I finally got an opportunity to confirm that my recently installed Raymarine Ray49 DSC-enabled, two-way-NMEA, VHF radio is working correctly. For those just joining us, you can read about my first impressions of the radio itself and my crazy NMEA wiring scheme.
Anyway, once I got it all hooked up a few weeks ago, everything appeared to be working fine. Everything, that is, except NMEA data from the VHF to my Raymarine C-80. This sort of data is pretty infrequent, so I was not able to test that it was working until yesterday. I got some help from Captain Mac Lamay aboard Island Ranger. I sent DSC position requests to Island Ranger to conduct this test.
And it works! When the Ray49 VHF radio receives a vessel position message over DSC, it forwards it (via the AIS) to the chartplotter, which displays a dialogue like this:
At this point, you’ve got three options: place a waypoint, begin navigating toward the coordinates, or clear the message and ignore it.
If I were to see this dialogue box associated with a distress call, here’s what I would do:
I would hit the “Goto Vessel” softkey, and then slow down and listen to the radio for additional information. If I decide that my participation could potentially benefit the outcome, my nav system is already set up to help me get there. If not, I can just “Stop Goto” and proceed on my way.
By the way, I was interested to see just what these DSC NMEA “sentences” look like. There are two associated with each position report, and they begin with CDDSC and CDDSE, respectively. The rest of the messages you see in the buffer are AIS messages.
So after all this, it all really, really works, for which I’m heartily grateful! 
5 responses so far ↓
Roger Bingham // Jun 8, 2008 at 6:40 am
I’m not clear where AIS fits into this – What am I missing?
Tim Flanagan, Managing Editor // Jun 9, 2008 at 7:35 am
AIS is only relevant because the NMEA signals from my DSC VHF radio are going into the SmartRadio AIS unit, there to be aggregated with the AIS data. All that data comes out of the AIS receiver and into my C-80 chartplotter.
All I’m really saying in this post is “it works the way it’s supposed to”, which represents a victory of sorts.
Roger Bingham // Jun 10, 2008 at 1:02 pm
Thanks Tim, but wouldn’t this work just as well (position polling or DSC distress) without any AIS?
Tim Flanagan, Managing Editor // Jun 10, 2008 at 1:35 pm
Heck, it would probably work BETTER!
Which is to say: Yes, AIS is completely tangential to this.
On a Raymarine C-Series multifunction display, though, there is only one NMEA port. I have managed to avoid purchasing a ~$300 NMEA multiplexer so far, by being exceedingly, perhaps unreasonably, “contraptionary” when it comes to my nav system datapaths.
Henry S Reynolds // Sep 7, 2009 at 12:59 pm
Were you able to decode the dsc/dse messages? I have been unable to locate the format of these messages.
v/r
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