I'm not really sure if they plan a set course for these cruises or not. It may depend on the weather as to which way and how far they go. Most likely they will cruise out into international waters and make very large circles very slowly and then come back.
Why does it matter how far they go? You will have a good time. Just remember that it will be a little different than a longer cruise in that you won't be stopping in any ports. So you will miss out on that part of the trip. But there will be plenty of other activities to keep you entertained.
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
NCL Dream October 2006, RCCL Mariner OTS June 2007