Getting the Most Out of Your DSC Radio

Just about every boat has a DSC equipped radio, yet it remains one of the most overlooked pieces of technology on board. To help you understand how to leverage this technology and make radio communications easier, first we need learn about what DSC is.

Digital Selective Calling (DSC) uses a dedicated channel (70) to broadcast a digital package over your VHF in a fraction of a second; similar to how your cell phone sends a text message. Contained in this message is your current coordinates, the nature of the message, and the heart of the transmission, your MMSI number. Utilizing DSC on board can eliminate hailing over 16 (or voice communication all together) leaving this emergency channel open for higher priority uses. Anyone who boats on the Bay will inevitably hear two boaters using 16 to have a long drawn out conversation, or my personal favorite: the guy who decides that everyone on 16 needs to hear the full rendition of stairway to heaven. Next time you come across one these buffoons, think about what would happen if you had an emergency and couldn’t reach the Coast Guard for the next 7mins and 55seconds while we wait for Led Zeppelin to finish up their set. If your VHF is set up correctly, you can still get your MAYDAY out immediately and follow up with voice communications later.

So what do you need to get started using DSC? First and foremost you need to have a DSC capable VHF. An easy way to check is to see if it has a “Distress” button, usually found under a protective cover. If your radio lacks this feature, it’s time to upgrade! A VHF is the best resource in an emergency so it’s a no brainer to make sure yours is reliable and has all the modern safety features available. If your radio is DSC ready, the next step is to make sure it is hooked up to a GPS source. Most VHF’s on the market will connect to your plotter via NMEA0183, but the better ones will either have their own built in GPS receiver or use the NMEA2000 network. This connection is often overlooked by DIY and professional installers alike, but being able to instantly broadcast your exact location is critical. If your VHF does not display your current coordinates, make this connection ASAP!

Now that your VHF is getting GPS data, you need obtain a MMSI (Maritime Mobile Service Identity) number. There are two sources for these numbers, the FCC ( and authorized boating organizations such as Boat U.S. The first question I always ask my customers is: do you think you will ever take your boat into international waters? If your answer is yes, you MUST get your number issued by the FCC. There is a fee for this and a bit of paperwork, but you will end up with a number that is legal word-wide. If your answer is no, head over to Boat U.S. or a similar organization and you can get a number for free in just a few minutes, however this number can only be used in US waters.

So what is the purpose of registering for this number? Included in the application, you will fill out information such as who owns the boat, the boats name and registration numbers, what the boat looks like, and who your emergency contact is. This information is stored with the Coast Guard (internationally for a FCC registration) and can be retrieved when needed. If you were to have an emergency, in an instant the Coast Guard now knows where you are and the name and description of the vessel, as well as who to contact on shore if they need more information, even though the second verse is just starting to play on 16.

DSC can also be used for non-emergencies as well. Most radios will have a directory in them where you can store your buddies MMSI numbers. With the push of a button you can ring their radio and ask them to tune to a working channel, all while staying off 16. You can also send your position to them or ask for theirs and push it to your plotter, think of it as a manual AIS system. You can even program in a second group MMSI and keep tabs on the whole flotilla with ease. Additionally you can perform an automated DSC radio check either to a friend’s radio, or the USCG using MMSI 003669999.

Finally we come to the biggest source of confusion and lack of information I see with my customers: “I just bought a new boat and I can’t wait to use it!” Assuming the last owner set their VHF up correctly, it will still be programed with their MMSI number. When you buy a new boat, the last thing on your mind is the VHF, but it is very important to get your MMSI registration updated. While it is possible to transfer a MMSI, unless you have the old owner on hand ready and willing to deal with canceling their old number and authorizing the transfer, you will need to remove the old number and program in yours. However most VHF’s will not allow users to change this number themselves so it must be returned to the manufacturer to be re-programed. Luckily if your VHF is a Garmin model, Tidewater is a Garmin authorized installer, so we have dealer tools that will allow us to reprogram these radios onboard saving removal and shipping fees as well as the delay.

While all of this leg work to connect, register, and program may seem like a pain, once you begin using DSC to its fullest, you will never know how you managed without it. So read up on your VHF’s manual and enjoy DSC while cruising the Bay this summer! Until then, Bill standing by on 16. (and 70!)
Bill Brandon
Garmin Certified Installer
ABYC Certified Technician
NMEA Trained in Advanced Marine Electronics Installation and Advanced NMEA2000
FCC GROL# PG00056239
Tidewater Yacht Service, Baltimore, MD