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Old 01-10-2015, 05:22 PM   #1
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Problem with multiple AIS devices on N2K

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Originally Posted by CaptTom View Post
I've been looking at these too. I'd like to hear more about why you didn't keep this one.

I like the display of AIS data and other features, but I have an AIS transceiver on the NMEA 2000 bus already, and wondered what would happen if I added another receiver like this.

Ideally, I'd want this radio, with the AIS target display, but without the receiver.
This is indeed why I changed my VHF to a non-AIS model. Here are the details, and it's another example of how marine electronics vendors are doing a very poor job implementing N2K and creating a bad name for it.

I have an AIS transponder on my boat made by Simrad (NAIS400). When selecting VHFs, I figured I'd pick a model with integrated AIS so I would have a backup receiver if the main transponder ever failed. This is consistent with pretty much every other critical part of my nav system - everything has a backup so I can keep going if any critical component fails. This did not work at all with AIS, and surfaced a number of bugs and/or design oversights in multiple products. Here's what I found:

1) N2K has a mandatory feature called a Device Instance. It's just a number that you assign to devices to distinguish them when they are otherwise sending the same info. If, for example, you have two GPSs, they should be assigned different Device Instance numbers, say 1 and 2. Then, you can tell your chart plotter to use GPS #1, and it knows which one to listen to. If your GPSs are in sufficiently different locations on your boat, they will be reporting different positions. A chart plotter that can't tell them apart is going to get confused because depending on which it hears at any given time, your boat will seem to be jumping around. Plus, if GPS #1 fails, you can tell the plotter to switch to GPS #2. It's a really useful and important aspect of N2K, but most vendors manage to screw it up in one way or another. After this pre-amble of Device Instance info, the NAIS400 does not let you change the device instance. Even though it's a NMEA 2000 Certified device, it violates the spec in this fundamental way. Step one for having multiple AIS receivers on N2K is to be able to distinguish them from one another, and so far we are not off to a good start.

2) I'll skip over my attempt to use Simrad RS35 VHFs, three of which were returned to the manufacturer stone dead after less than 24hrs of operation.

3) The Simrad VHFs were replaced by ICOM M506 AIS models. These were unable to properly discover the available GPSs on the N2K network, let alone select which to use for position for DSC. A call with ICOM support, who were very good, by the way, revealed that I needed V1.002 firmware, so I got the VHFs updated. Now they were able to discover and select a GPS on the network. So that problem was solved.

4) Now, with 3 AIS receivers on N2K, I needed a way to tell my chart plotter and radar which one to use. The usual way to do that is to assign Device Instance numbers to the three AIS devices, then go to the listening devices and tell each which AIS to use. Really clever listening devices can be given a priority list of sources, and will always pick the highest priority device that's available, and automatically work down the lists in the event of failures. Now recall that the Device Instance can't be changed in the NAIS400, but being the clever sort that I am, I left it at zero and changed the VHFs to 1 and 2. But now I discovered that none of the listening devices have the ability to select which AIS to use. And I can't tell whether they are listening to all of them and processing three copies of every position report, or if they are somehow picking one of the three to listen to. It's anyone's guess. The good news is that nothing seemed to blow up, so I figured I'd just let it go. Wrong.

5) With AIS there is the whole issue of your own ship's position report, and how to filter it out so you don't always appear to be crashing into yourself. As best I can tell there is no standard or convention for who does the filtering. It appears that the NAIS400 transceiver filters and does not issue your own ships report on N2K, but the VHF AIS receivers don't filter it and instead report your own position on N2K. Coastal Explorer can't filter my own AIS reports because it doesn't know my MMSI number, so it starts complaining that I'm about to crash into myself any time one of the VHFs is turned on. The Simrad chart plotter appears to filter the reports sent by the VHFs because it does not report imminent death, and it does know my MMSI number. Undaunted by this, I figured I'd just disable the AIS reports in the VHFs. No-go. There is no such feature.

