Richard -
Your post offers quite a bit to consider and you are to be thanked for all that you provided. May I just ask a couple of questions?
In the reports on this story, two boats have been mentioned in connection with the three women. One has been described as a 16-18 foot fiberglass trimaran runabout. The other was a 26-28 foot Trojan cabin cruiser. Some say the three girls first entered the smaller boat that had one man on it. Later, they are reported to have gone aboard the larger craft that had three men on it. There is a belief that they spent some time back on the beach in the time between being on the boats. I assume you mean the driver of the smaller boat may have been showing off at a high speed and flipped it. If that is the case, how could they have later been seen aboard the larger craft? Also, I can understand how one or even two bodies going into Lake Michigan may not be found, but what about six (three women and the reported three men)? I would also think there would be wreckage of some kind seen in the hours and even days after an accident.
The approximate weather in that area could be found by checking microfilm of area newspapers from that weekend. I tend to think it was warm weather (mid-70's up into the 80's) with sunny or partly sunny skies. Good enough for a number of people to be on the beach and in boats on that day.
There was a movie, according to case summary information, which showed that there were different two boats which were near the beach at two different time. However, it has never been conclusively proven that the girls were on both boats. It has been Speculated, but not proven.
In my previous post, I suggested that that film footage be analyzed to determine if, in fact, the three girls who boarded the smaller runabout were the same three girls seen on the Cabin Cruiser some hours later. They would probably be wearing the same swim suits on both boats. For that matter, can it be determined that the small boat operator was one of the men filmed on the larger boat?
There is a lot of conflicting information and witness testimony, but as the police indicated, they tended to believe the initial witnesses as most reliable. Those witnesses stated on the day that the girls disappeared that the girls left their stuff on the beach, swam out to and boarded the smaller craft, and NEVER RETURNED for their stuff. These first witnesses did NOT state that they saw the girls on the larger boat.
Several days later, someone else claimed to have seen the three girls ashore between alleged boat rides. Did that witness actually know the women? Did he actually see the same three women? And could he say positively (several days after the fact) that it was at say 2PM instead of 11 AM?
IF these women were murdered, it wouldn't make any sense to cruise around with them for several hours, parading them in front of so many witnesses on the beach. And IF there was some accident in the open water - out of sight of witnesses - it would more likely be in a fast moving surface skimmer than on a larger, more stable platform. If a small boat were to flip or collide with something, it would be more difficult to get out an emergency message than if a larger boat came into distress.
My point about the weather is that while it might be a nice day on the beach, the weather affects boating significantly if the waves are high or if there is rain or lightning. The rougher the weather and water, the more likely chance of a boating accident.
Knowing the weather, winds, currents, etc would have provided the Coast Guard with necessary information to search for possible victims - but they would have to know that there had been a boating accident before they would begin such a search. In fact, I think that any searching was conducted in and around the park itself.
In regard to a possible accident and missing persons, Lake Michigan is not a small body of water. There may have been a lot of boats near shore, but simply heading north away from the beach would quickly take a boat well out of the sight from shore or other boats.
Again, analyzing the film could provide significant clues toward solving this case. Every boat is required to display its registration numbers and letters on both sides of its bow, and knowing those numbers would allow an investigator to determine who owned the boat at the time - and every subsequent owner as well.