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....