Proper Procedure for Changing Your AIS MMSI When Re-flagging Your Boat

A crucial safety and legal guide for cruisers changing their vessel’s flag state

Hello fellow boaters,

I recently went through the process of re-flagging my vessel to a new country and, as part of that, had to change the MMSI number on my Raymarine 650 AIS transceiver. I’ve seen some confusion and questions about this online, so I wanted to share the correct, legal, and safe procedure for doing this.

It’s critical to understand that changing your MMSI is not a simple technical hack—it’s a formal legal requirement when your vessel’s registration changes. Doing it incorrectly is illegal and can seriously compromise your safety and the safety of others. This post outlines the right way to do it.

Why You MUST Change Your MMSI When Re-flagging

An MMSI (Maritime Mobile Service Identity) is more than just a number; it’s your vessel’s unique digital fingerprint. The first three digits (the MID) specify the country that issued it.

  • Example: An MMSI starting with 338 is a US vessel (FCC issued), while one starting with 311 is from the Bahamas.

  • The Law: It is a violation of international regulations (ITU/IMO) and national laws to broadcast an MMSI with an MID that does not match your vessel’s current flag state. If your boat is now registered in Country X, it must transmit an MMSI issued by Country X.

  • Safety: Your MMSI is directly linked to your vessel’s details in your flag state’s search and rescue database. If you send a DSC distress call, authorities need to see your correct vessel name, description, and emergency contacts immediately. A wrong MMSI creates dangerous confusion and delays rescue efforts.

  • The Correct Legal Sequence 

    The most important part of this process happens before you ever touch your AIS unit.

    Step 1: De-register Your Old MMSI
    Once your re-flagging is finalized, contact the authority that issued your original MMSI (e.g., the FCC for the US, OFCOM for the UK). Inform them that you have re-flagged your vessel and request that they deactivate your old MMSI in the international database. This prevents “ghost” entries and ensures no two vessels will ever use the same number.

    Step 2: Obtain Your NEW MMSI from Your New Flag State
    As part of the vessel registration process with your new country, you will apply for and be issued a new, official MMSI number. This is typically done through the national maritime administration or communications agency. Do not proceed until you have this new number in hand.

    Step 3: Program the NEW MMSI into Your AIS Transceiver
    Only after completing Steps 1 and 2 should you program the new, legally-assigned number into your equipment.

    Technical Guide: Programming the Raymarine 650 AIS

    (Disclaimer: This is a general guide. It is your responsibility to ensure you are programming a legally assigned MMSI. Raymarine allows this function for legitimate purposes like this one.)

    • WARNING: The AIS transceiver must be powered down before you begin this process. Do not attempt to change the MMSI while the unit is active and transmitting.

    • First of all, you will need a terminal program – one that can send and receive text over a USB connection. For Windows, you can use Putty, or Tera Term. For Macs you can use CoolTerm, or Screen, or minicom.
      For Linux minicom and picocom are a few of many.
    • Regardless of which one you pick, you need to configure it for 38400 speed, 8 bit, No Parity settings.
    • Then while the AIS is off, plug in the USB to the front of the AIS tranceiver. Connect the other end to your computer.
    • Launch the terminal program and send these commands:

      $PSMT,0,3,0x2C75B2FA,1,nvdeli “mmsi”,52*45
      $PSMT,0,3,0x2C75B2FA,1,delay 100,53*06
      $PSMT,0,3,0x2C75B2FA,1,bootcmd 0,56*0B

      The first command does the job — clears the mmsi, the second line just waits a bit, and the third one reboots it.

    • Once it’s done, your MMSI should be cleared. Now to reprogram it: you need to download the ProAis2 from Raymarine’s web site
    • Once you have it downloaded and installed, launch it. Select the USB port, click Connect
    • The fields below should be blank. fill them out with your new CORRECT information, and then simply click Write Configuration.
    • The light on the device should eventually turn Green. You are all set..
    • Now turn on your Raymarine system and check to see if you can see yourself. Marine Traffic site does this for example. It might take half an hour to start seeing yourself there.

    A Final Critical Warning

    I feel compelled to state this clearly: Programming a false or unofficial MMSI is illegal, irresponsible, and extremely dangerous. It corrupts AIS data for everyone, creates a hazard for vessel traffic, and renders the global distress system useless for your vessel. The ability to change the MMSI exists for legitimate cases like re-flagging or replacing a faulty unit with the same MMSI. It is not a feature for spoofing or hiding your identity.

    Conclusion

    Re-flagging is a common part of international cruising, and updating your AIS is a key step. By following the proper legal sequence—deactivating the old number, obtaining a new one from the new flag state, and then programming it—you ensure you remain compliant and, most importantly, safe on the water.

    I hope this guide is helpful. Safe travels!