EM-TRAK A100 Class A AIS for $1K at WM?!?

[ronstory]

Ok, sometimes you stumble across a good deal (I think). I have been shopping for an AIS transponder and have been watching the Class B with SOTDMA begin to enter the market. I was hoping for a Black Friday deal in a few weeks, but then I was trolling through West Marine trying to find a use for $50 off coupon on $300 or more... and found this:

https://www.westmarine.com/buy/em-tr...44?recordNum=5

It's an older Class A but searching around at places like Mill Tech... it about 30% less. Add-in the $50 coupon (ends today) and I can full Class A for about $300-400 more than the new Class B SOTDMA devices.

Now this unit only does NMEA-0183, but I can use my raymarine chartplotter as bridge to the N2K network.

So does anyone have one? Or has seen first hand the advantage of Class A on a medium speed sailboat?

[Paul L]

That's pretty cheap for a Class A unit. You don't get some of the nice Vesper features, but you get the power output of Class A. You would be more likely to be seen, and in some cases paid better attention to as they try and figure out what this little spec is broadcast g Class A.

[ronstory]

Yes, I like the SW interfaces and features of the Vesper, but they don't support SOTDMA in Class B.

I just finished the A100 manual and the Class A has a few more features like the voyage data menu where you scan set the state of the boat, destination, ETA etc. From the manual:

Navigational status - select the most appropriate navigational status for your vessel from the list.

Under way using engine
At anchor
Not under command
Restricted manoeuvrability
Constrained by her draught
Moored
Aground
Engaged in fishing
Under way sailing
Not defined (default)

[Paul L]

Originally Posted by ronstory

Yes, I like the SW interfaces and features of the Vesper, but they don't support SOTDMA in Class B.

Not yet.

I just finished the A100 manual and the Class A has a few more features like the voyage data menu where you scan set the state of the boat, destination, ETA etc. From the manual:

Navigational status - select the most appropriate navigational status for your vessel from the list.

Under way using engine
At anchor
Not under command
Restricted manoeuvrability
Constrained by her draught
Moored
Aground
Engaged in fishing
Under way sailing
Not defined (default)

Yep, that is all required for Class A. Those are the items that are so often broadcast in error.

[tanglewood]

That same device, made by SRT, is re-badged by a number of different vendors. I had the Comnav version, but they are all identical. It's a good device, tough perhaps a bit dated. But Class A functionality is pretty strictly defined and regulated, like having 0183 interfaces and all the features you found. I was very pleased with mine and will buy the same again unless there is a newer version in a year when I'm ready to buy.

[ronstory]

Paul & Tanglewood--

Thank-you for the pointer. Since WM has a awesome return policy I just ordered it. It was $949.99 with the coupon discount and I'll pick it up the in store next week.

Paul... also our boat is now feeling a bit self-conscious after being refereed to as "this little spec" and may start to sulk. If it doesn't start the next time I'm in Gig Harbor, I'm blaming you. ;^)

[tanglewood]

Just FYI, class A is very stringent about proper input data. Heading (and I think true heading), ROT, and position are required inputs or it will produce errors. There may be others, but I can’t recall. True heading can be a trick to produce without a sat compass, or of course a gyro.

[ronstory]

Thanks for the heads-up. I have a Raymarine EV-1 sensor core, so I have a true heading indicator. I'll need to dig through the A100 manual again to see if they specify PGNs.

[ronstory]

Ok, went though the A100 manual again since I didn't remember seeing any PGNs. I got it right the first time... there are none in the doc. Drat. The doc does reference a spec IEC 61993-2 it is looks like I need the data from Annex B.

Annex B for the curious is the "Annex B (informative) New IEC 61162-1 sentences due to AIS"... but I don't feel like paying "CHF 320" in Swiss francs (about the same in USD) to look up some !AIVDM sentences.

Does anyone have a unofficial reference for the !AIVDN sentences needed for a Class A AIS? Perhaps a NMEA 0183 network dump?

Oh... I severely dislike closed specs.

[tanglewood]

IEC 61162-1 is the NMEA-1083 spec for 4800bd operation
IEC 61162-2 is the NMEA-0183 spec for 34.8kbd operation for AIS output.


Your new AIS is 100% NMEA 0183. There is no N2K anywhere since it's not an IMO approved communications standard. There is an IEC spec for it, IEC 61162-3, but it's not approved for use on IMO boats.


Class B AIS can operate without the aid of external sensors. That's why they all include their own GPS. This is to make installation easier and more fool proof. They can be used as output only devices when connected to other nav equipment.


Class A AIS is somewhat the opposite. It still includes it's own GPS, but it is strictly a backup. Class A must be connected to the ships sensors, and those are the primary sensors used by the AIS. That data must be present or the AIS will generate an alarm. It will continue to work using it's own GPS, but it will be in a continuous alarmed state.


Your SeaTalkNG network is all N2K, as I recall SeaTalk, so you will have to do a bunch of converting. If your MFD has one or more 0183 ports, you might be able to use those.


