Connecting NMEA input to Navman 8084 Chartplotter

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

Getting Seatalk, Navbus and NMEA to talk…

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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Raymarine ST4000+ Autopilot: Installation

When I acquired Sunny Spells, she had a Raymarine ST4000+ wheel pilot installed. The autopilot was only about 18 months old, as evidenced by the invoice which was still on the boat. The autopilot was an important selling point when I bought the boat, because I knew that I would be sailing short-handed or solo a lot of the time.

Unfortunately, I had to resign myself to the fact that the Autopilot was a fair-weather sailor only! It would helm fine to windward on a nice day (i.e. winds in the 10 to 15 knot range, flat seas…), exactly the conditions in which I could trim her to sail hands-off anyway! So what good is that then, you may well ask?

Well, in short, none at all…

To my frustration, the autopilot would snake all over the place when going downwind, often disconnecting because it couldn’t keep the heading within 40 degrees. Start the motor, and the heading on the fluxgate compass would change by up to 30 degrees, and changing the throttle setting would have similar effects.

I assumed that this was the sort of performance available from an entry-level autopilot…

During the refit that followed our dismasting, I decided to fix a couple of things that might affect the performance of the autopilot:

  • the rudder angle sensor was never fitted, but it was on the boat, complete with all fittings;
  • the fluxgate compass was originally installed about 12 inches from the alternator/engine… Need I say more?
  • the power supply to the Autopilot was an unprotected connection direct to the house bus, used un-tinned wire and was connected with those screw terminals used in home wiring. Corrosion everywhere…

The re-wiring of the electrical system took care of the power supply side of things.

The fluxgate compass was moved to one of the intermediate bulkheads, under a bunk and next to the flexible water tank. This location was close to the keel (i.e. a stable location with the least movement but accurate representation of the boat’s heading) and far away from potential interference (engine, alternator, vhf, loudspeakers…).

The rudder angle sensor was installed, but I could not get it to work. A quick check with the multimeter indicated that it was dead as the proverbial.

I assumed the sensor had to be a simple potentiometer, but none of the wire pairs would measure any resistance on the multimeter. I took a deep breath and opened the unit: two wires broken off at the solder connections to the potentiometer! Nothing a bit of solder wouldn’t fix…

After re-connection, the autopilot still wouldn’t show rudder angle!

Out with the user manual…

After a lot of trial and error, mostly error(!), in desperation, I told the autopilot that it was now a “tiller-pilot”, not a “wheel-pilot” (the tiller-pilot can’t accept rudder angle sensor input…). Lo and behold, as soon as I saved that setting, the rudder angle appeared on the display! I restored the setting to “wheel-pilot” and the rudder angle was still displayed!

Now for sea trials…

The sea trials exceeded my wildest expectations! The heading info from the fluxgate compass is now stable (no interference when running the engine) and, most importantly, the autopilot now does a great job of steering the boat under all conditions: upwind, downwind, reaching, running. I’m also impressed with how it auto-trims so that it keeps course better and better the longer it is engaged. Moral of the story:

  • autopilots need a high capacity, clean power supply;
  • choose the installation location for the fluxgate compass very carefully – this is the most important input the autopilot has; and
  • install the rudder angle sensor, even if it is a pig of a job (not easy to get to the rudder post…).

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