Just finishing this, and missing one letter- and I'm sure I'll feel even denser when I find out what it is. For 13a: Small boat that lacks e.g. boater to paddle (4) I have TRO_. I'm assuming it's trog, and that there's some word for boat that you can drop, say, hat from to get it. Aaaaaargh. Also, I have INMATE for 6d: One doing time, not available set apart inside, but don't get the wordplay. Ditto sound of frustration.