Sorry but as you have not named a cruise line it's difficult to answer without quoting the rules & reg's for every single cruise line on the water, but as a generic answer, less & less lines allow it & the rules are constantly changing......Wilba.
Have a look at this website http://www.cruisegiftstore.com/feature_articles_archive7.htm.
Just come back from a RCI cruise to the Caribbean, RCI let me smoke on my balcony and they had loads of bars where I could smoke. Do not smoke a lot, but need a ciggie with my morning coffee!!