Components of kayak hull design: Assumed general knowledge kayak of nomenclature.
Length- Refers to the overall length of the kayak from bow to stern, which may be different than the length of the waterline. The longer the water line a kayak has the more efficient it will be. A long water line also helps a kayak to track (paddle in a straight line) better.
Width- Refers to the measured distance of the kayak at its widest point. Wider kayaks are more stable but tend to be less efficient. A narrow kayak will be less stable but be more efficient through the water. (Stability in this case refers to initial stability, how stable a boat is sitting flat on the water)
Depth- Is the measured distance from the lowest point in the hull up to the deck. Deeper kayaks will accommodate larger paddlers and make it easier to fit more gear. A deeper boat will also have more sail area or area above the surface of the water causing it to be more heavily influenced by wind and waves than a boat with a lower profile or decreased depth would be. A shallower kayak is built with Medium and Small stature paddlers in mind. You may also choose to paddle a low volume boat if you are tackling more dynamic paddling environments like those found in the coastal zone. The lower volume
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 maneuverability (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.
Chine- There are several types of chine when is comes to designing a kayak. Chine refers to the shape of the side of the kayak as how it applies to secondary stability or when the boat is on edge. There are three types: Soft, Hard and multichine. Lean a hard-chine kayak over far enough, and the chine will start to function as a keel. However, since the chine is curved, the boat starts to carve a turn. You get some benefit from leaning a multi-chine kayak while turning. In a hard-chine boat this effect is more pronounced and felt at a lower angle of heel (in other words, even when leaning less) than in a multi-chine boat. 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.
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.
Rudder- A device placed on the stern f the kayak to aid in maneuverability and tracking especially when paddling in wind and waves.
Advantages- Make controlling a kayak (Especially over 18ft) much easier. Can be used in concert with edging to enhance maneuverability.
Disadvantages- Can be relied on to heavily and hinder development of skill. Creates more surface above the water when considering windage and breaking waves. Has “squish in the foot pedals”
Skeg- Is a small fin that protrudes from the stern of the kayak under water that can be partially raised or lowered depending on conditions.
Advantages- Aids the boat in tracking, set it and forget it. Clears the back deck. Decreases “squish in foot pedals”
Disadvantages- Less maneuverable than the rudder. Skeg box or house can fill with debris and foul the mechanism. The skeg box takes up a fair bit of room in the rear hatch.
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.
Swedeform- is a term 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 maneuverability. A narrow bow will cut or spear through the swell and waves.
Examples
Inland Expedition- Long and narrow with a low amount of rocker. The depth of the boat can be moderate to high to increase capacity. Soft chine for increased speed.
Coastal Expedition- Not quite as long and narrow as its inland cousin this boat will also have more rocker to combat rougher sea states and make it more nimble. The volume will decrease slightly to take away excess surface area above the water line. Usually soft chine for added speed.
Coastal Play (surf)- This boat will be shorter than the expediditon class boats. There will be and very high amount of rocker and a very low depth to the boat. The more performance oriented in the class will have hard chine while others may have multi or soft chine.