Ok, if you're looking to buy your first raft or just interested in learning about the types of whitewater rafts, here's the deal. Modern white water rafts come in two basic flavors: 'self bailers' and 'catarafts'. Self bailers have the traditional raft shape, and catarafts, known as 'cats' for short, are made of a pair of pontoons straddled by a metal frame.
Self Bailers
So how can a whitewater raft bail water out of itself? Well, an ingeniously simple design makes it happen. You see, the floor of a self bailing raft is a wide flat inflated chamber, sort of like a big air-mattress. The edges of the floor are stitched or laced to the rest of the raft. When inflated, the floor is about 4 or 5 inches thick, so the top surface of the floor floats above the surface of the water. When water splashes into the boat, it flows across the floor, down over the edge, and out through the lacing. This design works amazingly well. A self bailer filled to the brim with water will proceed to empty itself in just a few seconds.
If you've ever bailed water out of a raft, you know how sweet it is to have a self bailer. In fact, if you float with someone who has an older non-self-bailing raft (known as a 'bucket boat' for the obvious trait - it retains water), you get to stop and wait for them to bail at the bottom of each major rapid. So, nowadays, when someone says 'raft', they are usually talking about a self bailer. If they say they've got a 'bucket boat', well, too bad for them.
Self bailers are the work horses on a raft trip because they can carry a lot of gear and passengers. Popular sizes are from 13 - 18 feet long, with 14 feet probably a minimum for carrying the gear and two adults on a multi-day raft trip. 15-16 feet is ideal, and 18 footers are nice to have on larger rivers. From a performance standpoint, rowing a self bailer is more like driving a bus. So the longer the raft, the slower it is to maneuver. And the performance of any raft is diminished if it is overloaded, pressing it deeper into the water.
Catarafts
Cats are far more maneuverable than a self bailer but carry less weight. They are the sports cars of the river. And like sports cars, they carry fewer passengers, but provide a lot of fun for the driver. If you're new to rafting, you would be well advised to consider buying a cataraft as your first raft. Their maneuverability will help you recover when you misjudge a rapid, and of course they are a lot of fun. If you live near enough to a white water river so that you can go boating on the weekend, a cataraft is the ideal raft for a day trip. And cats are also ideal for high water or extreme multi-day trips when each participant will row their own raft. Sizes of catarafts are described as pairs of dimensions separated by "X", like "12X20", "16X24". The first number is the length in feet, and the second number is the diameter of the pontoons in inches.
Paddle Rafts
Self bailers can be set up with a rigid metal (or on rare occasions, wood) frame that rests across the top of the raft, to which oar locks are mounted and oars attached. The other configuration is to leave the frame and oars at home and just use paddles. So the term 'paddle raft' refers to this other set up. It's just a term for a self bailer that is set up with inflated seats known as 'thwarts' (say 'wort' and add the "th") for passengers to sit on. Passengers are obligated to row, or more accurately, paddle the boat down the river. While this means work for the passengers, it makes for a very entertaining, social (and usually wet) ride! Most commercial river guide services run paddle boats to give the paying clients the full immersion (pun intended) experience.
The normal configuration for a paddle boat is to have a 'captain' (meaning skilled and knowledgeable guide) sitting at the rear of the boat shouting orders to the crew and using her paddle to steer or make fine adjustments to speed and direction. The 'crew' is the rest of the passengers, with half of them paddling on one side and the other half paddling on the other.
Boat Speed
Most of the paddle strokes that a paddle raft crew takes to steer the boat propel the boat forward. Therefore paddle boats move down the river faster than other boats. Self bailers are next fastest. Fully loaded self bailers carry a lot of momentum and offer a lot of surface area to the river. So friction with the water causes them to be dragged along easily by the current. Since it is a lot more work to fight against these factors, the steering strokes that the person at oars takes are usually forward strokes. The boatman just tries to adjust the direction or vector of the boats natural movement down the river. It may be surprising to know that catarafts are usually the slowest at travelling down the river as they offer less surface area for friction and are so light that it is easy for the oarsman to pull back, arresting the momentum. For these reasons, rookie oarsmen in catarafts are usually at the back of any group of rafts.
R2
You might hear the term "R2" mentioned in the context of whitewater rafting. This refers to a paddle raft being paddled by just two persons. They usually sit shoulder to shoulder in the middle of the boat, each padding a side. Of course, they can sit anywhere they want. The term R2 implies a sportier version of paddle rafting since it is more challenging to maneuver the boat when there are just two persons aboard.
Kayaks
Other forms of river craft are worth mentioning. The obvious one is kayaks. These also come in two flavors; hard shelled kayaks made of various rigid plastics, and 'inflatable' kayaks, also known as "IK's" that are made of the same materials as rafts. Both types of kayaks are a lot of fun and have their vocal advocates. I'll just point out a little bit of trivia. That is, while both groups share the river, hard shelled kayakers and rafters generally don't intermingle much. They are two different sports that share the same playing field. But some hard shell kayakers shun their inflatable brethren in IKs. So, ironically, inflatable kayakers tend to hang out with the rafters. I guess it's a case of 'rubber sticks together'.
J-Rigs and Sweep Boats
Finally, you may come across two other types of rafts. 'J-rigs' are giant rafts that are very specialized passenger and gear haulers. J-rigs are constructed of huge pontoons and are often motorized. They're used by many of the commercial rafting companies in the Grand Canyon. Sweep boats are named for the two huge oars used to steer them. They are basically very large self bailers, but the oars extend out both ends of the craft, and steer the boat like rudders rather than extending out the sides to row as a normal self bailer does. Sweep boats (or "sweeps") are commonly used by commercial outfitters on the Middle Fork of the Salmon (you'll rarely see them on other rivers). Their advantage is that they carry huge loads of camping gear and food. And, due to the huge displacement and surface area exposed to the current, they are the fastest non-motorized craft on the river. Their disadvantage is that they have no brakes! Trust that if you see one, the guide holding those big oars is both very courageous and very skilled!
