Digital Marine Communications – A Primer
Chapter 1: What is it and Why the Hoopla?
Robert Hellier, HYC Senior Member & Marine Engineer
In this chapter about digital marine communications, I wish to explain, in straightforward language and by examples, the advantages of acquiring one of these digital devices for your sail or power boat and how they can positively contribute to your activities on the water. I will discuss Very High Frequency Digital Selective Calling (VHF-DSC) radios and Maritime Mobile Station Identity (MMSI) numbers, both of which are key parts of the international Global Maritime Distress and Safety System, or GMDSS.
Let’s start with brief layman’s descriptions of VHF-DSC and MMSI:
VHF-DSC Radio – At first glance it doesn’t look that different than your old analog VHF. It is a box with a dial and a screen or knob showing your VHF channel options. It has a microphone attached to a curly cable. In fact, you can use it just like your old radio and that’s exactly what many boaters do, initially. On closer inspection, however, you do see several important differences on the outside:
It’s got a bigger price tag than your old radio!
It has a red “DISTRESS” button, typically protected by a flip-up cover
It has a much larger menu of options, accessible by several hard and soft keys. Naturally the manual is thicker as well!
It has a few more connection ports on the backside, particularly one or more NMEA ports
Inside, it is completely different than your old VHF. Although it uses the same VHF wavelength spectrum as your old radio, the similarities end about there. Your old radio modifies the amplitude and frequency of the airwaves to broadcast voice over a distance to all other VHF radios within range. A VHF-DSC, however, only uses the VHF channels as a transport medium. Instead of broadcasting sound waves, it selectively sends and receives digital packets of information between two or more VHF radios within range. These packets contain digitized voice, but also a variety of other vital information such as sender and receiver information, message priority, encryption and many other bits of info. The implications of digitized packaging of information over the VHF radio range are enormous and we’ll demonstrate some of them later in this chapter.
MMSI – Do you have a phone? Then you’re familiar with the ubiquitous 11-digit telephone number.
We know that 1-416-234-5678 means that the person that owns this number lives in North America (1) and Toronto (416) and that the next 7 digits are specific to an address or cell phone user within this region. You got your own number by asking for one from your phone company or cellular network provider.
MMSI is basically a phone number for a vessel’s VHF-DSC radio which in government parlance is your “Ship Station”. It is composed of 9 digits, however, and is assigned by Transport Canada, for free!
Ship station MMSI’s registered in Canada all start with the digits “316”. These are called the Maritime Identification Digits (MIDS). The remaining 6 digits designates the specific VHF-DSC ship station. For example, our sailboat “DragonHeart” has an MMSI of 316019319. If you ever see DragonHeart out on the lake, Call me! It’s good practice for you and me.
Or, if you’d rather talk to somebody else you can look up the MMSI of any Canadian registered vessel by visiting the Industry Canada spectrum direct website at https://sd.ic.gc.ca/pls/engdoc_anon/mmsi_search.Ship
Besides vessels, other entities can be assigned an MMSI. These include shore stations that participate in GMDSS activities and SAR aircraft. Shore stations and SAR Aircraft have distinctive MMSIs to aid in recognition:
Coastal stations all start with “00” followed by their MID, then a 4-digit specific number of the particular station. For example, the Canadian Coast Guard station in Prescott has an MMSI of 003160026.
SAR Aircraft all start with “111” then the 3- digit MID then a 3-digit identifier. Therefore, a Canadian registered SAR aircraft (fixed or rotary wing) will follow the format “111316XXX”. .
Aids to Navigation and Automatic Identification System (AIS) devices can also be assigned MMSIs.
Some questions are probably popping up in your mind right now. Let’s see if I can guess them:
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Description texAbsolutely! There is no separation within the VHF spectrum between old style and VHF-DSC. Perhaps the only difference you’ll encounter is better sound quality of the voices you hear on your VHF-DSC, due to sophisticated digital sound filtering algorithms that distinguish voice from noise and static. That’s already worth some of the extra money you spent!t goes here
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Unlike a phone, which is useless if it doesn’t have a telephone number, a VHF-DSC radio can be used without an MMSI number assigned to it. You can use a VHF-DSC just like your old VHF by just installing it in the same place, plug it in, attach the antenna, turn it on, select a channel and listen or press the microphone to talk.
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You can take advantage of some of the features in limited ways and other features not at all. This will become apparent to you later in this chapter.
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It is not difficult or time consuming, though you must fill out a form and submit it to Transport Canada, either online or at a district office. This process will be explained in more detail in chapter 2, next month. If you really need to know NOW, just jump to the following Industry Canada webpage http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01032.html#s7.2
So, what’s the big deal?
Do you recall when GPS devices for boats first became available on the market? Did you pooh-pooh them? After all, what was wrong with paper charts? Well nothing really. Mariners have been using them for centuries and had no particular issues – other than an occasional misjudging of course, track, speed and position by a fairly wide margin, resulting in an embarrassing loss of a vessel on a shoal or against a headland.
Nowadays, with ubiquitous GPS devices and their satellite networks, we can pretty much take for granted that we know the coordinates and course details of our vessel to a very precise degree. This brings peace of mind and security to our sailing that would’ve been very hard to replicate in the era of paper charts, line-of-sight navigation, dead-reckoning and sextants.
Just as digital tech and satellites have transformed marine navigation, so too is it transforming marine communications. “But wait!” you interject, “Why all this fuss about digital VHFs? I’ve been using my trusty old VHF for decades and am quite happy with how it works. Why should I spend several hundred dollars of hard earned money on a new fandangled radio?”
