There were separate cabins on the Durmstrang ship for every year except seventh. Seventh years didn't get cabins. They navigated.
With supervision.
Usually.
"We're on course!" Anna snapped. "Merlin, you're such a sissy."
"How do you know?" Igor jabbed his wand at the mess of ever-changing coordinates on the magical map. "Who could possibly make sense of that?"
"I can, thank you," Lera said, "and she's right, we're doing fine. Besides, we can't be worse than last year's crew. Remember how Malinkov didn't tar that one cabin and it leaked?"
Igor did indeed remember that. It had been his cabin.