11'8" is the universal cut off. the laws of physics dictate that two individuals weighing more than their equally divided masses will collapse into the center of the raft creating a singularity from which nothing will escape. if, however, the two individuals add an additional mass that exceeds their duplicated masses then the singularity will revert back on itself and undo the previous doing and blow up. there's an equation to prove this but my computer lacks the functionally to illustrate my theorem. suffice it to say that if joe says no, then don't go.