I'm going to write a game and include simulated shipping based upon real data.
MarineTraffic.com has some great data, but I really don't need it to be live, up to the minute. I could use data that was captured a year ago or so, maybe hourly.
I've also looked at fleetmon.com and vesselfinder.com, but alas, they all want money. I've searched for a Google fusion table of maritime traffic, but no joy.
shipfinder.co looks interesting....
http://catalog.data.gov/dataset/commercial-vessel-density-october-2009-2010-ais-national might be what I want but when I follow the hyperlink to ftp://ftp.csc.noaa.gov/pub/MSP/AIS/CommercialVesselDensityOctober2009-2010National.zip it says "Page not found".
I found http://catalog.data.gov/dataset/2011-atlantic-vessel-density but it has a 500 meg .gdbtable file that I don't know how to interpret.