If you were thinking that, you can join what was once a very large club. The maritime industry is, after all, a conservative and sceptical group of people who will almost always opt for the “tried and true” over “novelty”. In fact, DSC-VHF radios and MMSI numbers were slow to be adopted by recreational boaters and smaller commercial operators when they first came on the scene in the mid 2000s. As the system has matured, however, adoption has been swift.
So, perhaps it’s now time to ask another question, “Why are these things becoming so popular with the sailing community?” Perhaps the best way to answer that question is to describe a couple sailing scenarios and compare how they would play out with an old VHF versus a VHF-DSC with an MMSI.
Scenario 1
Calling a buddy on his boat during a cruise
Old VHF - On channel 16/67, you make a call out to your buddy’s boat by its name, which can be heard by everyone within 40 nm. He replies, saying to switch to another channel. You switch but you must wait awhile because another vessel is transmitting some useless information about the skipper’s night out, current hangover and how few fish he’s caught this morning. Finally, you get through to your buddy and try to have a quick conversation about destination, ETA, etc. because you know that others are listening, and waiting to do their VHF business as well. All these conversations are heard by everyone, distracting all of us from two of the great pleasures of boating – peace and quiet.
VHF-DSC with MMSI - You call your buddy by keying in his 9-digit MMSI on your VHF-DSC’s keypad (or if you preprogrammed it, by pressing a few keys to get to your list), selecting a voice channel and pressing DSC CALL. His radio automatically switches to your chosen voice channel and rings him! He answers, and you directly enter your uninterruptable conversation. Because the radio call is digitally encoded and packaged between your respective MMSIs, your conversation is totally private! It also does not impede others from making MMSI or open channel calls of their own. Not even the unknown vessel that’s been trailing you for the last hour can hear your conversation. You take your time and feel secure to provide whatever information you desire to your buddy, knowing that it cannot be misused by others. Remember when you asked about using a VHF-DSC without an MMSI assigned to it? Well, in that case you lose all the benefits described above, except for improved sound quality.
Scenario 2
Making a Distress Call
Old VHF - You realize that something is terribly wrong with your vessel and that the good ship and crew are in danger. You go below to your boat’s VHF and call out “MAYDAY, MAYDAY, MAYDAY (3 times). THIS IS SAILING VESSEL SEASHELL, SEASHELL, SEASHELL…”. While trying to remain calm, you relay the other important information that will be needed by the SAR centre: Type of vessel, number of crew on board, nature of distress. They receive your call and request your position. Drat! You climb back up to your cockpit’s binnacle mounted GPS, fumble for a pen and jot down the lat/long onto the back of your hand, but your hand is wet and the ink won’t hold. You look around for some paper or try to remember the numbers, get back to your radio and relay what you have, hoping you got it right. After all, your crew’s lives depend on you not having made any error and accidentally sending the SAR team to the middle of Saskatchewan instead of your actual location on Lake Ontario. This all takes time, especially as the quality of the signal is not great and you have to repeat some information requested by the SAR dispatcher. Meanwhile the emergency is getting worse and your crew need direction which you cannot provide while you’re still on the radio…
VHF-DSC with MMSI - Realizing that your vessel and crew are in mortal danger, you go to your VHF-DSC, flip the protective cover on the red button marked DISTRESS and press it for a few seconds. The distinctive alarm is emitted. You can also select from a menu of emergency types (FIRE, FLOODING, COLLISSION, CAPSIZE, GROUNDING, PIRACY, SINKING, ADRIFT, MOB or ABANDONMENT) to include in the digital signal sent to the coastal station. You look at your VHF-DSC’s screen and you see that the lat/long of your vessel’s current position is also there, sent continuously by your GPS. You rest assured that this vital information has been automatically included in the transmitted digital message.
Your VHF-DSC now gives a RECEIVED ACK message, indicating that a coastal station has received your distress call. At the coastal station, their operators have instant access to all that information that you gave when you first applied for your MMSI, such as name and description of vessel, owners’ names, emergency contact information, typical number of crew onboard and so on. With all this information already in the station’s hands, you only need to confirm that you are in actual distress and needing assistance. Now you can concentrate on dealing with the actual emergency and directing your crew until help arrives…
There is an assumption made in this scenario, namely that you’ve gone to the trouble of linking your GPS to your VHF-DSC through an NMEA cable. If you have both devices you really are crazy not to, given how easy it is to do and the benefits of doing so. If you didn’t have a GPS sharing its data with your VHF-DSC and no MMSI assigned to the radio, you do loose most of the benefits of making a digital distress call. Really the only thing that you get to keep is the simplicity of pressing the DISTRESS button and knowing that it’s going to get everyone’s attention. Otherwise the SAR dispatcher will still have to ask you for critical position and vessel/crew information, taking up precious time that would be better spent dealing with the actual emergency.
Convinced? If these two scenarios didn’t inspire you to replace your analog VHF very soon then you are either a true man of steel or of a sado-masochistic tendency. Then I hope your crew is also! Besides illustrating the advantages of digital marine radio, the two scenarios give us two very important take-aways that I will finish with, namely:
If you haven’t yet installed a VHF-DSC radio on your vessel, you miss important safety features and conveniences within the Global Maritime Distress and Safety System that would make your boating much more secure and pleasurable.
Even if you have a VHF-DSC radio for your vessel but haven’t applied for and received your individual 9-digit MMSI number, you are only able to use a fraction of the features that the technology – supported by GMDSS - is capable of.
Happy sailing, but do get that GPS connected to your new VHF-DSC !
