One of the couples on our trip down the Grand Canyon, Jonny and Marielle, rowed a 14 foot boat, while everyone else rowed standard Grand Canyon 18 footers (rented from Pro in Flagstaff). We were all pretty sure they would flip the boat at some point, including them. But they did a great job. They hit some big holes and massive waves, but never flipped. Here are some great videos from a nice HD cam setup that Jonny had: