The cruise we took was in & out of Southampton, so a large number of Brits were on board which probably pushed up the number of Tux wearers as there wasn't any weight issues.
I would have to say that about 70 to 80% of the men who wore formal went for the Tux & BowTie, with about 20 to 30% in dark suit & dress tie. There were a few dozen who chose to wear neither, but they were definitely in the minority.
I hope this is of some (if little) help, I'll take a look back through some of our photo's this evening to check my memory of %'s.
On the subject of photo's, if you are interested, we've posted about 100 of them in the photo section
Alan & Katrina
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Then: P&O Oceana December 2016
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