I think that the "rank" of "Captain" is sometimes getting confused with the "position" of "Captain" and that there is no disrespect meant to those who hold the "Rank" of "Captain" when one calls someone who commands a vessel "Captain". After all, there are 'Captains " in all kinds of endeavors whether it be sports (captain of the team) or even in resteuarnts where there may be a captain of waiters/waitresses. One can be the "Captain" of the debate club or of a spelling bee. And as pointed out, Captain has differing legal meaning as when the person in charge of a vessel is the "Captain" but also where a person might be a legally, qualified(licensed) "Captain"
That being said, I think it is just a matter of personal respect and custom to address the commander of the vessel as 'Captain" irrespective of sex, rank, or license. and anyone who looses sleep over it or refuses to join a yacht club, or whatever, is being a bit thin skinned, and petty and may even be missing out on some good company and fun. I'd like to add that this dosn't mean I don't understand where they are coming from, but that I think that viewpoint is just a bit narrow.
Anyway, I think skipper works just fine for me
. Now about this calling girlfriends and spouses "Admiral"....