|One last possibility and the one that now makes the most sense to me. |
The owner was behind the helm by himself, confident that everything was going just fine, letting the crew sleep off the earlier partying. They had drinks in their hands in some of the photos. He purposely set the track for the North Coronado Island so that he could make a straight shot from there to Ensenada when nothing would get in the way. He probably figured out that they'd be getting close around 12:30-1:30 when he would alter the course and let someone else take over. With a slightly different tack, they might even pick up some wind.
At some point, he decides to relieve himself. As you can see from the earlier shot, there's not much to hang onto back there. He probably went to the corner because there were so many things on the back that would get in the way - outboard motor, BBQ. One little lurch of the boat could have sent him overboard. With the engine running, the guys below wouldn't have heard him. Could also explain why one of the bodies is still missing.
Whew, glad there's a couple of explanations. It was driving me nuts.