There are quite a few terms used to describe the various hull shapes and other design characteristics that determine a kayak's performance and "personality". This list serves as a glossary and as a primer to help you understand these terms when you encounter them. You can use this list to judge a kayak's handling before you paddle it. These "tools" will also be handy in selecting a kayak that is right for you and your needs.
 California Hull - Soft Chine |
 California Hull - Hard Chine |
A California Hull is a hull shape that combines the elements of the flat hull and a round hull. (Largely attributed to Tim Nemier of Ocean Kayak fame.) This combination provides performance in tracking, speed (rounded center keel line), greater stability (flat hull) and performance in surfing waves (hydroplaning). California hulls can be found with soft chines (like a Scupper Classic) or hard chines (like a Scrambler).
 Soft Chine |
 Hard Chine |
Chine
defines the shape of the kayak's side. Hard Chine indicates
an angle between the side of the kayak and the bottom, possibly as much
as a right angle, almost boxy. A hard chine boat tends to have greater
primary stability and lesser secondary stability. This "edge"
can also add performance in surfing, allowing the kayak to grip a wave
face and carve a turn. Soft Chine indicates a smooth curved
transition from side to bottom, giving the kayak a more cylindrical shape
thus increasing speed. Soft chine kayaks tend to have greater secondary
stability and lesser primary stability. Multi-Chine kayaks
are somewhere in-between the two.
Fishform Hull
Fishform is a term to describe an asymmetrical hull shape that has stern with less volume (narrow) than the bow with greater volume (wide). This will allow the bow to ride over the swell and waves, improving surf zone performance.
 Flare |
 Straight |
 Tumblehome |
Flare Side kayaks have sides that are shaped upward and outward. This decreases the tendency for waves to wash over the decks and increases secondary stability. Kayaks with flare sides are not as easy to Eskimo roll. The opposite of Flare is Tumblehome. Kayaks with nether flare or tumblehome are called "straight side" and perform in-between the two.
Flat Hull
Flat Hull kayaks have greater primary stability, but less secondary stability. This will provide a stable ride, but when the kayak is leaned to maximum it is more likely to tip. A flat hull kayak will also turn more readily, but not track as well on a straight path. Flat hulls increase hydroplaning. (The kayak lifts out the water and skims the surface when it reaches "planing speed".) This is a common hull shape for wave skis and surf kayaks (much like a water ski or surf board) and is often used in combination with skegs/fins for directional control.
A Keel Strip is a ridge running the length of the hull, or most of it, providing directional stability, keeping the kayak on a straight path. Sometimes this is found as a long indention, or a reverse keel.
Primary Stability is the initial feeling of steadiness. On calm waters a kayak with good primary stability will feel solid and comfortable to beginners. A flatter hull with hard chine often has good primary stability. This provides a steady platform suitable for fishing, wild life viewing & photography. In rough conditions, and extremes of lean, primary stability can fail, allowing the kayak to capsize when tipped to the maximum.
Rocker
Mild Rocker
Straight Hull
Rocker is the measure of the curvature of a kayaks hull from bow to stern. A kayak with a lot of rocker will rock from front to back, like a rocking chair. This allows for greater manuverability (turning) because the bow and stern have less resistance against the water. However this prevents the kayak from tracking well (going in a straight line). A kayak with no rocker (straight hull) will track very well, as the bow and stern have much resistance in the water. This of course will prevent easy turning. Kayaks with mild rocker are somewhere in-between.
Round Hull
Round Hull kayaks, from side to side, torpedo shaped, have increased speed with less resistance to the water when moving forward. This decreases primary stability and can increase secondary stability. This is a common hull shape for surf ski racing kayaks.
Secondary Stability is the feeling of security when the kayak is leaned to the maximum. A kayak hull with soft chines, flare sides and round hull often creates good secondary stability. Secondary stability typically is only felt when the kayak is leaned, so a kayak with good secondary stability and poor primary stability will still feel tippy to a beginner, even on flat water. Secondary stability is ideal for rough conditions, extremes of lean and for Eskimo rolling.
Sponsons
Sponsons act much like the flare sides by increasing stability when the kayak is tipped. Typically the sponsons are above the waterline and dip into the water then the kayak is leaned. This increases the width of the kayak when tipped, adding stability. When the kayak is on an even keel the sponsons are out of the water, decreasing the width and thus improving speed and glide. They can also deflect spray from the decks. (This feature on sit on tops is largely attributed to Paul Cronin of Heritage Kayak fame.)
Symmetrical Hull
Symmetrical Hulls have the same taper of shape front and back. The center of the kayak is the widest point and the width gets narrower toward the stern and bow equally with a bow and stern of the same shape. This will increase the kayak's maneuverability. An Asymmetrical hull has a bow and stern of different shapes, called Swedeform or Fishform.
Swedeform Hull
Swedeform is a tem to describe an asymmetrical hull shape that has stern with greater volume (wide) than the bow with less volume (narrow). Sometimes this is coupled with a longer bow section, and a cockpit placed further aft. This will increase speed and tracking while decreasing manuverability. A narrow bow will cut or spear through the swell and waves.
Straight
Straight Side kayaks have neither Tumblehome or Flare. No extra stability, water sheding or improved Eskimo rolling is provided.
Tumblehome
Kayaks with Tumblehome have sides that are curved upward and inboard. This increases the tendency for waves to wash over the decks. Kayaks with tumblehome are easier to Eskimo roll. The opposite of Tumblehome is Flare. Kayaks with nether flare or tumblehome are called "straight side" and perform in-between the two.
V-Hull Kayak
V-Hull kayaks have a shallow v shape when looked at from front to back. The v shape provides better tracking (straight line paddling) acting much like a keel, but decreases primary stability.
Volume refers to the internal capacity of the kayak and is sometimes expressed in gallons. It is a way of measuring the displacement or buoyancy of a kayak and can be linked to the kayak's carrying capacity.
© 2002-9 Tom Holtey
Related Articles:
Understanding Kayak Performance Based On Design Features by Scupper Pro Frank
How To Choose A Sit-on-top Kayak
Demo
Daze - How to get the most out of an outfitter's or club's kayak
demo event.
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