In fallout 3-Point lookout How do you get the key to the engine room on the boat if there is 1?

Well, there are two ways to go about doing this.

1.) Right off the bat, you can kill the boat captain and steal the key, but I don't recommend this, as it messes up the story arc.

2.) Complete the main storyline in Point Lookout. When you finish and head back to the boat, the girl will be waiting, telling you that the captain is in the engine room. You then enter the room and kill him. But be prepared. It's kind of freaky in there...