Depends on what ship, what time of year, the cruise itself and what YOU want to do. My husband has done it both ways. He fought having to wear a tux for YEARS and finally 'gave in' 2 months ago. We also had our two sons, ages 14 & 11 yrs., in them too. Now I can't get him to NOT wear a tux!
check out this link:
<http://www.cruiselineformal.com>