We've also been on the Liberty as well as many other RCCL ships and as with Dave, I wear dockers and golf shirts most of the time. On formal night, I'll wear a tie, but usually don't take a jacket. First, it's too heavy in the suitcase, but when I do take one, I almost always end up taking it off because I get too hot. And since I hate wearing a suit, if I do have to take one because of a special dinner arrangement, I'm only in it for a couple of hours. Just doesn't make since for me to take one, but it's what makes you feel comfortable that's important.
You'll see a bit of everything, so you can feel comfortable with a jacket and tie, jacket with no tie, or tie with no jacket.