Up and down.
Jack insists that Rose get on a lifeboat as the ship sinks and Jack and Rose fight their way to the upper deck. He’s so insistent that she agrees to take a seat in one of the boats, but she turns her back after seeing Jack up on the deck and realising she might never see him again. The boat appears to have sunk about 10 feet below where it began when they lower it. The camera then cuts to Jack and Cal talking for roughly 40 seconds. The next time we see Rose on the boat, she’s only about 5 feet below, despite the fact that the crew kept lowering the boat as they talked. That is illogical!