The shorts and tops are fine during the day on or off the ship. Check daily to see what the dress code is for that specific night, a sun dress would be fine for "casual" nights, but would need something a little more dressy for the "formal" nights. This information will be printed in the daily cruise compass that you will get every evening.
sailed on the empress..we dressed up for dinner every night...on formal nite my husband rented a tux and i wore a gown..it made the cruise so much more special..
We were told not to underdress in bermuda...the locals don't want to see to much skin.
Have a great time...its the only way to travel...