If you own a boat with a VHF radio, an AIS transponder, you know you need an MMSI (Maritime Mobile Service Identity) number. It is the “digital phone number” for your boat that allows the Coast Guard to identify you in an emergency.
Most boaters in the United States get their MMSI for free (or a small fee) through organizations like BoatUS, Sea Tow, or the U.S. Power Squadrons.
But here is the catch: If you plan on pointing your bow toward the Bahamas, Mexico, Canada, or anywhere else outside of U.S. domestic waters, that “free” MMSI is legally invalid—and could lead to a massive headache at the customs dock.
The Difference: Domestic vs. International
There are two distinct databases for MMSI numbers in the United States.
1. The Domestic-Only MMSI (BoatUS / Sea Tow)
These numbers are issued under an agreement with the FCC to simplify things for boaters who never leave U.S. waters.
- The Pro: It’s fast and usually free.
- The Con: Your boat’s data is stored in a private database.
- The Limitation: International search and rescue (SAR) organizations in other countries cannot access this database. If you are in distress in the Caribbean, the local authorities won’t know who you are.
2. The International MMSI (FCC Issued)
This number is issued directly by the Federal Communications Commission (FCC).
- The Pro: Your boat’s data is uploaded to the ITU (International Telecommunication Union) database in Geneva, Switzerland.
- The Con: The registration process is notoriously difficult, involving the archaic “FCC ULS” website.
- The Requirement: This is the only MMSI legal for international travel.
Three Reasons You Need an FCC-Issued MMSI
1. Customs Compliance
When you clear customs in countries like the Bahamas, you are often asked to show your Ship Station License. A BoatUS certificate is a membership perk; an FCC License is a legal federal document. Many cruisers have been fined or turned away because they lacked the proper international radio authorization.
2. AIS Functionality
If you have an AIS (Automatic Identification System) transponder, your MMSI is broadcast to every ship around you. If you are using a domestic-only MMSI in international waters, you are technically broadcasting an “unassigned” or “illegal” identifier. In busy commercial shipping lanes, this can draw unwanted attention from foreign coast guards.
3. Search and Rescue (The “Life” Reason)
In a true emergency offshore, your DSC-enabled radio sends a digital “Mayday.” International rescue coordination centers check the ITU database first. If your MMSI isn’t there because it was a “domestic-only” number, they won’t know your boat’s name, length, or emergency contact info. That delay can be fatal.
Can I just “upgrade” my BoatUS number?
No. Unfortunately, the FCC and BoatUS use different number blocks. If you decide to go international, you must apply for a new Ship Station License through the FCC. This will issue you a new MMSI number, which you must then reprogram into your VHF and AIS units.
The Easy Way: Get Your International License Today
The biggest reason boaters stick with domestic MMSIs is that the FCC website is a nightmare to navigate. Between the “CORES” registration and “Form 605,” most people give up halfway through.
That’s where ShipRadio.net comes in. We’ve automated the entire process. We handle your FCC account setup, your Ship Station License, and your Restricted Radiotelephone Operator Permit (RR) in one simple, 5-minute form.