6) Because there is no means to turn off AIS reports from the various receivers, ship's position reports come out in duplicate or triplicate, resulting in a lot of excess traffic on the bus. And AIS reports are long and frequent, so they do tend to gum up the works.

It would appear that in specifying how AIS is carried over N2K, the standards folks failed to consider more than a single device, and failed to be clear on what filtering of own-ships reports is required and where. I think the crap is really going to hit the fan as these AIS-equipped VHFs start finding there way into everybody's boat, and pretty soon you have more than one whether you want it or not.

I have reported all this to NMEA, ICOM, and Simrad. I would urge anyone buying product to check with your preferred vendor and ask them whether the product supports Device Instancing (they probably won't know what you are talking about), and whether the AIS repots on N2K can be disabled. If you get the wrong answers, tell the vendor why you are not buying their product.

In the mean time, I'd suggest only one AIS receiver on N2K.
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Old 01-10-2015, 06:29 PM   #2
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Hello Twistedtree

Nice post you got there.
In my case; I have a full Garmin system including two stations with Radar/Chart/Depth. I NEED to add an AIS due to the vast traffic on Brazilian coast and I was thinking about the ICOM class B. Having in mind that my system is already there and I also have a pair of Garmin VHF's would you recommend to add a Garmin product like the 600 AIS Transceiver for example?

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Old 01-10-2015, 06:34 PM   #3
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... By the way. Th idea of the ICOM was to have a stand alone instrument for AIS...
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Old 01-10-2015, 07:08 PM   #4
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Hello Twistedtree

Nice post you got there.
In my case; I have a full Garmin system including two stations with Radar/Chart/Depth. I NEED to add an AIS due to the vast traffic on Brazilian coast and I was thinking about the ICOM class B. Having in mind that my system is already there and I also have a pair of Garmin VHF's would you recommend to add a Garmin product like the 600 AIS Transceiver for example?

Thank you

Portuguese

Are any of your VHF's right now AIS receivers?

The AIS600 would work great with your garmin equipment. Like Twisted said you just can't have two sources of AIS data on the N2K network.
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Old 01-10-2015, 07:12 PM   #5
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What happens if you just disconnect the radios from the nmea 2000 network? You could always reconnect one if you needed a back up AIS.

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Old 01-10-2015, 07:15 PM   #6
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What happens if you just disconnect the radios from the nmea 2000 network? You could always reconnect one if you needed a back up AIS.

Ted

But then you don't have position on the radio, you would have to connect the radio to 0183 which totally defeats the purpose of a N2k VHF.
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Old 01-10-2015, 07:28 PM   #7
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I don't have experience with either of those products. Are they both N2K connected, or do they connect via 0183 or Ethernet? I think in general N2K works fine when you don't have duplicate, redundant devices. But as soon as you have two or more of something, much of it starts to come unglued.
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Old 01-10-2015, 07:32 PM   #8
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What happens if you just disconnect the radios from the nmea 2000 network? You could always reconnect one if you needed a back up AIS.

Ted
You could do that, but they get their GPS position off the N2K network so DSC wouldn't work. You could bring in the GPS info via 0183, but then why have N2K?
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Old 01-10-2015, 07:33 PM   #9
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But then you don't have position on the radio, you would have to connect the radio to 0183 which totally defeats the purpose of a N2k VHF.
Wow, couldn't have said it better myself..... I should have read your post first. Pretty funny, eh?
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Old 01-10-2015, 07:43 PM   #10
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Wow, couldn't have said it better myself..... I should have read your post first. Pretty funny, eh?

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Old 01-10-2015, 07:48 PM   #11
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You could do that, but they get their GPS position off the N2K network so DSC wouldn't work. You could bring in the GPS info via 0183, but then why have N2K?
This is definitely a screw up on ICOMs part. I have 2 AISs (not ICOM) one on each boat. Both give you the option to turn the transmit portion off (which would solve your problem). I've used ICOM radios exclusively for 30 years starting with the M100s. This is the first thing that I can think of that they really missed the boat on.

