When we were on Carnival Spirit we had two formal nites and no Semi Formal nites. Made my hubby real happy not to have to wear a tie and jacket other than formal. This was on a 16 day cruise so I would think that on a 7 day, there would be no semi formal nite. Nice pants and shirt should be fine.
Is there a description of casual, semi-formal, and formal in your cruise brochure? Check it out. We, who answer, may be the scuzzies that sat at your table last time in jeans and shorts. Maybe a pair of overalls with a crease down the leg is formal!?!