We came through a section of Class IVs (don't take this boat on Class IV's). The river mellowed into a retaining pool and then under a train bridge built on a ledge at an angle downstream to the right. All but two passages were covered in debris. My buddy chose the river right of the two and went first. The current created a pretty strong 'berm' off the bridge piling to his right meaning that the direction of the current changed backed to the left halfway under the bridge. The flow pushed him into the piling, on which one pontoon caught on the concrete while the other was pushed in the current beginning to spin him. He got nearly vertical and was at the literal tipping point when he got an oar on the piling and got a strong push off of it freeing himself.
Seeing this, I chose the passage river left of his. Once committed, about 15 feet from the bridge, I realized that a tree blocking the entire passage to my left actually extended across the entire passage I chose at about a foot underwater. The current was too strong to bail on this approach. Having been flipped by trees underwater before, I kind of knew what to expect, so I braced myself to be able to balance the boat. Because your ass sits so low on this boat, it displaces water differently than pontoons or other kayaks. When I hit the tree, all water at the obstacle was displaced and it felt like a solid 20' rail slide into the concrete piling. During the slide, I felt I could still ride it out, but the second the boat touched the piling it flipped (very violently) plastering my head into the piling.
Almost as instantly as the boat flipped, I was sucked underwater. The next thing I know, my face was being pushed into the base of the piling and I was pinned under debris underwater. Without panic, I worked hard to free myself from the debris, hit my head pretty hard on something and then somehow got free. The initial relief was instantly gone as I started somersaulting underwater bouncing off rocks and bottom as I went (couple bruises remain from that still). I was carried into a deep hole which allowed me to surface as I could use my fins to get my head above water. Yelled to my buddy who started after my boat, but was then sucked back down and started bouncing off rocks and bottom again. Went over another big boulder and had room to kick to surface again and was finally able to kick into a deep back eddy and get to the bank.