Basic Kayak Design
Designing a kayak is a complex task of balancing competing constraints, but appreciating the differences between different types of kayaks is easier when keeping design characteristics in mind. These parameters are hull cross-section, beam (largest width), length, chines, rocker, rudders, and skegs.
The cross-section of a kayak determines how stable it is on the water. Stability is often discussed in terms of Primary and Secondary stability. Primary stability is the ability of the kayak to remain tangent to the surface of the water. Secondary stability is the ability of the kayak to remain stable when the kayak is tilted.
A kayak with great primary stability has a large area of the bottom that is flat. This requires great force to tilt the kayak and will remain tangent to the surface of the water. This may appear a highly desirable feature, but waves will be more irritating since greater effort will be required to keep your body vertical.
A kayak with great secondary stability will more easily rotate around the axis of forward travel. A kayak with a circular cross section has no primary stability since there would be no tendency to remain tangent to the surface of the water. It would however be uniformly stable at all angles of tilt.
Kayak designers blend the qualities of primary and secondary stability in each design to create a specific type of kayak.
I remember my Basic 1 class when I was put in a kayak and paddled away from the dock. I immediately felt unstable and thought, "I am going to be in the water any second." I was in a kayak that has both primary and secondary stability making it a good choice for both calm and rough water. When my back was exactly vertical, the kayak would easily tilt from side to side with the tiniest nudge. To an outside observer, this change in tilt was not visible and I became used to the feel of the kayak in a few minutes. As I went through the class and learned about leaning the kayak, I noticed the secondary stability of the kayak and found that I could paddle the kayak tilted without any problem.
The kayak I used in my Basic 1 class is a touring kayak suited for touring in the Chesapeake Bay. Touring kayaks are typically longer than recreational kayaks to both make them more stable in waves and reduce the drag. Generally, for kayaks with the same beam (width) a longer kayak has less drag. In this case, the length of the kayak has to be measured at the waterline.
The final feature of the cross section of the kayak is the chines. The chines are the point where the sides of the kayak meet the bottom. A hard chine is when the sides and bottom meet and form an edge while a soft chine is a smooth curve between the sides and bottom of the hull. A hard chine will act as a directional stabilizer and feel more crisp when maneuvering.
Touring kayaks usually have an upturned bow (front) to assist with going through waves. Rocker on the other hand is a general curve of the hull from the bow to the stern (back). Kayaks with more rocker are more maneuverable. As rocker increases, the length at the waterline decreases leading to an increase in drag on the hull.
The red and white Perception Eclipse shown is made from Perception's Airlite material that is similar to the material used to make rigid one-liter water bottles. The yellow Perception Shadow is rotomolded using polyethylene. The Eclipse is stiffer than the Shadow and weighs less even though it is longer. By using Airlite, the kayak's weight is reduced and stiffness is increased. This leads to a more crisp feeling when maneuvering. Both kayaks are durable and I have not had any trouble during storage, transport, or usage.