The comedian on our cruise (a big guy) was joking that the quickest way he found to shower was to turn the water on, soap down the shower walls, get in and spin around..
But really, they are not THAT small. If you need a bigger shower, go up and use the spa/gym showers facilities. But one person at a time is not bad.
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, Celebrity Silhouette 2013