DSC question: Distress Relay Ack?

[tobnpr]

Back on July 3rd I hear an alarm sounding from the boat that I had not heard before, turns out it was my VHF (the electronics were on) and I have this on the display:

I had no idea there were so many types of DSC calls; the manual mentions Distress Relay and Distress Relay Acknowledgement but offers no explanation of what they mean.

I can't find any info online including the USCG site. Anyone know what this means? I didn't respond to the call because I didn't have a clue...

 

[Nehalennia]

The USCG can relay a call they have received that may have been slighty out of your range or poor signal. For instance if the system was working properly and you and the boat in distress have their equipment connected properly to your respective GPSs, you could see the MMSI # you display including the coordinates. With that info you can see if you're close enough to render assistance. With the Garmin I have installed it will actually place an Icon of that boat on the screen with options to "navigate to". This way, I can see not only where he is but how quickly I could get there. Depending on location you may be close but the signal wasn't strong enough from the distressed vessel to reach you, but the USCGs more powerful signal can relay it to boats in that area.

 

[sprink56]

Hey Mike...it makes me wonder if that acknowledgement is in response to a transmission from your radio:huh:

Do those lat and lon numbers look familiar? I'm as curious as you are on this deal.

I like the new sig pic.:thumbsup:

 

[fc3]

Interesting. Not all recreational VHFs will receive and display this. You must have a class-D receiver. Intuitively, one may think that automatically relaying a distress call from a vessel that might be out of range via other vessels to the Coast Guard would be a good thing. However due to latency and propagation delays, one distress call relayed from vessel to vessel could result in dozens or even hundreds of relayed messages. Therefore distress calls are not automatically relayed. A message is displayed so that it can be verbally relayed via channel 16.

Best regards,
Frank

 

[Nehalennia]

Here's some good info about this.
http://www.navcen.uscg.gov/marcomms/gmdss/dsc.htm

 

[tobnpr]

So I think I get part of the equation...
A digital distress call broadcast on Ch 70- assume it is broadcast at the same 25w and therefore has the same (line-of-sight) range, around 6-8 miles or so boat-to-boat depending on antenna heights. So, the USCG relays the call so that boats outside of that range, but still close enough to assist can do so?

Makes sense, but what's the diff between "distress relay" and "distress relay acknowledgement"?

The capabilities, and apparently the complexities, of this DSC stuff amaze me. Gone are the days of just plugging "it" in and using it... I was frustrated at the time because I really didn't know what I should have done. I was at the dock and not really in a position to assist, but if this were to happen offshore it would be nice to know exactly what it means and what I should do...

Frank; yes, it's Class "D" (Uniden 625C)
Todd; some day I'll get around to adding a multiplexer so I can send the DSC info from the radio to the plotters. The RM plotters only have one NMEA input (sucks...).