Design Principles of Kayaks
The displacement of a kayak can refer to one of two things: its overall water displacement or, in the case of whitewater kayaks, the shape of its hull.
The Design Water Line (DWL) determines the total amount of weight the kayak was designed to carry. The combined weight of the boat, kayaker, and gear should not exceed the DWL.
In whitewater kayaks, a displacement hull has a rounded profile that dips beneath the water and “displaces” water. This compares to a planing hull which has a flat surface from edge to edge, allowing them to “plane” over the surface of the water.
The longer the length of the kayak’s hull, the faster it will travel through the water. It will also track, or follow a straight line, better than a shorter length. The trade off for this is reduced maneuverability and stability, particularly in kayaks with a narrow beam profile. Sea kayaks and touring kayaks often have longer hulls and narrower profiles to allow them to track straight, achieve higher speeds, and carve through smaller waves.
The rocker is a measurement of how much a kayak rises at the bow and stern. The higher the rocker is, the more maneuverable but slower the kayak is. The rocker is an important measurement for kayaks that need to stay agile in the water, such as whitewater kayaks and creekboats.
The beam profile of a kayak is measured by the overall width of a kayak’s cross section. The wider the beam profile, the more stable the kayak is and the more displacement can be packed into a shorter hull. As a rule, recreational kayaks have a wider beam profile and are more stable, while touring and sea kayaks have a narrower beam profile and are therefore less stable.
A kayak’s stability is a measurement of how much the boat tips, or rocks back and forth, when displaced from level by paddler weight shifts. Stability is often split into two separate measurements, initial and secondary.
- The initial stability of a kayak is how stable or unstable the kayak first feels when you get into it.
- The secondary stability is how stable the kayak feels when it is rolled onto its edge, as you would do when turning sharply.
Hull Surface Profile
The hull surface profile of a kayak is normally an indication of where the widest part of the boat lies in comparison to the seating position of the paddler.
- Symmetrical: The widest part of the boat is halfway between bow and stern.
- Fish Form: The widest part is forward (in front) of the midpoint.
- Swede Form: The widest part is aft (behind) the midpoint.
The seating position of a kayak depends on its use, and can vary significantly between types of kayaks. Most modern kayaks have placed the paddler in a position called the “L” kayaking position. This requires that the paddler be seated with their legs stretched in front of them, in a right angle.
Steering a kayak requires the kayaker to be able to use their lower body, leaning and twisting at the waist to maneuver their boat. This means putting pressure on the sections of the boat which are in contact with the paddler’s body. To make sure this does not result in injury or discomfort, modern kayaks often have adjustable internal foot, knee, and thigh braces, or padding at potential contact points.