Japanese 1 The annoyance of "oo"

Is Shachoo spelled しゃちょお or しゃちょう? I was under the impression that if two "oo"s where present I'd have to put a う at the end but apparently that is not always the case.

>>17
The "historical reasons" I mentioned, explains how things are spelled differently than they are nowadays pronounced. In the English example, "oo" once had uniform pronunciation in "foot"/"boot"/"poor".
Similarly, the Japanese articles "wa" and "o" are still being written "ha" and "wo" in kana, because that's how they were once pronounced. I imagine it's the same with the "ou" spelling of long o's.

Oh and btw, Romaji hardly sucks at all when ppl will just, like, actually follow the rules. (ちょお="chou", ちょう="choo", for starters. "Chō" is useful for showing pronunciation, especially to Anglophones still stumbling over how they pronounce things.)