It appears the first US vessels have been approved to sail to Cuba.

http://www.passagemaker.com/articles/trawler-news/legal-affairs/u-s-approves-private-boats-to-cuba-for-first-time-since-2004/

Vice Commodore, OCC 

Tourism travel (e.g., by boat) is not specifically permitted as of this time (Jan 2015).

http://www.treasury.gov/…/sanctions/Programs/Pages/cuba.aspx
http://www.treasury.gov/…/Progr…/Documents/cuba_faqs_new.pdf

Vice Commodore, OCC