Peter, this is question of phonetics which is must be a constant source of confusion for ESL students. The word is Hull with - as you rightly said - the 'ul' of culture. With an American accent this would turn to 'al', but it doesn't mean that the latter way is correct; just said with an accent! There are countless other examples but don't sweat too much about it. Suffice to say, the English pronunciation is original.