Your or your son is hitting something floating in the water . A piece of wood is all it takes. Go back to the dealer and get your old prop back as it is yours and repairable. I would also recomend you repair any prop and wear ring items yourself since its utterly simple . If you do hear something in the jetdrive SHUTDOWN immediately and tow to shore to pull the item out with a stick . Teach anyone who rides it this as well. If you drive any distance to where you ride I would also recomend getting a spare wear ring with the tools to replace it and keep them in the tow vehicle . For less than a hundred bucks this could save your weekend.
I would pull your housing off the back and be sure the driveshaft is not stripped.
I would pull your housing off the back and be sure the driveshaft is not stripped.