Sunday, February 22, 2015

Digital Selective Calling

Or DSC as it is commonly referred to in any VHF radio manual or on chat groups, is an important tool.  All fixed mounted modern marine VHF radios come with DSC these days.  This feature allows you to directly call any vessel with an MMSI number that is within VHF range.  Remember the MMSI?  We have discussed it here before FCC Licensing -Clear As Mud .  In short, you get your MMSI number when you apply for and get your ships radio license.  In our case from the FCC.  Note:  US boaters planning to leave the USA waters should only get their MMSI number from the FCC and not the free one from BoatUS.  The BoatUS MMSI number is only good in the USA.  The FCC assigned MMSI number is good internationally.

Anyway....  Normally cruisers monitor channels 16 and 68 on their VHF radios.  If they want to hail another boat they usually do so on 68 and then move to another open channel (like 69) to talk.  Of course anyone listening can follow along and listen too.  Definitely a party line sort of system.  However, if I have another boat's MMSI number, I can use the DSC feature on my VHF to call them directly on the VHF radio.  It actually rings rather loudly like a phone on their end.  Once the other vessel answers, it automatically takes them to the open channel I selected.  The conversation can still be heard by others listening to that channel or any vessels that has their radio set on scan.  But the nice thing is that everyone doesn't have to listen to you hailing other vessels throughout the day.  This can get to be a bit much for others if you are trying to plan an outing or solve a problem or such.  It doesn't take long to identify the social butterflies, buddy boats or kids boats in an anchorage as they are hailing frequently.  Imagine hearing "Mousetrap, Mousetrap, Mousetrap, this is Blowhard.  Come in please."  "This is Mousetrap."  "Oh hi.  How are you?"  "Good.  How are you?"  Good.  Can we go to 67?"  "Going to 67."   multiple, multiple times throughout the day.  Argh!  Unfortunately, we have been guilty of this at times in the past.  Now we are trying to use DSC as much as possible.  

There are other great benefits of DSC.  A couple of big ones are as follows.  If you have an AIS (automated identification system) receiver then you will see the ship names and MMSI number for bigass ships.  It is my understanding that by law (maritime law I guess) they are required to have AIS and transmit.  Normally when we see a giantantic ship (usually at night...why is it always at night), we hail them on the VHF radio and say something like "Hello Captain.  I am the little tiny sailboat off your port bow.  I just wanted to be sure you see me.  Please don't run me over.  We will try to stay out of your way."  However, even though they are required by law to answer your hail, it doesn't always happen.  Some ships have a frighteningly low number of crew.  Special Note - they respond better to a female voice hailing them verses a male.  With DSC, we can simply call them directly, waking them up on the bridge with a loud ringing from their VHF radio.  Additionally, the call is then logged in their radio and yours, provided neither deletes the log.  Having a record of a VHF hail to a big ship might be a good thing.  You can also receive and send position reports.  This means I can actually send my exact position to the bigass ship.  Sort of a...." is where my little tiny sailboat is.  Please don't run me over."  only using your lat and long position to say it!  Another good thing about DSC calling speaks to something I mentioned before, privacy, even if it's limited.  Because it rings another boat directly and then automatically goes to another channel you selected, fewer people can follow and hear your conversation.  Since many of our conversations are about events and activities, fewer people hear the details of your comings and goings and thus fewer people know when your boat is occupied and when it's not!  

The interesting thing that we are finding is that most cruisers don't use the DSC feature.  It seems most don't know how to use it and haven't taken the time to learn.  We were guilty of this but I thought it was because we are still newbies.  No....many seasoned cruisers don't know how to use it.   You need a buddy boat to try it out on.  We did our learning with s/v Allergro while in Trinidad.  In return, we recently answered numerous rings from s/v Karinya as they learned to use theirs.  "Bloody hell!  I've read 71 pages of this VHF manual.  It's actually quite interesting."  

If you have a marine VHF with DSC, do you use it?  Do you know how?  If not, maybe find a buddy boat and give it try.  I think you might like it.  FYI- some cruisers actually put there MMSI number on their boat card.  We did.  

Final Note - I am NOT a VHF radio expert.  For that matter....  I am not a MMSI, or AIS or bigass ship expert either.  The above is simply based on our experiences and discussions with a few seasoned cruisers.  

1 comment:

  1. Had an interesting experience the other day with DSC. We ad turned our radio off and gone to bed and when I turned it on in the morning to get ready for our day's sail, there was a distress message stored in our message log. Someone had sent a distress DSC call the night before at 6:50pm. I tried to respond to their call but got no answer. Being out of range of the Coast Guard (we were at West End Bahamas), we sent an email to a good friend of ours in Homeland Security who forwarded it on to the CG Miami. They located the boat and discovered that the message had been sent out accidentally. The boat was safe in Miami after a crossing. Just wanted to mention this because the little message envelope can be easy to miss on the screen.

    Great post. Very informative.

    S/V Kintala