I don't really consider 'Black Friday' cruise deals actual deals. You see, most businesses create Black Friday savings by producing in bulk, knowing the consumer demand will be there in those dates. But, there is really no such opportunity for cruise lines - they can maybe discount some slow-moving excursions/packages or a last-minute sailing, but that's pretty much it.
The best time to find cruise deals is in the first 3 or 4 months of the year when everyone is tapped out after their holiday spending - while the cruise lines still need the cash deposits to continue trickling in.