Is there someone making these questions up for a la.
You may laugh but YES!
We were on the Maasdam earlier this year and the staff told us that they had just done a 10 day nudist cruise. On researching this on the web, out of curiousity, I found a company that specialises in doing this type of thing and they book several large ships every year.
I would take a blindfold if I were you.
I think that Royal Caribbean and Celebrity allow topless sun-bathing on the top deck. Ring them to check and if you are going anyway check in the daily ship's newspaper.
Topless is not the SAME as nude! Yes there is the occasional Nude-Cruise, check the net.
Yes it is the Luxurious ms Europa they have a nude deck the company is Hapag Lloyd. A mix of english,german,italian and american passengers. Its voted to the best luxurious ship in the world and extremly expensive but worth every penny.