DSC (Digital Selective Calling) Explanation

[ranger58sb]

Originally Posted by El Pinguino

I don't often just have a chat with people on VHF, the last time was either November or December 2008. However a major impediment to making a ship to ship call by DSC VHF would be knowing the MMSI of your friend's yacht. Esp as in an anchorage the simplest source of that knowledge - his AIS transmission - is probably not available as his AIS transceiver is most likely switched off if indeed he has one.

OK, offshore if you want to speak to a big ship bridge you will have their MMSI if you have AIS.

Just piggy-backing on this...

We don't chat often, either. But if we were inclined to hail another friend's boat, we'd likely already know the boat's name... and it's faster to just voice hail on 16 (or 9 is better, around here) than it is to key in their MMSI to hail their radio via a DSC call. If I were to even know their MMSI.

As for ship transmitting at AIS signal, that would give me the MMSI... but it also gives me the ship's name... so it's faster to voice hail on 13 than it would be to fool around entering an MMSI into our radio.

Might be different if we were part of a group of boats who feel the need to yak at each other incessantly... so MMSIs could be entered in advance... but we're not so we don't.

I thought about the potential for hailing marinas, but our radio uses a pre-set "switch-to" channel (69) for non-distress calls, and in addition to the pain of entering marina MMSIs, the marinas usually already have their own working channel sorted out... and it's not very likely it'd be the pre-set our radio uses. (Only one in the local area, to my knowledge, ever works on 69.)

I like DSC, but for us the distress-related features are the more important...

If we could convince marinas to only respond to routine hails on 9, that'd take a boatload of traffic off 16 -- around here. If we could get people to use the automated channels (when there is one) or channel 9 for radio checks, that'd take another 80% of irritating traffic off 16 in this area.

-Chris

[Dockhead]

Originally Posted by ranger42c

. . But if we were inclined to hail another friend's boat, we'd likely already know the boat's name... and it's faster to just voice hail on 16 (or 9 is better, around here) than it is to key in their MMSI to hail their radio via a DSC call. . . .

Actually, all DSC radios I know have a "speed dial" list. So if you share MMSI numbers among your friends, it's actually faster and easier to call them with DSC. You not only save waiting for air time on 16, you also save agreeing on a working channel.

Having your friends on "speed dial" also allows you to position polling and reporting with them. So a couple of key strokes and you have their position. Maybe not needed if everyone is running AIS.

I use position polling and reporting between the dinghy and mother ship -- it's actually quite useful. If the crew are running around on the dinghy somewhere, and you want to know where they are.

[Alan Mighty]

Originally Posted by Rustic Charm

To date, I've not been able to raise any merchant ship using DSC in this area. This summer I'm hoping to find someone I know has DSC to test it. But, so far no one I have asked even has it.

The Australian MMSI database is on-line. You can search it by the name of the vessel (aka Craft name).


Goes without saying that it only works for vessels that are ship stations with an MMSI. Also for LEO, AVCG and other rescue services.


You supposedly can search call signal and vessel registration number, but I've found that is uneven.

I know the reason: the database has not been well maintained. You pay your taxes and ships station fees and what do you get? %$#@&


My sailing boat can be found by name, but not by call sign or state rego number or Offical Number.


Even though the relevant authorities never fail to send an invoice each year for me to renew my ships station license at my residential address in QLD, the MMSI database lists me as having no state rego and being located in ACT. The database does list my call sign, but a call sign search does not work


Try your luck at: https://www.operations.amsa.gov.au/mmsisearch/

[Alan Mighty]

Blow me down!

I idly searched for Rustic Charm. You're there, with your MMSI, existence in TAS, and your ON! No call sign however.

[Alan Mighty]

I'm further amazed that Rustic Charm shows up in a search of the ITU database of vessels, showing your MMSI and ON (called your IMO No.).

You can search the ITU database at: Particulars of Ship stations


I foolishly thought, because searching for my vessel fails, that the Aus authorities did not pass Aus recreational vessel details to the ITU.


Wrong!


They just haven't passed my vessel details.

[hoppy]

I just found my yacht on the ITU database. It was only reflagged to Aus earlier in the year. No call sign for me as I have no HF. When I registered her in Sweden 5 years ago I was given a call sign.

When I reflagged her I bought a new Standard Horizon GX2000 which is supposed to display AIS targets from my AIS so I think I can make DSC calls to targets, but it's not configured correctly so I see none at the moment. Must fix it and try to call someone one day


Sent from my iPhone using Cruisers Sailing Forum

[ranger58sb]

Originally Posted by Dockhead

Actually, all DSC radios I know have a "speed dial" list. So if you share MMSI numbers among your friends, it's actually faster and easier to call them with DSC. You not only save waiting for air time on 16, you also save agreeing on a working channel.

Having your friends on "speed dial" also allows you to position polling and reporting with them. So a couple of key strokes and you have their position. Maybe not needed if everyone is running AIS.

I use position polling and reporting between the dinghy and mother ship -- it's actually quite useful. If the crew are running around on the dinghy somewhere, and you want to know where they are.

