The three-raft rig hits the boil and disappears then is flung upwards and crashes against the cliff just below my feet. No tubes break, no frames bend, and they are able to go on downstream. The whole river is breaking over a large boulder in midstream, raising a 15' high boil in the center of the river. Unavoidable. Yippee. The drop here was about 15 feet through the chute.