From friends and family in the navy: whenever you see a fleet or battle group "stationed" somewhere, it means they are basically doing right turns in the middle of the ocean (a joke being that someone has to balance the effect of all those left turning NASCAR races). While they are doing operations etc, a lot of this time is considered extremely boring, more so than even long voyages going somewhere. Further, they usually aren't going full speed, so to some extent they are "just sitting there", particularly in the effect that they aren't using the full output of their power systems - leaving lots of power and (if needed people time) available for fuel "creation".