Which is the trouble with "boat"; the vowel sound there starts out as one thing after the 'b', and ends up as something else just before the 't'.
So, in *that* respect, das German "Boot" is more like the English "boot", where you also have the same single vowel sound all the way -- only trouble is, it's not the *same* sound; the English 'oo' in "boot" sounds much more "sissy". (Because it is pronounced farther to the front of your mouth, I think.) The German one is "deeper" or "darker" or... Ah, fuck knows how to express this shit in words.
All in all, though, I'd say the closest you can get to das German "Boot" in written English is "bawt"; i.e, the word "awe" sandwiched in between a 'b' and a 't'. (Where, in a charming display of the logic and consistency of English spelling, the two letters 'a' and 'w' denote a single sound.)
HTH!