Digital Selective Calling

[LarryandSusanMacDonald]

Hi, Folks,

We haven't posted much on Sailnet in quite awhile. We've been out cruising and AT&T isn't too long on the bandwidth for the internet. But now we're back in a slip in Galesville, Maryland and working on the Frugal Mariner, our website.

I've had a couple of requests for a page on VHF radio and it's protocols, which I'm working on and a question came to mind that I'd like to put to this forum.

Regarding the DSC (Digital Selective Calling) on our VHF radios: Many of us, including myself, have connected our GPS to the VHF so that the DSC distress function will work properly. And we've all registered our MMSI numbers (my,gawd, I'm writing in initials).

But there's another function for the DSC and that's the channel 70 hailing, where you can hail other boats if you know their MMSI code. Or you can hail the Coast Guard if you know their MMSI codes (which are published - but that's another discussion).

My question is: Is anybody using this feature? Cruising clubs, yacht club members, or cruiser's nets could find this feature quite handy, but I haven't heard of anybody using it. Am I somehow just out of the loop or is this feature just universally ignored?

[sailingdog]

I've used the feature, and hailing boats via their MMSI number is very useful. This is particularly true if you have to deal with commercial ships and have AIS aboard, since the AIS will give you the MMSI for any traffic that is shown. In many cases, using someone's MMSI and DSC to communicate with a large commercial ship makes it much simpler to do so. They may fail to hear you hail them on channel 16, while the DSC hail will generally get answered.

[SVAuspicious]

I use it.

To avoid having to listen to the chatter on cruiser's channels (like 68 in Georgetown Exuma) I give my MMSI to friends who can call me using DSC if they like. Most grump at me for not keeping the radio on 68, a few turn around and ask for my cell phone number, and a very few use DSC to call.

People around home that I sail with regularly use my group DSC number (only properly available if you have an FCC issued MMSI, not the Boat/US or other alternative MMSI numbers) to hail each other. This has turned out to be easier since we all have the group ID programmed into the radios.

Finally, I use a Standard Horizon 850 handheld VHF as a dinghy radio. The handheld has a GPS and supports DSC. This makes calls between the dinghy and the boat really easy. Note that some radios don't channel switch properly when called with the same MMSI programmed into them. If I had it to do again I'd get a 'ghost' MMSI from Boat/US specifically for the handheld using the dinghy registration details.

[lshick]

I have not used it, nor have I heard of anyone in the US who has, with one exception: if you have an AIS unit, you can get the MMSI of a ship coming at you. With the right integration, you can "push their button" and ring the bell on their VHF. I've read that you're much more likely to get a response that way than by hailing "Ship at latitude xx, longitude yy..." However, I've also heard from folks who had the opposite experience: AIS did not display the target's name, only the MMSI, and there was no response to an attempt to connect via DSC.

Of course, the USCG is now advising everyone to turn off the "automatic channel switching" function of DSC, which is one of the major calling cards of the technology. Good luck if you have an old unit that doesn't have that function. Maybe DSC will grow up some day.

[LarryandSusanMacDonald]

Good information. Thanks guys. The AIS thing is on my want list - at least the receive only device. And it's good to know about the ship / MMSI ID.

Ishick - any idea why the CG is discouraging the DSC auto channel switching?

[noreault]

The problem with auto channel switching is that you may be involved in a critical communication and are suddenly switched. For instance, giving instructions to a tow or tug.

[LarryandSusanMacDonald]

Ahhh, makes sense. Don't you just love hi-tech?

[Zanshin]

EU countries have, for several years, not allowed registration of new non-DSC ship radios.
DSC isn't in use very much in the US and Caribbean, I had my radio on much of the time for a 6 month period cruising around the Leewards and Windwards and have only 7 logged DSC messages, 3 of which were for the same MAYDAY/PANPAN event!

[Vasco]

Use it all the time in the Bahamas to call my friends. Once you use 16 all the busybodies follow your conversation.

[sailingdog]

Another place DSC is useful is when out fishing. You can use it to send your location or request the location of your friend's boat without having to say the location over the air. This means you can coordinate fishing without giving your position away over the radio.