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Old 16-04-2018, 00:26   #1
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Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

On an offshore cruising sailboat we find it impossible to have a new Simrad NAC-3 autopilot computer read the wind information from a new Airmar WX220 weather station transducer. Both units are on the N2K backbone. The autopilot is controlled with a new Simrad AP-44 display. The AP-44 operating on the same N2K backbone properly displays the wind data and all of the other data output from the Airmar WX220. Putting the NAC-3 in "wind mode" gives an alarm "AP wind data missing".
Simrad technical support has over the last few months suggested numerous settings and items to check and confirm; none have solved the problem. Simrad is now stumped and states that it does not possess an Airmar WX220 and therefore is unable to investigate further. Airmar outputs wind data PNG 130306 and Simrad NAC-3 looks for wind data PNG 130306.
Anyone have a similar experience or suggestions to resolve the problem?
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Old 16-04-2018, 01:43   #2
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Does the AP see the airmar as a valid source of data for wind? Look in network sources...
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Old 16-04-2018, 03:42   #3
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Matt, the AP-44 "sources" >"true wind">shows Airmar WX220 same for "apparent wind".
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Old 16-04-2018, 09:03   #4
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Is the 220WX on a backbone or a drop?

I see this fairly often on larger boats. The AP computer is usually the farthest device from the masthead sensor and can not see it.

The cause is typically the masthead sensor is on a drop not a backbone. But occasionally if micro cable is used throughout we have to split the system into two networks; Mast network and Boat Network.

An easy check is to plug something like your AP44 into the NMEA cable going to the AP computer. I use an Actisense NGT-1-USB for this.
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Old 16-04-2018, 16:36   #5
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Thanks Keelme. The WX220 is on an N2K drop (about 30 ft.) from the radar mast on the stern of a 43 foot sailboat. The drop connects to the backbone adjacent to the NAC-3 where, in a series of T connectors, the RF 25, AP44, 12vdc, NAC-3, OP-12 are also connected. Proper resistors are on the ends. The only NMEA 0183 input is a Furuno GP-32 GPS via the converter AT1. Precision 9 is also in the backbone.
I had ordered an NGT-1 (USB) and it should arrive today. I'll see what shows up there.
The AP44 input is N2K. Are you indicating there is a way to wire it to the NAC-3 nmea 0183 input?
Thanks
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Old 16-04-2018, 17:04   #6
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

A drop should not be longer than 20 feet. Anything longer than 20 feet should be backbone.

The Airmar cables that are longer than 20' have a built in terminating resistor. If this is a drop that means you have three terminating resistors on the network. If you have three resistors than you are greatly degrading the network performance.

I was using the AP44 as an example of something that would be good to troubleshoot the network. What I meant was unplug the N2k cable going into the AP computer and plug that cable into the AP44 and see if you can see the 220WX from that point on the network.

When you get your NGT-1 get a gender changer for the N2k plug. You will use it a lot.
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Old 16-04-2018, 18:15   #7
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Thanks, Keelme. I have identified the Airmar WX220 drop cable as a WS2-C06 N2K cable that is 6 meters (20ft) long. Airmar specs indicate that only cables longer than this one have the built in resistor. Resistance measured at the NAC-3 is about 59.
The AP-44 is actually physically connected to the backbone further from the NAC-3 than the Airmar connection (if that is relevant?).
I'll find a gender changer.
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Old 17-04-2018, 11:29   #8
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

Well, there goes that idea.

59 is great.

A few things I am thinking:
1. One of the offsets in the AP44 could be causing the problem.
2. Is there a plotter or other device that could be sending a different wind reference?
3. It's always a good idea to make the system as simple as possible when troubleshooting. I would disconnect the OP12 and GP32.
4. Calculate your voltage drop and make sure everything is in spec.
5. Make sure all of your grounds are good. Including N2k Power ground and NAC-3 Grounds.
6. Move the 220WX from drop to trunk with an inline terminator.

From my experience it is always something simple.

Good luck. Let me know if there is anything I can do to help.
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Old 17-04-2018, 14:34   #9
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Re: Simrad NAC-3 Autopilot won't read Airmar WX220 Wind Data

My money is on a NAC-3 bug. There is probably something in the WX220 PGN that although acceptable to the AP44, is causing the NAC-3 to choke. It's too bad Simrad is too lazy to pursue this. Would it really be that hard to for them to go buy a WX220?

I think KeelMe's suggestion is good to strip the network down to something minimal just to test this particular thing. The WX, NAC, and AP44 would be ideal, and show that the AP44 can display the wind data, but the NAC doesn't accept it. Then you have two Simrad products, one of which can display the data and one that doesn't.

Your Actisense trace might give you a clue about what's "different" in the PGN that's causing the NAC to choke.
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