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Navbus/NMEA and Displaying Wind Data

Mystery solved…

After a lot of correspondence, telephone calls and hours in the boat, in front of the laptop, decoding NMEA0183 sentences (did I really need to know all this stuff??), the mystery is finally solved…

It appears that the chartplotter firmware is the culprit. If Navbus is enabled on the chartplotter, it will only accept wind data from Navbus, not the NMEA0183 input. Disable Navbus, and the wind data is displayed!

It seems like a quick fix, but it comes at a price. The biggest issue is that DSC capability (i.e. automatic communication with the VHF to receive and transmit DSC messages) is lost. Also, the barometric pressure and air temperature data sensed by the VHF is now not available at the helm… Navman’s John Dusting said that he would request a firmware update to solve this issue, but it could be a while…

When I got around to installing the AIS receiver in Sunny Spells, I had a bit of a frustrating time working out how to connect to the NMEA input of the Navman 8084 (similar to Navman 8084, Northstar M84 and Northstar M120). The handbook was no help at all…

A quick call to Navman confirmed what I had found elsewhere on the internet:

  • The NMEA 0183 input is on the white “Fuel/Nav” input on the Navman/Northstar unit.
  • You need one of the Navman/Northstar extension cables with an LT8 plug on one end and bare wires on the other. AA002412 is one of the part numbers but there are several others that would work (different cable lengths have different part numbers…). Your friendly Navman/Northstar dealer can help you order the right cable.
  • The WHITE and BLACK wires on the extension cable are used for the NMEA 0183 input. Black (you guessed it…) is the NMEA negative (earth) and white is the NMEA positive.

Navman 8084/8120 and Northstar M84/M8120 rear connections

Remember that the chartplotter will look for some inputs on the NavBus input if that option has been activated. For example, if NavBus is turned on, the chartplotter will NOT look for wind data on the NMEA input even if there is no wind data on the NavBus input – very annoying! The NMEA input automatically selects the high speed option (38400 baud) if a high speed data stream (such as AIS or a multiplexer with a 38400 baud output) is connected.

Getting Navbus, Seatalk and NMEA to talk

Wout at Brookhouse replied to my e-mail today. (Thanks Wout for your prompt reply and the USB driver). Of course, I remembered this morning that I had printed out the user manual for the MUX and had bound it nicely, with a pocket for the CD, in the back…

The MUX is now connected to the PC via USB. All operating at 38,400 baud as the AIS is also connected. Digiboat’s Software-on-Board shows all wind data present and correct (see screenshot). So where’s the problem?

Looks like I’ll have to go to Navman for this one…

Wind data displayed on SoB

Here’s a mystery…

The navigation electronics on Sunny Spells is a mix of Navman and Raymarine equipment. Navman has its own, proprietary communication protocol called ‘NAVBUS’. The Raymarine equipment uses ‘SeaTalk’. On top of this, there is the AIS receiver which transmits data in NMEA0183, but at 38,400bps (bits per second), while most NMEA equipment communicate at the slower data rate of 4,800bps. Sounds like a nightmare to get them all to talk?

Yes and no…

The core of the communications backbone is the Brookhouse multiplexer (MUX) with SeaTalk and AIS options and USB output. When I installed the MUX, I wasn’t expecting immediate success; imagine my delight when the whole system aapeared to work straight out of the box – no modification required!

However, I have started playing around on the chartplotter, and all is not as it seemed…

The data from the wind instrument is not available on the plotter or the Repeat 3100 (both on Navbus). I’m assuming it’s a Seatalk to NMEA conversion issue, but I haven’t been able to investigate as I can’t get the laptop connected. Unfortunately I seem to have mislaid the CD with the USB-Serial driver for the Mux, so I can’t get the laptop connection sorted – aaargh! I’d love to have the wind info on the plotter (which is at the helm) as the crew are forever blocking my view of the wind instrument!

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