I lucked out and caught a Grand trip with Jack (Paco), who brought a Fat Cat and a Cutthroat. I paddled the Fat Cat most of the time and took four swims. The holes that got me would've dumped me in any
inflatable paddle boat. My fault for hitting them.
In big water, the major difference I notice between the Pack Cats and duckies is that the ducks fill up, which adds stability but makes them doggy and hard to manuever. Yeah, they are self-bailers but it takes time. And I don't like that bathtub feeling. By contrast the Pack Cat stays buoyant and will bounce (fly) off the crest of waves. Clumsy paddling or an upstream gust can knock you off line.
But, the load capacity, etc. aside, the main reason I love Fat Cats and Pack Cats is that they're by far the most comfortable duck-size craft available. The adjustable footbar and inflatable backrest let you change your body position on the water, and they're excellent for people with touchy backs.
Another great Pack Cat feature is that on flatwater reaches in viciously hot weather, you can ooze down between the tubes and float along mostly submerged, without ever getting out of the boat. It's good for fishing. You can put your feet down, stand up, and cast without leaving the boat. It's also a lifesaver for ducking under wire fences when running streams through ranch country. Peeing is easy, and unobtrusive.
Jack said the reverse cones on the back of Pack Cat tubes were to make it easier to self-rescue. But I never scrambled back on from the rear. If you can hang onto the boat and your paddle, in big waves, you can wait 'til the boat dips over the crest ahead and the roll back on from above. Slick!
My Cutthroat tubes are rigged wider (24" between) than the stock Jack's frame, and I prefer the wide rig for difficult water.
I have two 12" Pack Cats, and have used them in class 3-4, but if I bought a Fat Cat frame, I'd be happy using it with the 16" Cutthroat tubes. The major problem with these boats, paddling in big water, isn't the waterline length but the lack of power. Oars on a frame are much more powerful. I'm confident running the oarframe rig in water that would scare me in paddle mode.
But the oarframe + oars are too wide for creeks and bouldery streams like the Escalante (UT). That's where the Fat Cat & paddle are the ticket.
What's nice is that the same tubes will do fine for both the oarframe and a paddle setup.
Here's to Jack—