In most episodes, Gibbs in seen working on his boats in the basement. He gets a couple of them done, but it doesn't show how he gets them out of the basement.
Anybody know how he gets them out?
There has never been enough detail provided in the episodes that have aired to date - there are a few hints and a few jokes along the way (like knocking down a wall and using a ramp) - but this one doesn't really have an answer currently.
The boat "Diane" does have an answer as to what happened to it;
In the episode "Kill Ari" (3x02) Jen goes home with Gibbs so he can change clothes after being out in the rain storm, and sees the boat Diane. She asks if this was the same boat he was building 6 years ago to which Gibbs answers no.
When Jen asks what happened to the other one, Gibbs tells her that he burned the boat.
However, whether the boat was burned inside the house or not (unlikely, considering that burning a boat in a basement would probably burn the house down) is never covered in the show.
The accepted answer mentions conversation "like knocking down a wall and using a ramp." This dialog comes from season 3 episode 7 - Honor Code when Gibbs is taking care of Zach while his father is missing:
ZACH: Gibbs, can I ask you a question?
GIBBS: Yeah, shoot.
ZACH: How are you going to get this out of here when it’s finished?
GIBBS: Good question. I don’t know. I haven’t thought about it much.
ZACH: I think maybe you could use a crane or something.
GIBBS: Yeah? I could dig a ramp. Knock that wall out and hoist it out of here.
ZACH: I went sailing once with my dad and Commander Wilder. Didn’t go too well.
This is one of the few pieces of dialog in the series which discusses getting the boat out of the basement (I am watching the series from the beginning, so there may be other hints in future episodes). But it is unknown if Gibbs acted on this idea.