We've been on cool weather cruises and the ships are the same indoors as on Carib cruises. Actuallly a little warmer. Lots of women wear sleeveless on fall cruise and just like on the warm weather trips, they carry a wrap of some sort.

Now if you enjoy going on deck or on your balcony, then you need to have something warmer. But yep, spaghetti straps will be seen. Wear whatever you would to an indoor function.