There were three persons on a tube which was resting on the rear of the vessel on an angle extending down to the water and resting on the teak deck at the extreme rear of the vessel near the surface of the water.  The operator stated she was in reverse and traveling backwards when the tube suddenly lifted up and caused the three girls to fall from the tube into the water.  The victim who was in the middle of the tube fell straight into the water and was sucked under the boat and struck causing injury.  The other two girls swam uninjured swam to shore.  All the girls in the tube were wearing life jackets and there was a spotter on board.  
Littleton