Excuse me, but that is not possible, or at least wasn't until recent cruises. We frequently have been forced to relenquish our passports (Canadians and other 'foreigners') to the ship's authority. Supposedly dependent on the ports visited. Americans loved to tell us this was for our own security "you wouldn't want to lose something as important as a passport!"
But apparently Americans could be trusted with theirs. I always thought this was downright illegal as it says right on the passport not to let it out of your possession. I don't know if this is still being done or not. Most ports ie. Caribbean or Mexico, I will use only a photocopy of passport. Perhaps when I visit Turkey, Asia etc. I will take the original. I think it is more secure in the safe than in a beach bag!