Translation:I have a friend whose father is captain of a big ship.
In French which definitely uses the BANGS thing, there are some that go before or after, and have slightly different meanings depending on which way it is. He is a big man or he is a great man for example. And no, at this precise moment I can't remember which way round it is.
In Spanish, "un gran hombre" = "a great man" and "un hombre grande" = "a big man." It's similar with the French "un grand homme" and "un homme grand."
For some other adjectives in which position determines meaning, see https://www.thoughtco.com/fickle-french-adjectives-1368793 .
In a sentence like this "whose" acts as a relative pronoun linking the principal clause to the subordinate clause and I think that in Italian this is done with pronoun + cui.
When just using "whose" as an interrogative determiner before a noun (as in "whose umbrella is this?") then I think that the Italian is di chi.
Usually if "the" is used instead of "a/an" or vice versa you're going to be marked wrong. It's especially frustrating when writing down what's being said, since the person speaking or maybe it's just the quality of the recording make it very hard to distinguish between the two. Maddening, more than frustrating.
anaeastman: I think it's probably because 'vessel' is too broad in that it can include any object that holds/contains something and is not restricted to water craft: it could e.g. refer to an airship as well. "Ship" or "boat" are simply more specific and I'd say much more common.
CameronNed: Yes, generally speaking a ship is larger than a boat. We speak, e.g. about a "rowboat" not a "rowship" and a "battleship" not a "battleboat". Or a "speedboat" not a "speedship". Finally, there are 'steamboats" found on rivers such as the Mississippi and 'steamships' found on the high seas..
It is not incorrect to say THE captain, in context, because what the hell kind of ship has two captains. I know that the hyper-literal translation doesn't say "the captain of", but think how many times Italian does include THE where it ISN'T required in translation.