Not APRS, but Automatic Identification System (AIS). It broadcast on VHF-FM marine radios channels 87 and 88. AIS is tied into the vessel’s GPS to show the current position. Way more on AIS then we can cover in this forum and more information can be found online by googling this term.
I think the first post is talking about this site http://aprs.fi/ It displays on the Google map.
the AIS info for the above site comes from MarineTraffic.com