I wore a hat every day and it never flew off. It wasn't very windy though from what I remember. I think this question would also depend on how tight you wear your hats..
do you clip it to your hat and collar?
It really depends on how windy it is, and the type of hat you are wearing.I know that weather changes, but based on personal experience, hats on deck? will it fly into the ocean? My first cruise will be to Alaska if that makes any difference, but I plan to do more than one.