Where the Ships Are: AIS and MMSI

You never know where the tangents will take you. My cruise ship schedule experiments began when a newspaper ad led me to a not-helpful-enough web page and, in learning about cruise ships and how and where they move around, I learned a lot that I hadn’t planned on learning.

Like about the Automatic Identification System (AIS), for example, wherein ships of a certain size broadcast digital information about themselves, in the clear, over VHF frequencies. Using a decentralized network of AIS receivers, websites like Google Maps APRS, Vessel Finder, AIS Hub, MarineTraffic.com, VesselTracker.com that aggregate ship position information onto maps and other feeds. It’s an interesting example of data that needs to be free and open — it’s primarily intended as collision avoidance data — can be shared in unanticipated ways.

One of the important components of the AIS system is the MMSI — Maritime Mobile Service Identity — which is a 9-digit unique identifier assigned to each vessel. Not only is a ship’s MMSI broadcast as part of its AIS data, but it it’s also used to allow voice and data connections to vessels. 

If you know a vessel’s MMSI, and you’re set up to monitor AIS broadcasts in your area, you can tell when a vessel comes into range.

I added the MMSI to the XML data file of cruise ships coming into Charlottetown this year — Maasdam, which arrives tomorrow, has an MMSI of 244958000, for example. If you Google that number you can find all manner of interesting information about the ship, from myriad photos (there is, apparently, an entire sub-hobby called “ship-spotting”) to its current position.

One can imagine — or at least I can imagine — an interesting hack that would monitor AIS data for Charlottetown and when a cruise ship was about to dock would sound some sort of klaxon to alert we citizens that the streets would soon be fully of horses pulling wagons, double decker buses, and rove bands of costumed fathers and mothers of Confederation.