Daddy, the ship will adjust it's time to whatever time zone you are in at the time and re-adjust itself on the way back to port. The ship will notify passengers when the time shift does happen and the ship's clocks also change. It's seamless and I never notice the effect. So, to answer your question, no, the ship will not remain on EST.
Not always! We have been on many cruises out of Miami that stayed on eastern time for the whole cruise, even going on a western Caribbean. The ship will clearly inform passengers to remain on ship's time even though local time is different.
I think it is like Dave said.. Its the preference of the captain. I have been on Carnival ships that ship time is the time zone you boarded in and I have been on ships that change time. It may have to do with how many zones you cross. Maybe for one time zone they don't bother, but for more than one, it can be a problem with the port staff and they change it?
================================================== ========== Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013