With great difficulty!! I never managed it! They say get the VIN/Chassis number then put it in a website to trace what boat it's on, but I could only trace VW's going to Australia, not a lot of help. If you can find out what boat it's on you can trace that across the water
The 2 sites I was given were:
http://www.vwwatercooled.org.au/forums/f40/new-vehicle-tracking-transit-33039.html(the clue is in the web address org.au)
http://www.marinetraffic.com/ais/shipdetails.aspx?mmsi=212204000
Use this site to track boat, when you know the name of it! This is a good site.GOOD LUCK