MMSI identity format
Aid to navigation MMSI (99MIDxxxx)
An MMSI in the form 99MIDxxxx identifies a aid to navigation. How to recognise it, where its country digits sit, and why reading the first three digits as a flag would be wrong.
What it identifies
A 99 prefix identifies an aid to navigation (AtoN): a buoy, beacon or lighthouse fitted with AIS, or a virtual AtoN that is broadcast from shore for a position where no physical mark exists — a new wreck, for example.
How to read it
An AtoN is a fixed mark, not a vessel. Virtual AtoNs have no object at all at the position shown, which is exactly why they are useful: authorities can mark a hazard before a physical buoy can be laid.
Does it give a flag?
Not a flag — the MID in digits 3 to 5 identifies the authority that operates the mark.
Every vessel page on this site works this out before printing a flag. Where the MMSI is not a ship station, the page names the kind of station instead — a wrong flag is worse than an honest “this is a coast station”.
All MMSI formats
| Pattern | Station |
|---|---|
| MIDxxxxxx | Ship station |
| 00MIDxxxx | Coast station |
| 0MIDxxxxx | Group of ships |
| 111MIDxxx | SAR aircraft |
| 99MIDxxxx | Aid to navigation |
| 98MIDxxxx | Craft associated with a parent ship |
| 970xxyyyy | AIS-SART (search and rescue transmitter) |
| 972xxyyyy | Man-overboard device |
| 974xxyyyy | EPIRB with AIS |
| 8MIDxxxxx | Handheld VHF with DSC and GNSS |
Have a number to check? The MMSI decoder applies these rules to any nine digits. For the background, read Reading an MMSI.