AIS data coming out of the A100 will be at 34.8kbd, and presumably needs to be converted to N2K/Seatalk to display on your MFD. Or maybe you have an 0183 port you can use.


The AIS also needs to receive instrument data. Your EV-1 may or may not be adequate. First, you will have to convert to 0183. Second, I'm pretty sure you need true heading, not magnetic. I might be confusing this with an IMO radar as to which requires true heading, but looking at the manual it says it wants HDT which is true heading. Now just because you can display things in magnetic or true on your MFD doesn't mean true heading is on your network or available from any instrument. Display devices derive true heading from magnetic heading and variation coming either from your GPS or from your chart plotter itself.


When I installed mine, I wanted to use my N2K rate compass and N2K GPS as backup data sources for the AIS, and it was very difficult to get HDT. Converters only generate HDT if there is a true heading source on the N2K side, and the only thing I know of that produces true heading is a sat compass.


I did find two rate compasses that, if set up correctly, can produce HDT on 0183. One is the Maretron SSC200/300. In addition to it's N2K output, it also has an 0183 interface. If you feed the SSC with Variation either via N2K or 0183, it can be set up to produce HDT on the 0183 interface. But that means you need to have an always-on source of Variation. A mushroom GPS would be an obvious source since it's always on, but not all produce Variation. Another source of Variation can be an MFD, but there are likely times when you want that turned off, and if you turn it off, no more HDT and the AIS will alarm. The other rate compass that can do something similar is the Furuno PG500/700, though I don't recall if it's one or both of them.


As I mentioned in my previous note, you also need to send ROT, and some collection of GPS position, SOG, and COG to the AIS. It will alarm if you don't, or if they go away at any time.


Another consideration is the data rate of 0183. If you install a converter to move data from N2K to 0183, assuming all the requisite data is available, you can quickly overwhelm the capacity of a 4800bd 0183 link. A fast heading source (HDT, ROT @10hz), or a fast GPS sources (GLL, SOG, COG @10hz) is about all a link can handle. So I highly recommend running your 0183 links at 34.8kbd. It just makes the problem go away.


And as you consider converters, this article might be helpful Adventures of Tanglewood: NMEA 2000 to NMEA 0183 converter challenges I found a lot of frustrations with N2K to 0183 converters, all prompted by trying to get N2K data fed to an IMO radar and IMO AIS.


My conclusion was that in the absence of a sat compass, which most people don't have, it's actually quite difficult to interface to a Class A AIS, and requires a lot of extra equipment. You are probably looking at a minimum of 2 converters, and maybe a rate compass. Combined those will probably cost as much as you paid for the AIS.


I'll be real interested to hear how you make out, and how you get everything to work. Maybe Ray has some tricks up their sleeves, or maybe converters have evolved....

[tanglewood]

Originally Posted by ronstory

Thanks for the heads-up. I have a Raymarine EV-1 sensor core, so I have a true heading indicator. I'll need to dig through the A100 manual again to see if they specify PGNs.

You probably need an analyzer of some sort to tell whether the EV-1 sends true heading, but I'll bet you a six-pack that it doesn't. On N2K it's the same PGN, but there is an indicator in the PGN telling whether it's magnetic or true.


And there are no PGNs listed in the A100 manual because it's exclusively 0183.

[mickand]

I don't begin to understand the aforementioned technical comments. However I installed an A100 two+ years ago. The unit's own screen lists all targets with distance and heading info.
All targets are overlaid on my Simrad NSS chartplotter and radar screens including safe/dangerous dialogue boxes on radar screen.
I use target extension lines and they show as accurate in heading .
I have traveled extensively on all the major US rivers and would not be without it
The unit updates my position every 5 seconds so towboats always see me in real time.

[ronstory]

Mickand--

Just to be clear, you just connected the A100 to the NMEA-0183 wires on the NSS chartplotter? It looks like did the NSS has similar functionality to my Ray C97 in that it will bridge N2K to the 0183 network. Did you get any alarms from the A100 during setup or require any additional HW?

[ronstory]

Wait a moment... I see perhaps a bit of hope.

I was digging around the raymarine site and found out they have a Class A AIS unit as well. It's called the AIS950 ooks identical to the A100... right down to the no N2K port and only 0183 interface.

AIS950 Spec. US

[tanglewood]

Originally Posted by ronstory

Wait a moment... I see perhaps a bit of hope.

I was digging around the raymarine site and found out they have a Class A AIS unit as well. It's called the AIS950 ooks identical to the A100... right down to the no N2K port and only 0183 interface.

AIS950 Spec. US

Yes, another example of the same unit sold under different brands. Furuno makes their own Class A device, and so does Amec, but I think all others are this SRT device. The manuals are pretty much word for word identical.


Please keep us posted on the installation. It may be that you can just ignore the input sensor alarms, but I wasn't willing to do that. I'm real interested to know what other tricks might be available for installing Class A in a recreational boat, in particular one that doesn't have a sat compass.