We went on a cruise last year around May, on Carnival to be more specific. At the time I only had the
P4 and did not think to bring it because I thought it was too bulky. When we got to the port there was a guy standing in line in front of us with a Phantom in his back pack. When we got to the x-ray scanner security officials confiscated his drone, told him that drones are not allowed in cruise ships. Told him that he would not be getting his drone until the last day of the cruise. This guy was pissed, told them that he had called the office and was told he could bring the drone. The security guy asked for something in writing, which he didn't have. He never saw his drone until the last day of the cruise.
I am platinum member in Carnival and Platinum with Princess. We stopped cruising when we saw this policy in cruise ships. We still go on trips but do not cruise anymore.
From Carnival's Web site: "The following items are prohibited and their possession is not allowed on board any Company ship by passengers or crew without a valid lawful reason, unless required in direct support of ship operations, as part of a crew member's official duties, and only with consent of the Ship's Master".
Here is a link to Carnival's web site prohibited items. Towards the bottom specifically talks about drones:
Carnival Corporation Prohibited Items | Carnival Cruise Lines
You may be okay bringing the drone, but there is no guarantee. I would start making phone calls now and if possible I would get something in writing. I would not just take their word for it.
Remember, once you are the Port they have you.