Ask Sail: Two AIS Numbers

I have a Boat U.S.-issued MMSI (Maritime Mobile Service Identity) number for my VHF radio, and now I’m adding a Garmin AIS 600 Class B transponder.
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Dean Lewis, Brunswick, Georgia

Q: I have a Boat U.S.-issued MMSI (Maritime Mobile Service Identity) number for my VHF radio, and now I’m adding a Garmin AIS 600 Class B transponder. Does it need a separate antenna, and can I use the same MMSI number that I received from Boat U.S.?

Gordon West Replies

A: Your AIS 600 from Garmin has a built-in antenna splitter. If your current VHF antenna is working well, this AIS unit can share the same antenna without any major loss of VHF performance. You should obtain an FCC marine station license with an FCC-issued MMSI number if you operate your AIS operation well offshore, or if you cruise north to Canada. You’ll then have two MMSI numbers for the same vessel, but as long as you keep your MMSI information up to date, your VHF and AIS transceivers will be properly identified. It would simplify things to have just one number, but your VHF will refuse to overwrite its existing number unless you have an NMEA marine electronics dealer reset its MMSI circuit.

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Photo courtesy of Garmin

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