River kayaks are designed primarily for downriver paddling.
In general, river runners are designed for down-river speed, catching eddies, and the occasional surf on a green wave (while creek boats are designed to run tight, steep, and technical whitewater).
There are a few design characteristics set river boats apart:
Weight, rocker, edge profile and volume distribution.
The same principles do apply on WhiteWater River Canoes.
We’ll start with the most obvious. Weight is not your friend. Neither kayaking, loading it onto your car, during portage or in a rescue and retrieval situation.
The term rocker refers to the curvature or angle of a boat’s hull toward the bow and stern. Boats with longer effective waterline / lower rocker are faster but do not turn as easily as boats with shorter effective waterline. Boats with longer effective waterlines typically are better suited to river-running, where speed is key to moving through large waves and holes and the boat needs to avoid being easily knocked off line.
Shorter waterlines / higher rocker tend to be slower but turn more easily. These boats are better suited to more technical whitewater where maneuverability is more important than speed.
The shape of the rocker largely determines how a boat will behave when entering the water from a vertical drop (i.e. a waterfall). Boats with rocker that remain constant as you move toward the bow or stern (called linear rocker) have a smaller possible range of boat angles that still allow the bow to stay on the surface when landing a vertical drop.
These linear rocker are common on river-runners.
Hard edges provide a “keel line” (a linear feature that resists spinning in the water) when the boat is put on edge, which allows the boat to maintain momentum moving in a relatively straight or broadly curved, trajectory. This makes boats with hard edges excellent at “carving” in and out of eddies when moving down river. Hard edges also allow for more dynamic surfing, providing good directional boat control on a wave. As a result, hard edges are more common on river running boats. The drawback of hard edges is that they provide a place for water to pile up, or “catch,” on the boat, and they can hang up more on rocks. This makes boats with hard edges more challenging to paddle in boily and dynamic water, as well as shallow rivers that involve maneuvering over, around, and on lots of rocks.
When volume is centered on the cockpit of a boat, the ends tend to be thinner in profile. Such boats feel “sportier” because the bow and stern engages the water more. This also allows the paddler to make dynamic moves like squirts more easily, and usually results in more maneuverability while surfing (because of less weight and volume in the ends). For these reasons, river running boats tend to have proportionally more of their volume around the cockpit than in the bow and stern.