I agree with TYphoid about the hype and such, even the history channel has fallen prey to these bait and switch drama type shows, and I used to be a card carrying skeptic myself, but I tell you what, until you see something that you cannot explain to yourself, let alone anyone else, all the while telling yourself that, yeah, yer a reasonably smart person,,so why does this scare and humble the holy &@%$ outta me?, you just wont understand, and thats your right.
Concerning the methane bubbles, hard to say if that much gets released at any one time, but I saw a test in a tank on a reasonably large scale replica of an ore freighter, and it sunk like a rock, gotta remember, all those bubbles are displacing a lot of water that otherwise supports the ship,