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Old 01-10-2015, 07:49 PM   #12
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Very good description of the issue.

I think the same concept probably applies to NMEA 0183 systems as well.

We have a furuno AIS on the Furuno Ethernet network.

If we put in a radio that has a AIS receiver, and we connect its NEMA 0183 to the chart plotter we might get a similar problem.

The chart plotter is not aware of our MSSI so it'll receive a AIS message from ourselves and think we're going to crash
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Old 01-10-2015, 08:34 PM   #13
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This is definitely a screw up on ICOMs part. I have 2 AISs (not ICOM) one on each boat. Both give you the option to turn the transmit portion off (which would solve your problem). I've used ICOM radios exclusively for 30 years starting with the M100s. This is the first thing that I can think of that they really missed the boat on.

Ted
I don't disagree in any way. And Icom isn't alone. Each vendor I've dealt with has their own little package of surprises and oversights.
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Old 01-10-2015, 08:37 PM   #14
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Very good description of the issue.

I think the same concept probably applies to NMEA 0183 systems as well.

We have a furuno AIS on the Furuno Ethernet network.

If we put in a radio that has a AIS receiver, and we connect its NEMA 0183 to the chart plotter we might get a similar problem.

The chart plotter is not aware of our MSSI so it'll receive a AIS message from ourselves and think we're going to crash
True, but you can probably turn that port on/off on the MFD.
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Old 01-11-2015, 04:31 PM   #15
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I notice the M506 has an N2K option that comes without an AIS receiver.

Does anyone know if this one has the ability to DISPLAY the AIS data from the N2K network? That might be the only solution. I only wish iCom had a wireless mic option.
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Old 01-11-2015, 06:37 PM   #16
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I notice the M506 has an N2K option that comes without an AIS receiver.

Does anyone know if this one has the ability to DISPLAY the AIS data from the N2K network? That might be the only solution. I only wish iCom had a wireless mic option.
That's the model M506 that I have - N2K but no AIS. I just tried it and the answer is Yes, it will display targets that are put in the N2K network by another AIS transceiver/receiver, in this case a Simrad NAIS400.

But if you want to display AIS targets, I think a VHF is about the worst possible device to do it on. The screen is the size of a postage stamp, and the user interface about as bad as they get. Your chart plotter and/or Radar I think are the best places to display targets.
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Old 01-11-2015, 08:46 PM   #17
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That's the model M506 that I have - N2K but no AIS. I just tried it and the answer is Yes, it will display targets that are put in the N2K network by another AIS transceiver/receiver, in this case a Simrad NAIS400.

But if you want to display AIS targets, I think a VHF is about the worst possible device to do it on. The screen is the size of a postage stamp, and the user interface about as bad as they get. Your chart plotter and/or Radar I think are the best places to display targets.
Agreed, the AIS display on the chartplotter is the primary display.

But it seems that there would be some benefit to having a dedicated AIS display, however small. The vessel icons sometimes get lost in the clutter on the chartplotter.

Also, I thought the VHF radios had some ability to highlight a target and display information or make a call to them.

Finally, the VHF would provide a backup AIS display in case the chartplotter fails.
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Old 01-11-2015, 08:50 PM   #18
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I have Simrad NSO evo2, Simrad RS35 and RS90 VHF radios, and Sitex AIS all on the N2K network, without problems at this point (at least on the RS35 failure and multiple AIS).
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Old 01-11-2015, 08:53 PM   #19
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I have Simrad NSO evo2, Simrad RS35 and RS90 VHF radios, and Sitex AIS all on the N2K network, without problems at this point (at least on the RS35 failure and multiple AIS).

The problems are probably there, you just don't know it yet....
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Old 01-11-2015, 09:03 PM   #20
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Oliver,
Perhaps but the RS35 has worked since it was installed in May. I did have a problem with the weather alerts, but got that figured out.
The NSO evo2 has an option to exclude from reporting my own MMSI number.
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