RedactedNarrative: O1 said that he was driving in a straight line at a low speed during the incident. He was operating the boat at a speed less than which his speedometer could read. V1 was sitting on the floor of an  inflatable towing tube.  V1 was sitting with his feet forward and his back resting on the thwart. O1 then said V1 rolled out of the tube on V1s own accord. No environmental or boat operation had persuade him to get out of the tube. V1 rolled over the side of the tube and into the water feet first. V1 was wearing a personal flotation devise and immediately started to scream that his Left shoulder hurt. O1 picked him up in his boat and brought him to the boat dock. victim and subject walked to the marina store where Ranger made contact with V1. V1 was transported via ambulance to CPMC.  V1 had complained of a previous shoulder injury and I was told he was set up to get shoulder surgery in the near future.