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SESK: Stuff Everyone Should Know · sesk.info/boat-mmsi-nine-digits

What is an MMSI, which you need for a DSC marine radio?

A nine-digit number that identifies your boat's radio.

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  1. A nine-digit ID number for your boat's radio ✔
  2. Your boat's state registration number
  3. A radio channel used for weather

Why: A Maritime Mobile Service Identity (MMSI) is a nine-digit number used by DSC radios and AIS to identify a vessel. Recreational boaters can get one from approved groups like BoatUS.

Huh, didn't know that: Without a registered MMSI, rescuers can't match your DSC alert to your boat's details.

The dad joke
Why did the radio need nine digits? Because eight just wasn't enough to call home.
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References

Answer: A nine-digit ID number for your boat's radio. A Maritime Mobile Service Identity (MMSI) is a nine-digit number used by DSC radios and AIS to identify a vessel. Recreational boaters can get one from approved groups like BoatUS.

  1. USCG NAVCEN, Maritime Mobile Service Identity www.navcen.uscg.gov/maritime-mobile-service-identity
    Maritime Mobile Service Identities (MMSIs) are nine-digit numbers used by maritime digital selective calling (DSC)
    Checked 2026-10-09.

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