They abandoned a perfectly good capsized boat!
SPOILERS!
I just couldn't take this movie seriously after they abandoned the boat. It didn't appear to be sinking, and they didn't discuss it to much length. A scene where they establish that all the food and rations are ruined or gone and that there is no safety gear in the boat would have made the abandonment of the boat more believable to me, but as it stands, they just swam out into the middle of the ocean as if that were the better option.
Anyone who has spent much time on the water knows that it is virtually impossible to keep your bearings without a compass or a landmark. There was scene after scene of the 4 people treading water, turning around, looking underwater, and then continuing on in some specific direction as if they were following a trail. They would have been so lost and way off course. An amusing ending would have been if the survivors found the the sailboat, still floating, instead of the island!