I guess you guys haven't seen the Mythbusters Titanic special. They proved if they were smart enough, both Rose and Jack could have feasibly stayed on the bed frame and both would have had equally high chances of surviving.
That episode demonstrates that they might feasibly have survived if they had had the time, capability, and knowledge of floatation dynamics to think about that. The Mythbusters team found a way to make it work in a lab scenario.
Exactly. It was a good episode but they "proved" nothing. A team of college engineering students also once determined that everyone on the ship could have survived if people had worked together to form a "ring" with the light boats and tied a bunch of the deck chairs, tables, and other floating devices together in the center of the ring. This would have created a large, massive, single flotation device that could have supported everyone on the ship. But, again, the problem with that is it requires dozens of people in a crisis situation to work together to formulate this plan to implement it and 1000s of people during this process to not panic.
The movie probably could've done a better job of establishing that the debris couldn't support both Jack and Rose (as it is they both seem to try and climb on it at the same time which simply causes it to tip over rather than sink under the weight.) But I've always maintained that they both simply couldn't be on it at the same time. Switching out on the debris wouldn't be practical nor likely to do any good as only minutes in the water would have been deadly.
The Mythbusters did nicely show that as shown in the movie the debris couldn't support two people at once (even if it was the right physical size) wood is buoyant but not THAT buoyant. Jamie and Adam were only able to get the debris to support both of them after modifying it by tying their lifebelts to the debris. Something that would have taken time (and thought) for Jack and Rose to do, something that likely didn't have going for them in arctic conditions in the early hours of the morning after having been running around for the last 2+ hours. (Not to mention not having the advantage of hindsight.)
I do "agree", though, that had Rose stayed on the lifeboat Jack may well have survived as he would have found the debris and gotten shelter on it while she was in the lifeboat, Jack then later would have been saved when the lifeboat came back for survivors. But then there's the question on whether or not he and Rose would have been able to reunite and live happily ever after or if Rose would have gotten drug away by Cal or her mom.
(We could also quibble, though, that if Rose stayed on the lifeboat then things might have been changed so much Jack may never have found the debris. Butterfly effect and all.)
But Jack was a third-class male passenger. The odds weren't in his favor to begin with.
