Just back from northern Europe on Century. Wore sweats on both days at sea. A perfect choice. Lightweight , warm, and comfortable. Glad I brought sweats along. I also like to wear them on the plane.
Informal and casual have seeemed to become the same. Men wore slacks and neat sportshirts. A few wore sportjackets... many did not wear a jacket. Formal has also become less dressy. Men still wore suits or tuxedos. Women wore everything. Most were not very formal. I wore a long knit black dress.. it wasn't exactly formal, but it was fine. I leave the very dressy formal clothes home.