When I said "welcome aboard" there was no pun intended, but now there is. If you click on the link I posted and watch the video, you will hear David on board his house boat telling the interviewer that he can't get his sound that he gets on stage in the little boat cabin. But, then he switches from his blue Strat to his black Strat, hauls out a Fender Tweed and his distortion pedal and says he'll give you kind of an idea of his sound. Paraphrasing: You've got to have distortion and when he's on stage he can lean back against his wall of sound and get his inspiration, and he loves his Strat, etc...
It's true that you have to have technique in order to get his sound and it's also true that you will never capture it on a boat, on a stage or in a bedroom and especially on an acoustic guitar no matter how much you practice...but don't be discourged, continue your quest and think about using a Strat, a Fender amp and some distortion for starters. Get an teacher that is also into Gilmour and cop some licks!
http://www.youtube.com/watch?v=xPL3O7NmgpI <---- here's an on stage acoustic version, in case you want to try the acoustic route (a little harder on the finger bends for capturing his sound)...some of the electric sounds in the boat cabin are not that great, but it's a good place to begin and even David says [HE] doesn't sound like David in the cabin. It's always good to check out a performers' equipment and discography that you want to emulate (ie. Benson, Gilmour, Atkins, Knofler, Beck, Taylor, Emmanuel, BB, Guy, Stevie Ray, EVH, etc.)