It appears that the rig jacknifed. That would be the only explanation for how the trailer could be bent in that fashion. Jacknifes occur when the tow vehicle is stopping but the towed load isn't. It pushes the rear of the tow vehicle out and around. Common accident with tractor-trailers. Odd with a boat- usually the trailer has enough brakes to keep the whole thing straight. A properly set up trailer braking system will actually assist the tow vehicle in stopping.