Yes they are.
Eaglelord17, above, mentioned how he went on a Victoria and found it too tight to even call it small. Well, the Vics are cruise ships compared to the good ol' "O"-boats, and we didn't feel crowded in them old O-boats. It is a difficult concept to translate for people who don't know it: you learn to live within yourself .. in a crowded place, and let others live there too.
There is a reason why the CSA and NASA psychologist working on long duration human space flight study the psychology of submariners.