The general shape of the hull has transformed from rounded to sharp edges. Bottoms have gone from slightly rounded to dead flat. Four attributes of whitewater boats are speed, maneuverability, acceleration, and performance or the ability of the boat to play in holes and surf waves. Speed is good if you have a long way to go in a day or you paddle a river with a lot of flat water. Maneuverability is needed to negotiate rock studded boulder gardens, tight drops, and to catch micro eddies.
Acceleration is very important to play boats.
Performance refers to the boat's ability to perform various maneuvers To accomplish any of this, the boat needs to be appropriately sized to fit you very well. Boat size is measured by volume, in gallons, and by paddler weight. The most important aspect of fit is comfort. You will not enjoy paddling a boat that doesn't fit and is uncomfortable. River running boats River running is simply exploring a river.