra for the latest version of this great software supporting the NGW-1!

The Actisense NGW-1 is supported from NemaStudio Version 1.6 onwards.