I have rowed several thousand miles in the original Riken Cheyenne. My raft was the prototype, hand made for Dan Baxter and Vladimir Kovalik who originally came up with the tapered-tube design back in the mid-1980s.
This very raft was featured on the cover of the Jan/Feb 1986 issue of River Runner Magazine, and the accompanying article says that the "diminishing tube design allows for significantly more interior space and . . . helps the boat slice through waves rather than stalling on top of them." The article also quotes Kovalik saying that the raft looks like a fat inflatable kayak, and explains the pointed ends this way: "In a reversal, the more pointed the boat, the better it punches through the wave."
The design was a direct outgrowth of the relatively new self-bailing raft idea, in that the tapered tubes would allow a lot more water to break over the front of the raft, and such a thing would be imponderable in a bucket boat. On my raft, the tubes tapered from 22 inches on the sides, down to 9 inches at the ends. The first production Cheyennes tapered only to 11 inches, and because the public thought even that was too radical, the dimension was increased again, to 15 inches, which is how most of the Cheyennes were built.
I met Vladimir (who spotted my raft and came over to ask how I liked it) during a trip down the Rogue River, and he told me that his idea was to make a raft that could do vertical or near vertical drops. That required a very sharp upturn in the floor, to keep the raft moving rather than stopping at the bottom of the drop. To get the maximum upturn on the bottom without changing the frontal profile, he tapered the tubes. The River Runner Magazine photo was taken at Hussom Falls on the White Salmon River, demonstrating how well the raft handles the near-vertical drop.
I personally never attempted anything like that, but I did find that the tapered design resisted stalling when run against big reversal waves, and it was far less affected by upstream winds. I considered both of these to be big advantages over conventional rafts. And I made full use of the extra load-carrying space in the raft. I liked the raft. I liked it a lot, and it was my primary personal raft for 25 years!
I now row a 16' Vanguard that has the same load capacity as the 15' Cheyenne, which I have given to my daughter, who rowed it down the Grand Canyon right behind me (shown here in Hells Canyon). In The Canyon, Cheyenne didn't perform as well as the more traditional rafts. The low bow allowed the massive waves to blast right over the boat. The V-Wave at Lava Falls blew my daughter right out of the raft. One other mishap occurred at Badger Creek Rapid, when she followed a less-experienced boater right over the pour-over boulder at the top of the rapid. The hole yawned as she went over, and going vertical, Cheyenne dived straight to the bottom. Then, like a kayaker doing an ender, the raft popped back up, the stern sailing downstream, and Cheyenne landed upside down. It was the damnedest think I've ever seen a raft do.
Still, on balance, I would have bought another tapered tube raft had I not run across such a great craigslist deal on my Vanguard. I love the Vanguard, but Cheyenne remains the best raft I've ever rowed.