DSC Basics

[brazenarticle]

Excellent thread, thanks for getting this started Dockhead.
If I do a resolution this year it will be to utilize more of the functionality of my DSC radio, chartplotter, autopilot and all the other gadgets that I put on the boat.
I actually read the manuals and believe all is properly wired - the radio and chartplotter talk to each other, the autopilot recognizes the chart plotter. Now the weakest link in the chain is me ( all the devices have multiple memories, sadly I just came equipped with one).
I bought the DSC radio (SH 2150 with ram mic at the helm) for the AIS display and the DISTRESS button feature. I also registered an MMSI. THe radio gets GPS from a Garmin chart plotter via NMEA 183. The Garmin is also connected by NMEA2000 to a Raymarine EV100.

On the radio side - if I use individual call directly to another MMSI am I still limited to line of site VHF or does the DSC effectively act as a repeater? Can I call direct call a boat (or some other MMSI) 50 or 100 miles away with DSC?

In an emergency situation does the DSC data show up on the chart plotter? (I think I wired the nmea 183 in/out and ground). Is one button calling for help and marking a MOB on the chart plotter possible? Since I've not used the DSC I've not experienced any DSC data showing on the chart plotter.

Friends have DSC but not AIS transmitters - if they have MMSI info and I set up polling will they show up on the chart plotter, or can I make them show on the chart plotter?

As pointed out earlier in the thread a wikipedia entry, or a detailed article about this will be appreciated!

[brazenarticle]

Originally Posted by brazenarticle

On the radio side - if I use individual call directly to another MMSI am I still limited to line of site VHF or does the DSC effectively act as a repeater? Can I call direct call a boat (or some other MMSI) 50 or 100 miles away with DSC?

Duh! Just realized even if the Digital Selective Calling went beyond the horizon the followup radio answer is still plain old line of sight VHF.

[gamayun]

Originally Posted by brazenarticle

...On the radio side - if I use individual call directly to another MMSI am I still limited to line of site VHF or does the DSC effectively act as a repeater? Can I call direct call a boat (or some other MMSI) 50 or 100 miles away with DSC?

Something that I don't think has been covered in this thread (which is SUPER appreciated, by the way!!), but is implied in this comment, is that a DSC distress message will get passed on to other VHFs like a repeater until it is acknowledged. It is my understanding that the radios of other boats in the vicinity will automatically pass on the DSC alert, even if the skippers don't acknowledge it. I understand these alerts are very loud and persistent, but if you press "ignore," the alarm will stop though the distress function will continue on until answered. I have not used my DSC function at all, but I keep a radio on my PFD for emergency purposes when I'm sailing inshore. Never had to use it and have never tested the function either. Using the DSC for non-emergency purposes is now my goal for 2016...

[Sandero]

So DSC VHFs which are on will act as a repeater and send the distress signal out until "answered"? What does that mean - answered?

[transmitterdan]

Originally Posted by brazenarticle

On the radio side - if I use individual call directly to another MMSI am I still limited to line of site VHF or does the DSC effectively act as a repeater? Can I call direct call a boat (or some other MMSI) 50 or 100 miles away with DSC?

No, if you make a direct MMSI call to another radio it must be within radio range.

[Rusty007]

I am supprised by the number of new radios that don't have NMEA2000 conections. N2K makes networking with the chart plotter simple. It seem that most people do not know how to set up NMEA0183 correctly to make full use of the DSC features.

N2K is so easy to set up and on some VHF / Chart plotter combos adds extra functionality the 0183 can't provide.

[Rusty007]

Originally Posted by Sandero

So DSC VHFs which are on will act as a repeater and send the distress signal out until "answered"? What does that mean - answered?

Answered by a coast guard land based station or similar.

[gamayun]

Originally Posted by Rusty007

Answered by a coast guard land based station or similar.

Well, this brings up an interesting question to me and that is: What if a boater who receives a DSC alert some ways offshore determines that he is really close by, so he acknowledges the distress, and then goes over to help -- say pluck an MOB out of the water. Everyone is shaken up, cold and wet, but fine; now what happens? Would a CG helicopter fly over to check things out if they did not get an answer, particularly if the boaters are out of VHF range?

[cal40john]

Originally Posted by gamayun

Something that I don't think has been covered in this thread (which is SUPER appreciated, by the way!!), but is implied in this comment, is that a DSC distress message will get passed on to other VHFs like a repeater until it is acknowledged. It is my understanding that the radios of other boats in the vicinity will automatically pass on the DSC alert, even if the skippers don't acknowledge it. I understand these alerts are very loud and persistent, but if you press "ignore," the alarm will stop though the distress function will continue on until answered. I have not used my DSC function at all, but I keep a radio on my PFD for emergency purposes when I'm sailing inshore. Never had to use it and have never tested the function either. Using the DSC for non-emergency purposes is now my goal for 2016...

The forwarding of messages does not happen. It was in the plan and the USCG had a youtube video that said it does that didn't get removed for a long time, but I believe it was never implemented. There's a thread somewhere on cruisersforum with details. I think the problem is a cascade effect especially with HF.

[Rusty007]

Originally Posted by gamayun

Well, this brings up an interesting question to me and that is: What if a boater who receives a DSC alert some ways offshore determines that he is really close by, so he acknowledges the distress, and then goes over to help -- say pluck an MOB out of the water. Everyone is shaken up, cold and wet, but fine; now what happens? Would a CG helicopter fly over to check things out if they did not get an answer, particularly if the boaters are out of VHF range?

As another boater you can acknowledge a distress call and assist. The vessel that send the message can then cancel the call once the danger is over.

You can not stop the call being repated by the sending vessel. Only the coast guard or the sending vessel can stop the repeating message. If you acknowledge the call it will stop repeating on your radio only.

[Sandero]

What would happen for instance if a vessel sent out a DSC distress call... and then their radio failed for whatever reason. Would the CG follow up or assume it was a mistake? If the called the distressed vessel their call would and could not be answered. I would assume that they would still send out a boat or plane to the lat lon of the call. Yes or no?

Curious... how loud are the alarm tones? Can they be tested and the volume adjusted?

This sounds as if CG is trying to save 16 for emergency only... and the DSC allows a person to alert and call a specific vessel via DSC "signal" using their MMSI. I suppose the difference would be that the called vessel would hear an alarm tone instead of being hailed?

[Rusty007]

Originally Posted by Sandero

What would happen for instance if a vessel sent out a DSC distress call... and then their radio failed for whatever reason. Would the CG follow up or assume it was a mistake? If the called the distressed vessel their call would and could not be answered. I would assume that they would still send out a boat or plane to the lat lon of the call. Yes or no?

The correct procedure for a distress call should be to triger the DSC alarm and follow up with the normal voice distress mesage. If a vessel makes a call then goes silent I would hope someone comes to check.

Originally Posted by Sandero

Curious... how loud are the alarm tones? Can they be tested and the volume adjusted?

The Alarms are loud and I don't think there is a volume contorl

Originally Posted by Sandero

This sounds as if CG is trying to save 16 for emergency only... and the DSC allows a person to alert and call a specific vessel via DSC "signal" using their MMSI. I suppose the difference would be that the called vessel would hear an alarm tone instead of being hailed?

Correct.

[transmitterdan]

If a DSC distress call is made by pushing the red button but never any voice contact and the distress message self terminates then probably no SAR will be triggered. The shore side contact may be contacted. If the call repeats forever I am not sure what the USCG would do with that. They may investigate but probably not going to launch a helo.

DSC is not a replacement for EPIRB or PLB. DSC is an improvement in sending Mayday messages because it includes coordinates and vessel identification. But it still requires voice comms to establish the nature of the emergency.

[Rustic Charm]

Great thread. I just want to emphasize that given this is an international forum, some of the answers will need to be contextualized to different countries.

IN Australia for instance - Our search and rescue authorities, co-ordinated by AMSA 'will' respond to all calls for assistance. The only assumption they will make is that someone needs assistance and they will send out a helo, plane or near vessel to investigate.

Again in Australia, most shore stations don't have DSC capabilities, so I'm told. So the DSC red button on the radio will be relying on another vessel to pick up the electronic distress and alert authorities.

My understanding of DSC is that DSC is semi automatic. It's particularly great when you can't be heard over the radio due to distance or noise, but the digital data can be, given it's not voice.

[Rustic Charm]

Originally Posted by Sandero

What would happen for instance if a vessel sent out a DSC distress call... and then their radio failed for whatever reason. Would the CG follow up or assume it was a mistake? If the called the distressed vessel their call would and could not be answered. I would assume that they would still send out a boat or plane to the lat lon of the call. Yes or no?

Curious... how loud are the alarm tones? Can they be tested and the volume adjusted?

This sounds as if CG is trying to save 16 for emergency only... and the DSC allows a person to alert and call a specific vessel via DSC "signal" using their MMSI. I suppose the difference would be that the called vessel would hear an alarm tone instead of being hailed?

Definitely would do in Australia's Search and Rescue zone. And yes, I would imagine the CG are trying to save channel 16 for emergencies only.. Given that is what it is for and for calling in the first place.