On a 15 day cruise, there's 3 formal nights ... first one is probably the Captain's welcome party ... last one the Captain's farewell dinner, BUT what's the third one for and when would that be held during the cruise - about midway or what? Thanks.
Traditional cruises typically have one formal night per week (or fraction thereof) in addition to a formal night for the Captain's "welcome aboard" cocktail party. Princess actually does not hold a "Captain's Farewell Dinner" though there usually is a "Captain's Gala Dinner" on one of the formal nights.
The other reality is that cruises longer than a week usually draw a very high proportion of repeat passengers. Thus, Princess's ships often must hold "Captain's Circle" cocktail parties on two separate evenings in order to accommodate all the "members" (repoeat passengers) on longer cruises. The "Captain's Circle" cocktail parties usually do occur on formal nights that might not have any special significance for passengers on their first Princess cruise.