You're right. The ship, if it exists, is probably full of hot air. A highjacked empty ship opens all sorts of possibilities, though.
FYI: A British "tonne" weighs slightly more than an American "ton". Type each word into google web search for specifics.
Depends on the type of fuel. A metric ton of diesel would be 312 US gallons. Black oil, like Number 6 fuel oil, would be 271 US gallons to the metric ton.