In this context it's used as a metaphor for the back end or rear end of something. In this sentence it sounds like he's talking about a sinking ship, so this probably refers to the rear end of the ship (the technical English term for this is the "stern" of the ship). The ship is sinking and its rear part has lifted up into the air. Also, you should be aware that "ass" is a moderate profanity in English - it refers to someone's butt or rear end. So, be careful when you use it :) Some people might find it offensive, especially in formal or professional situations.

Additional notes: This is dialog from the movie "Titanic." It is spoken by a technical person, who's done a computer simulation to show what happened during the sinking. He's speaking colloquially, not quite slang. He's excited and intrigued by the technical puzzle. He's enthusiastic. He's impressed by the magnitude of what happened. He's also being irreverent. He's half-joking. He's being disrespectful about the great ship. He's almost enjoying it, as if it were a video game, although in reality it was a tragic event. At the end of it, Rose, who has lived through experience, says, with cold anger, "Thank you for that fine forensic analysis, Mr. Bodine. Of course, the experience of it was... somewhat different." This is probably in the movie as hidden exposition. Later on, moviemaker James Cameron is going to show us what happens to the people on the ship when that happens. The detail of the stern become elevated in that way is not a familiar part of the "Titanic" story (it might not even be true), and we need to have it explained to us so that we will know what is happening when we see it later on in the film.

I think this comedian sums it up nicely! https://www.facebook.com/teamcoco/?hc_ref=ARTV_mvxbafPlEsZ0gVIU4EBAEDbT7QYLcSUni8RW2CrEiP6nHJuJ6LJjqd9Csjq8GI&fref=nf