The baseline, in one line
A fixed-mount VHF with DSC, getting position from GPS, with your MMSI programmed in. Everything else builds on that.
DSC (Digital Selective Calling) turns the red distress button into a digital mayday that carries your boat’s identity and, if the radio has GPS, your position. BoatUS notes that the FCC has required new fixed-mount VHF radios sold in the US to have DSC since 1999, so most radios on the water already have it. The common gap isn’t the radio. It’s a radio with no MMSI entered and no GPS connected, which sends a distress alert that says neither who you are nor where you are.
Getting an MMSI
An MMSI is a nine-digit number that identifies your boat on DSC and AIS. The FCC says that if your radio has DSC, you need to get an MMSI and program it in before you transmit. One boat gets one MMSI; multiple radios on that boat use the same number.
| Where you boat | Where to get it | Notes |
|---|---|---|
| US waters only, recreational, not required to carry a radio, under 65′ | A domestic MMSI from an FCC-authorized registrant: BoatUS, United States Power Squadrons, or Shine Micro | BoatUS lists it as free for members and $25 for non-members. Domestic MMSIs aren’t valid internationally. |
| Trips to Canada, the Bahamas, Mexico, or the Caribbean | An FCC ship station license, which comes with an MMSI | FCC-issued vessel MMSIs end in zero and are accepted internationally. |
Keep your registration details current. That information goes into the Coast Guard’s database and is what responders see when your alert comes in.
Connect the radio to GPS
Either use a radio with built-in GPS, or connect it to the boat’s GPS over NMEA 2000 (or NMEA 0183 on older gear). On a boat with a chartplotter, NMEA 2000 is usually the cleaner path: the radio gets position, and some radios can send DSC calls and positions to the plotter. Test it: most DSC radios can show your position on screen, and you can make a DSC test call.
AIS: receive or transmit?
AIS (Automatic Identification System) lets vessels broadcast their identity, position, course, and speed. There are two ways to use it on a recreational boat:
- AIS receive shows you AIS-equipped traffic. Several current VHF radios include a receiver, so you get it with no extra box. You see ships; they don’t see you on AIS.
- A Class B AIS transponder receives and transmits. Other AIS users, including commercial traffic, see your boat on their screens. It needs its own MMSI programming (the same MMSI as your radio) and a VHF-band antenna.
Examples from current product pages: Standard Horizon’s 2026 catalog lists the GX2410GPS with a built-in AIS receiver, NMEA 2000, GPS, CPA/TCPA collision alarms, and optional second-station microphones. Icom’s IC-M510 AIS has an integrated AIS receiver (the plain IC-M510 doesn’t), and Icom’s MA-510TR is a Class B transponder that connects over NMEA 2000 and works with compatible Icom radios for DSC calls to AIS targets. Most current chartplotters can display AIS targets from the network; Simrad, for example, lists AIS receive over NMEA 2000 on the NSX ULTRAWIDE.
Antennas: AIS works on VHF frequencies, so a transponder needs either its own antenna or a purpose-made splitter that lets it share the VHF antenna. Antenna height matters more than almost anything else for range.
A sensible setup by boat type
| Boat and use | Sensible baseline | Worth adding |
|---|---|---|
| Bay boat, inshore and protected water | DSC VHF with GPS and MMSI; a DSC handheld with GPS as a backup | A radio with an AIS receiver if you cross or fish near shipping channels |
| Center console, nearshore and offshore | DSC VHF with GPS, MMSI, and AIS receive, tied into the plotter over NMEA 2000 | A Class B transponder, especially in fog, at night, or around commercial traffic; a handheld for the ditch bag |
| Small cruiser, coastal weekends and overnights | DSC VHF with GPS and MMSI, plus a Class B transponder | A second-station mic at a second helm or cockpit; an FCC license if you cross to the Bahamas or Canada |
Habits that matter more than hardware
- Make sure the MMSI is entered and the radio shows a GPS position before the season starts.
- Know where the distress button is and what it sends. Make a DSC test call.
- Keep registration details (boat description, emergency contacts) up to date.
- If you have a transponder, check that other boats or an AIS app can see you.
- I have an MMSI that matches where I boat (domestic or FCC).
- It’s programmed into every DSC radio and any AIS transponder on the boat.
- The radio gets GPS position, built-in or over the network.
- I’ve decided between AIS receive only and a Class B transponder based on where I run.
- The antenna plan covers both VHF and AIS.
This guide is for planning and for asking better questions. It is not an installation manual. Wiring, fusing, and battery work should follow ABYC standards and the equipment maker’s instructions; if you’re not sure, have a qualified marine electrician, ideally one who is ABYC-certified, design or check the work.
Product names here are examples, not endorsements, and nothing on this page is a paid placement. Some links may become affiliate links once those programs are set up; if they do, it will say so, and it won’t change what we suggest.