"There was a doctor on the boat."
Translation:Det fanns en läkare på båten.
If "det fanns" indicates a permanent location and "var" something more movable and temporary, how does this work for a person on a boat? As a passenger: permanent (at least until the trip is over) or temporary (from the point of the boat and the crew). Or perhaps a cruise line with en läkare on staff as a permanent position?
"där" mean "there", as in location, not "there" as in "there is". "Det" is an impersonal pronoun, equivalent to "it", in other words, a subject pronoun. For this reason, we need "det" before "fanns". In Swedish, a verb requires a subject in a sentence, and "det" is the subject in this sentence. I hope this helps.