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Spotlight on Digital Selective Calling (DSC) – PART 3

My second article on DSC (November issue of All at Sea) concerned its use in calling other vessels vs. using Ch 16, as most of us currently do.  To do this we need the Mobile Maritime Service Identity (MMSI) number (aka the “telephone number”) of the vessel that we wish to call.

This presents a problem as there is no directory assistance for MMSI numbers. How to get them?

You can just call your friends and ask them, building your personal directory of MMSI numbers in the call list of your VHF. This is great if these are the only folks you wish to talk to; however, what if you want to contact the freighter behind you that looks like it will be close across your path?  Or the cruise ship—it’s hard to tell in which direction it is going, as the lights on the Lido deck obscure the navigation lights.

Well, there’s a small black box called AIS (Automatic Identification System). Yes, this is the same box that Fatty Goodlander extolled the virtues of in the September issue.  It does all that Fatty said and more! In fact, it gives you the MMSI number of any vessel in the area.

With the MMSI number you can ring the ship’s VHF via your DSC and wake the dead (I mean the busy) watch stander and get their attention to converse on any channel that you have pre-selected. As we noted in the previous article, the DSC ring tone is very attention getting—its volume is independent of the setting and also the squelch setting. In other words it WILL be heard.

This, to cruisers, is one of the great features of AIS, combined with the DSC, as you no longer have to keep calling and calling; “dark vessel at such and such lat/long.” Just ring them up!

AIS, as Fatty indicated gives you loads of data about any ship that carries it—in fact, much more than you’ll ever need. A receive-only unit runs $200 and uses very little power. Connect it to a compatible chart plotter or a laptop and “bingo,” the track of vessels becomes crystal clear around you.

We had a receive-only unit for several years and decided to upgrade to a class “B” transceiver.  We now also transmit our information so others can see us. This brings several new features onboard for our trawler, Swan Song. People can call us if they have a reason—very easily. Ships know we are in the area before they can see us, even if the weather is less than clear. They also know our speed, heading, size, and that we are a recreational vessel.

The Class “B” unit sells for $1000 and up, and needs a GPS signal and its own dedicated VHF antenna. As it is transmitting it uses a bit more power than the receive-only units but only about 250 milliamps average power.

At the next level up are the full Class “A” units. These are more than the average recreational boater needs or can even keep up with. Inputting things like the next port, ETA’s, type of cargo—underway, at anchor, moored, etc. gets to be a bit much for most of us. The Class “B” requires none of those changeable parameters that must be updated each voyage. “Plug and play” once you set the base parameters—MMSI, size of boat and type. Simple, but very effective.

Swan Song’s AIS routinely receives vessel data in a 30 mile circle and often we get 50 miles from big ships. This is long before we have them on radar or visual. You see them on the screen with all their info and you can watch them appear on the radar at 15-20 miles and perhaps have a visual at 10-12 miles as you know exactly where to look. It has made our nighttime passages far more relaxed than in the past in heavy traffic lanes. We know what the big boys are doing and only have to watch for the small vessels that are often underway without navigation lights in the Caribbean.

As we all move further into the 21st century, the use of DSC, MMSI numbers and AIS will become standard gear and the ability to operate them as systems is necessary—even for the recreational boater. Together, they greatly increase safety and the ability of first responders to get the alert, know where the vessel is located and make contact with the vessel in case of emergency.

Remember the ultimate alert device, the 406 EPRIB, is also registered with that same ubiquitous MMSI number…it all ties together now in your mind from these three articles…I hope.  A new DSC VHF and/or and AIS makes a great Xmas present!

Editor’s note:  Parts I (October issue) and II (November issue) of this article will be posted for your reference in our Past Issue Archive online at www.allatsea.net.

Dave Cooper spent over 20 years designing & marketing computers, in the U.S. and Japan.  He sailed to the Caribbean in the mid 70s where he ran seasonal private charters throughout the islands for a decade, then worked in the yachting industry in the BVI until 2006. He retired on his classic trawler, Swan Song, and cruises the southern Caribbean.

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