You probably should check with the airline you are flying for verification. This is the first time I have heard of a weight restriction for a carryone. 11lbs is not much. Most business trips my computer bag weighs more than that. The only restrictions I have heard on carry ons are that they must fit in the overhead bin or under the seat in front of you.
The cruise ship does not impose a weight restriction (other than it has to fit in your cabin) But again you should check with the airline you are flying with.
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
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013