MMSI numbers and DSC radios

Radio · Power & sail

An MMSI is the nine-digit identity your DSC radio and AIS transmit. You must program one into a DSC radio before you transmit. Domestic-only boats get one from an FCC-authorized registrar (BoatUS, U.S. Power Squadrons, Shine Micro); licensed boats get theirs from the FCC with the licence (47 CFR 80.5; FCC; NavCen).

What it is and when you need one

• An MMSI is a nine-digit number that identifies a ship station; DSC radios, AIS and some satellite terminals transmit it (47 CFR 80.5; FCC).
• If your radio has DSC, you must obtain an MMSI and program it in before you transmit. Each vessel needs only one (FCC).
• Coast Guard search-and-rescue staff use the registration behind your MMSI to identify a boat in distress and to tell real alerts from false ones, so keep it current (NavCen).

Where to get one

• Domestic use only, no FCC licence needed: register with an FCC-authorized private registrar, which the FCC lists as BoatUS, the United States Power Squadrons and Shine Micro (FCC; NavCen).
• Domestic MMSIs cannot be used internationally (FCC).
• If your boat needs an FCC ship station licence, the FCC assigns the MMSI with the licence on Form 605. The FCC system will not accept an MMSI issued by a private registrar (FCC).
• DSC handheld radios can get their own handheld-format MMSI (FCC; NavCen).

When the boat changes hands

• The MMSI programmed in the boat's radios can pass to the new owner, but the old registration has to be released, or the old FCC licence cancelled, first. Contact whoever issued the number (FCC; NavCen).

Testing DSC and connecting GPS

• Coast Guard Rescue 21 coastal stations answer automated DSC test calls on channel 70, so a DSC radio with a test-call feature can check itself. Never send a distress alert as a test (NavCen; FCC).
• The Coast Guard strongly urges connecting a GPS to your DSC radio so a distress alert carries your position (NavCen).
• Learn how to cancel an accidental DSC distress alert before you put the radio in service; the FCC warns that uncancelled false alerts can bring severe penalties (FCC).

The rules: 47 CFR 80.5

A plain-language summary of federal rules for recreational boats, checked against the rules’ own text and a second source, and written in our own words. It isn’t legal advice. States add rules of their own, and rules change — the links above go to the current official text.