Ah, yep, fair enough, good point, we've got that.

OTOH, we don't have any real friends on the water, and only a few acquaintances who know what a DSC (or an MMSI) is. And we don't much care where they are, at any given time. So our speed dial feature is wasting away...

-Chris

[Rorzech]

Originally Posted by Pete O Static

How does sending a digital hail on channel 70 ( DSC ) have more range than a voice message on channel 16?

If you can hail a vessel 75 miles away with DSC and only talk to him when he's 40 miles away. What's the point of hailing him if you can't talk to him.I don't see any keyboards hooked to these DSC radios.

[Dockhead]

Originally Posted by Rorzech

If you can hail a vessel 75 miles away with DSC and only talk to him when he's 40 miles away. What's the point of hailing him if you can't talk to him.I don't see any keyboards hooked to these DSC radios.

Several functions don't necessarily need voice comms:

1. Distress call (the essential data is sent digitally)

2. Position polling

3. Position report


Particular in the case of the distress call -- the extra range is a really good thing.

[Rorzech]

Originally Posted by Alan Mighty

The Australian MMSI database is on-line. You can search it by the name of the vessel (aka Craft name).


Goes without saying that it only works for vessels that are ship stations with an MMSI. Also for LEO, AVCG and other rescue services.


You supposedly can search call signal and vessel registration number, but I've found that is uneven.

I know the reason: the database has not been well maintained. You pay your taxes and ships station fees and what do you get? %$#@&


My sailing boat can be found by name, but not by call sign or state rego number or Offical Number.


Even though the relevant authorities never fail to send an invoice each year for me to renew my ships station license at my residential address in QLD, the MMSI database lists me as having no state rego and being located in ACT. The database does list my call sign, but a call sign search does not work


Try your luck at: https://www.operations.amsa.gov.au/mmsisearch/

MMSI # Does it come in the box with your radio ? Do you apply for it somewhere ? Do you pick one yourself ? What's with it ?

[transmitterdan]

Originally Posted by Rorzech

MMSI # Does it come in the box with your radio ? Do you apply for it somewhere ? Do you pick one yourself ? What's with it ?

You apply for it in your country per local regulations. In the US you can get an MMSI from BoatUS. Go to their web site. This MMSI is only for use in US waters.

In the US you can also get one from the FCC if you intend to voyage to other countries.

[wrwakefield]

Another great contribution, John.

Thank you. I will add a link from our HF/Marine SSB comms page on our blog for reference for others.

I also noted with interest your mention of using an insulated shroud for HF DSC reception. [Jake of CruisingScotts started a separate thread on this topic...]

On that thread I said:

After reading John's mention of using an insulated shroud for MF/HF DSC in his recent DSC Explained post, it peaked my interest as well.

I know the Metz antenna is adequate for Emergency DSC comms, but we are extending DSC on HF to non-emergency comms as well thanks to another great contribution from John.

We want to hail select friends[and be hailed by same] on HF/SSB using DSC per John's explanation and guidelines. [Thank you for this as well...]

If an insulated shroud improves reception over the Metz, then we will make that primary and keep the Metz as back-up.

I will watch with interest.

Thank you again for all of your efforts that benefit so many.

Cheers!

Bill

[kerrydeare]

Originally Posted by Pete O Static

How does sending a digital hail on channel 70 ( DSC ) have more range than a voice message on channel 16?

I cannot provide "chapter and verse" but I've read recently that this is indeed the case. The DSC digital call is evidently easier to send over slightly longer distances, despite the general "line-of-sight" limitations with conventional voice VHF. Perhaps a person more conversant with radio transmission can elaborate, but then ...

[hellosailor]

John- An update on MMSI's. There is now a special "country code" for man overboard devices. Something like 99-###-year-#### where the first digits indicate the special "country", followed by a manufacturer code, then the year is a 4-digit entry, and finally the device number is another four digits. So things that attach to your PFD, etc. and were made for that purpose, can take full advantage of the system. And. For those of us with portable radios. The folks at Nautilus (who make a submersible VHF/GPS/DSC) supply instructions on their web site. Supposedly BOATUS has stopped issuing MMSI's for portables, but the US Power Squadrons still do. Although the form has some required entries like "Vessel Name" "Vessel Length" the folks at Nautilus explain line by line which entries to answer by "N/A" and similarly. So you can flag your MMSI as being in use by a vessel one foot long with a capacity of one, etc. A bit of a kludge, but apparently the acceptable way of allowing the system to work for persons overboard, as opposed to vessels. FWIW.

[kerrydeare]

To a limited extent, I suspect that DSC VHF will never become commonplace unless it is so legislated. My sampling (admittedly narrow and small) is that while the typical recreational vessel obtains an MMSI to comply with AIS transmission requirements, the vast majority of these vessels fail to follow through with programming on board VHF devices to send and (automatically) receive DSC calls.

I have yet to receive a call acknowledgement from the perhaps 40 or 50 vessels recently contacted, even though they show up on AIS and provide MMSI's.

Evidently most folks just don't bother.