Set Up Your VHF Radio: MMSI, DSC, GPS Hookup and Radio Checks

Look at the radio for a red DISTRESS key (often under a spring cover) and a DSC menu. Check whether the display already shows an MMSI. BoatUS suggests checking the manual for how to display it, or placing a private DSC call to a friend and asking them to read back the MMSI that shows on their screen. If you bought the boat used, the old MMSI may still be registered to the previous owner. An older radio with no DSC menu or red key cannot send a digital distress alert at all; the Coast Guard advises that any new radio you buy include a GPS receiver so its alerts carry your position.

According to the Coast Guard and BoatUS:

• U.S. waters only, recreational boat under 65 feet, not required to carry a radio: you do not need an FCC license. Get an MMSI from an organization the Coast Guard lists, such as BoatUS (free for members, $25 otherwise at the time of writing), America's Boating Club (U.S. Power Squadrons) or Shine Micro.
• Planning to visit or talk to foreign ports (Canada, the Bahamas, Mexico, the Caribbean) or required to carry a radio: you need an FCC Ship Station License, which comes with its own MMSI. BoatUS notes that a BoatUS MMSI cannot be reused for international use; you would reprogram with the new FCC number.
• A handheld used on more than one boat: consider a separate MMSI for the handheld, so you can update its registration to whatever boat it is on.

The registration goes into the Coast Guard's search and rescue database. Rescuers use it to learn who you are, what your boat looks like and who to call, and to tell a real alert from an accidental one. Fill in your boat's description, emergency contacts and other safety gear (BoatUS asks for your EPIRB ID too; the EPIRB itself is registered separately with NOAA). Update it whenever anything changes.

Follow your manual's menu (often called "User MMSI" or "MMSI setup"). Many radios let you enter your MMSI only once or twice; after that, a dealer or the manufacturer must reset it. So type slowly and confirm every digit before saving.

If you have more than one radio on the same boat (a fixed mount and a handheld kept aboard), BoatUS says to put the same MMSI in all of them.

If your radio has a built-in GPS, check that it shows your latitude and longitude on screen. If not, connect it to your chartplotter or GPS:

• NMEA 0183: usually two wires. Connect the GPS's data-out (+) to the radio's data-in (+), and join the data ground (-) wires. BoatUS warns there is no standard color code, so use both manuals.
• NMEA 2000: plug the radio into the boat's backbone with the proper drop cable, if it supports N2K.
• Make the joints with crimped butt connectors and adhesive-lined heat shrink.

Turn everything on and confirm the radio now shows your position and time. If the screen shows "no position" or a flashing position, the distress alert will not send a usable location.

• Power: the radio should have its own fuse or breaker. BoatUS recommends wiring the negative to a ground bar and the positive to a dedicated breaker sized as the radio maker specifies, with wires supported every 18 inches.
• Antenna: VHF works by line of sight, so height matters. Check that the antenna is upright, its mount is tight and not cracked, and the cable is not crushed, kinked or chafed.
• Connector: the coax plug at the back of the radio and any connection at the antenna base should be clean and dry. Green corrosion or water inside a connector costs a lot of range. Seal exposed connections with self-amalgamating tape. BoatUS notes that solder-on PL-259 connectors make a longer-lasting connection than crimp-on ones.

The Coast Guard says a VHF radio's range is generally 5 to 10 miles between boats and at least 20 miles to a Coast Guard station, depending on antenna height. A poor antenna or connection can cut that sharply.

This is the right way to check DSC. All U.S. fixed-mount radios sold since 2011 must have a test call feature. Per the Coast Guard:

1. Store the Coast Guard's group number 003669999 in the radio's DSC directory.
2. Choose Test Call in the DSC menu.
3. Select the stored Coast Guard number and send.

Your radio should show an acknowledgment from a Coast Guard station within a short time (its number may differ from the one you entered). If you get it, your radio, MMSI, antenna and the Coast Guard's Rescue 21 system are all working. You can also send a test or routine DSC call to a friend's MMSI.

The Coast Guard asks boaters to do voice radio checks with other boaters on Channel 9 and not on Channel 16. The Coast Guard does not monitor Channel 9. The automated radio check service that Sea Tow ran on Channels 24 and 28 was discontinued in October 2020.

A short, polite check: "Radio check, radio check, this is [boat name], how do you hear me, over." Thank whoever answers and move on.

• Channel 16 is the distress, safety and calling channel. FCC rules require boaters with a VHF to listen on Channel 16 (or Channel 9, the supplementary calling channel for recreational boats) whenever the radio is on and not being used to talk. The Coast Guard recommends staying on 16.
• You may hail another boat on 16, but keep it brief and move to a working channel right away (for example, "Reply 68").
• Channel 70 is reserved for DSC digital signals only. No voice on 70.
• The Coast Guard announces storm warnings and urgent broadcasts on Channel 16 first, then moves to Channel 22A.
• Weather channels (WX): your radio's weather button tunes NOAA Weather Radio, the National Weather Service's continuous broadcast from more than 1,000 transmitters, on seven frequencies the radio usually labels WX1 to WX7. Find which one is strongest where you boat and listen before you leave. Many radios also have a weather-alert mode that sounds when NWS sends a warning; check your manual.
• No chatter, music, profanity or fake emergencies. Hoaxes carry fines and possible prosecution.

DSC distress: lift the cover over the red DISTRESS key and press and hold it until the radio confirms the alert is sent (usually a few seconds; check your manual). Many radios let you pick the nature of distress first (fire, sinking, man overboard) if you have time. Then the radio switches to Channel 16: follow up with a voice MAYDAY.

Voice MAYDAY (Coast Guard format), on Channel 16:

• "MAYDAY, MAYDAY, MAYDAY. This is [boat name] (three times), [registration number]."
• "MAYDAY, [boat name]. My position is [lat/long, or bearing and distance from a landmark]."
• What is happening (sinking, fire, injury) and what help you need.
• Number of people aboard and any injuries.
• Boat description: length, type, hull color.
• "Over." Then listen, and repeat if there is no answer.

Tape a card with this script next to the radio so a guest can use it if you are hurt. After the call, stay by the radio if you can: the Coast Guard can home in on your transmissions.

Pressed DISTRESS by accident? Per the Coast Guard: do not switch the radio off (most radios keep sending the alert when powered back on). Use the radio's cancel-distress menu to transmit a cancellation, then call on Channel 16 and tell the Coast Guard and nearby boats you are cancelling, with your boat's name and MMSI. You will not get in trouble for an accidental alert that you cancel right away.

Hear a distress alert or MAYDAY? Listen on Channel 16 and check the position shown on your radio. If nobody answers a distress call and you are nearby, you are expected to respond. If a DSC alert is not acknowledged by the Coast Guard, contact them by any means you have and pass on the details.

Show everyone aboard where the radio is, how to turn it on, where Channel 16 is (most radios have a 16/9 key) and what the red button does. Remind kids it is not a toy.

When you sell the boat or the radio, update or transfer the MMSI. BoatUS explains that if the radios stay with the boat, you transfer the MMSI to the new owner; if you keep the radios, update the registration with your new boat. Two boats must never use the same MMSI. When you buy a used boat with a DSC radio, find out whose MMSI is programmed in before you rely on it.