There is more involved in embarkation than boarding the ship - such as setting up your onboard account - Carnival is not set up to do that. My one visit to Key West we docked at the Navy base, another ship was tendered off shore (don't remember which one). In either of those cases you might not even be able to get to the ship.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014