I can't remember what it came to for Seatern but it did seem remarkably large. As Rob says, it's a measure of cargo carrying capacity and if I put that much cargo in Seatern, Matt really would pull his hair out... nor do I think Seatern would float!
Yesterday, on a whim while sailing near Calshot, I looked for Seatern's AIS report on the "Marine Traffic" web site. I recognised her immediately as the extremely small ship symbol surrounded by very much larger ship symbols! A bit like the VHF licence, when you register an AIS you have to put in your ship dimensions and explain exactly where the AIS antenna is located on your ship. I suppose for a large container ship you could be in collision with the bow some distance before the reported AIS position reached where you are! For Seatern the exact position of the antenna seemed slightly irrelevant... However I was amused to confirm that I could find my position by going on line - beats looking at your surroundings!
Peter