Most early Oregon drift boats were made from 4'x16' foot side panels. They were roughly 14' 9" inches long with a 48" inch bottom and a vaguely 6' foot beam. Most of those boats were expected to carry three people at most: one rower and two passengers. The passengers, moreover, were expected to sit side-by-side on the front seat with no one behind the rower. That seating arrangement squeezes the payload as close to the center of the boat--to the boat's center of gravity--as possible. That makes the boat more side to side stable, easier to slow down and quicker to turn. That's hard to argue with.
If stability and nimble performance are the primary goals, seating should revolve around squeezing the payload as close to the center of the boat as possible. If your mind's eye imagines a blueprint line connecting the heads of two passengers up front with the head of one rower behind you will see a triangle, from a plan view looking down from above. The leanest, most efficient way to accommodate that triangular payload would not be a symmetrical hull. Most early Oregon-style drift boats are a bit wider up front and narrower behind, so both ends of the rockered bottom rise up out of the water equally, even though the weight was not distributed evenly.
Fly fishing from a moving drift boat changes the weight distribution requirements. Two passengers simultaneously back-casting fly line have to be separated as far as possible, so their lines do not tangle. One passenger goes as far forward as possible while the other goes as far back as possible. The old Oregon boats do not work well that way. They do not have enough bottom width at the upstream end of the boat to hold up a rear passenger. Fly fishing boats need to be symmetrical on bottom, with equal buoyancy at both ends, so they still trim properly.
Fly fishing boats do not perform as well. Weight out at the ends makes them side to side tippy and far slower to turn. They do row better than Oregon boats however, if the Oregon boats are forced to take a rear-seated passenger. Traditional Oregon boats are the most stable, most nimble boats out there, if and only if they are used as they were originally intended. If you do want to use a boat for carrying two simultaneous fly fishing passengers, then you need to make structural changes. Then you do need a symmetrical bottom.
Most Grand Canyon dories are evolved from an extra long and extra narrow boat designed by Jerry Briggs. The Briggs is a venerable white water warrior, responsible for thousands of hours of river running in the hands of top-of-the-line rowers. Most Briggs boats carry their passengers fore and aft fly fishing style however. It isn't a good choice. Briggs boats would be more stable and more nimble if they were a bit wider and if they squeezed their payload into the center of the boat, rather than spreading it out to the ends.
This is a 20' foot six passenger white water bus.
Most white water boats are decked instead of open. Mostly decked anyway. I got interested in big water boats late in life. I can't claim expertise a a white water person. I do have a lifetime's experience designing building and rowing dories in general. I do like decked boats. If I was younger I would be building decked fishing boats as well as decked white water boats. Decked fishing boats look like the smart and inevitable future to me. A decked fishing boat could have lower sides, so it would not be a wind sail. Lower sides are easier to get onto and off of, and they they are capable of far bigger water, when the need arises. I have crashed huge waves with my little 9' foot Dayak, which rides almost flush with the water surrounding it. Waves and water wash right over and are gone instantly. On a decked boat you can walk around as you wish, at least on flat water, which is what fishing boats spend most of their lives negotiating.
The Derald Stewart Canonita shown here and the more common Briggs boats are relatively long and narrow. Briggs boats are built with roughly 19' foot side panels but still with 48" inch bottoms. I think one well known builder has bumped that bottom width up to 51" inches. I'm building a decked boat now, in 2023, that features 18' foot 9" inch side panels and a 66" inch bottom. I can't say much about it yet because it isn't even done yet, let along rowed.
Hull shape (the length/width radio, rocker profile and side flare) and weight distribution are the most important white water design issues. Derald Stewart's great boats, the venerable Briggs and the historically interesting Susie Two (I have rowed one) all put the rower smack in the middle of the boat with two passengers all the way up front and two behind. I know from fly fishing boats that is not the best arrangement for high performance. Oregon fishing boats work better when you slide the rower back 18" inches or so and then put the two passengers side by side slightly forward of the middle.
I'm building a 17' foot boat primarily for three passengers not four. I'll put all three passengers side by side, in an extra-wide boat, slightly forward of middle, with the rower 18" inches or so back of dead middle. I expect that to make a boat far less side to side tippy and quite a bit faster to turn too. I started this boat in 1919 and got smacked hard by Covid--like a pallet of bricks falling off a crane--in March of the following year. I'm still not up to speed yet. I will get this boat row-able before the end of Summer 2023. Time will tell.
A.J. DeRosa in Jackson Hole has at least one huge boat designed by Cyrus Happy (pictured above) of Ray Heater's River Dories, built with 20' foot side panels and a 69" inch bottom. That boat is a bit like a big river Greyhound Bus. Cyrus designed it for large multi-day trips on the Deschutes. I have rowed that boat. It is amazingly fast and nimble, at least when not fully loaded. Cyrus's boat has two rows of three across in front of a rear-positioned rower. The proof is in the pudding. That boat does row better than a Briggs. A lot better. I am not in anyway denigrating the Briggs. It is a wonderful boat that has crashed a thousand waves, and has put smiles on thousands of faces. But the Cyrus Happy boat is a better performer. Anyone who has rowed both would quickly agree. The Cyrus Happy boats I have seen were all built as open boats. As a decked boat it would be a Grand Canyon master champion.