we have a plane to catch on December 18th in Koh Samui at 3 o'clock in the afternoon, we would like to spend the night before in Koh Phangan since it is full moon, so we would leave Koh Phangan in the morning to catch our flight in Koh Samui in the afternoon. Is that safe to do ? Do the ferries always run ? Is there an alternative (private boat ?) if ferries are full or not running ?