Kayak
From Wikipaddle
A kayak is a small human-powered boat. It typically has a covered deck or cockpit covered by a spraydeck. It is propelled by a double-bladed paddle by a sitting paddler. The kayak was used by the native Ainu, Aleut and Eskimo hunters in sub-Arctic regions of Northeast Asia, North America and Greenland. Modern kayaks come in a wide variety of designs and materials for specialized purposes.
Kayaks typically accommodate one or two paddlers (and occasionally more) who sit facing forward in one or more cockpits below the deck of the boat. The spraydeck attaches securely to the edges of the cockpit, preventing the entry of water from waves or spray, and making it possible, in most styles of boat, to role the kayak upright again without it filling with water or ejecting the paddler(s).
Kayaks differ distinctly in design and history from canoes, which are more flat-bottomed boats propelled by single-bladed paddles by a kneeling paddler, although some modern canoes may be difficult for a non-expert to distinguish from a Kayak. Kayaks are often called canoes in Great Britain and Ireland.
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Origins
Kayaks were originally developed by indigenous people living in the Arctic regions, who used the boats to hunt on inland lakes, rivers and the coastal waters of the Arctic Ocean, North Atlantic, Bering Sea and North Pacific oceans. These first kayaks were constructed from stitched animal skins such as seal stretched over a wooden frame made from collected driftwood, as many of the areas of their construction were treeless. Archaeologists have found evidence indicating that kayaks are at least 4000 years old.
Though the term "kayak" is now used broadly for this class of boat, native people made many different types of boat for different purposes. The baidarka developed by indigenous cultures in Alaska was also made in double or triple cockpit designs, and was used for hunting and transporting passengers or goods. An umiak ("women's boat") is a larger open decked boat ranging from 17 feet to 60 feet, made with seal skins and wood. It was paddled with single bladed paddles and typically had more than one paddler. It is thought the kayak originally started out as a decked over umiak and evolved into its traditional form.
The word "kayak" means "man's boat" or "hunter's boat", and native kayaks were a very personal craft, built by the man who would use them (with assistance from his wife, who would sew the skins) fitting his measures, for maximum manoeuvrability. A special skin jacket, a Tuilik (the ansestor of the Spraydeck), was then laced to the kayak, creating a waterproof seal. This made the eskimo roll the preferred method of regaining posture after a capsize, especially as few Eskimos could swim.
The builder used found materials and anthropomorphic measurements, using his own body, to create a kayak conforming closely to his own body. For example - typically the length was three times the span of his outstretched arms. The width at the cockpit was the width of the builder's hips plus two fists. The typical depth was his fist plus the outstretched thumb (hitch hiker style). Thus typical dimensions were about 17 feet long by 20-22 inches wide by 7 inches deep. This measurement style confounded early European explorers who tried to duplicate the kayak because each kayak was a little different.
Contemporary kayaks trace their origins primarily to the native boats of Alaska, Northern Canada, and Southwest Greenland. Wooden kayaks and fabric kayaks on wooden frames (such as the Folding Kayak) were dominating the market up until 1950s, when fibreglass boats were first introduced. Rotomolded plastic kayaks first appeared in 1973, and most modern kayaks are now produced using this method.
Modern Kayaks
| Types of Kayaks |
|---|
| Sea Kayaks |
| Whitewater Kayaks |
| Playboats |
| Slalom Kayaks |
| Surf Kayaks |
Modern kayaks have evolved into numerous specialized types, that may be broadly categorized as Sea Kayaks, Whitewater (or River) Kayaks, Surf Kayaks, and Racing Kayaks, though many hybrid types exist as well. Sea Kayak are typically designed for travel by one or two paddlers over long distances on open seas and trade manoeuvrability for seaworthiness, stability, and cargo capacity. Whitewater Kayaks are highly manoeuvrable boats, usually for a single paddler, and are designed to be able to turn quickly and move around obsticles in the flow of the water. They include such specialized boats as playboats and Slalom Kayaks. Surf Kayaks, often called "surf skis", are specialised narrow and long boats for surfing breaking waves and surf-zone rescues. Racing kayaks are designed for speed, predominantly in a straight line, and usually require substantial skill to achieve stability due to extremely narrow hulls. Downriver racing kayaks do exist in the form of Wave-hoppers or as a hybrid style of whitewater boats.
Modern kayak design
The design of different types of kayak is largely a matter of three dimensions of trade-off:
- Directional stability ("tracking") and manoeuvrability,
- Primary and secondary stability,
- Overall speed and overall lateral stability.
The first and third trade-offs can be largely avoided in twin hull kayak designs. Though these have much poorer manoeuvrability.
Length:
As a general rule, a longer kayak is faster while a shorter kayak may be turned more quickly - but the higher potential top speed of the longer kayak is largely offset by increased friction. Kayaks that are built to cover longer distances such as touring and sea kayaks are themselves longer, generally between 16 and 19 feet. A flat water racing K1's maximum length governed by the ICF is 17 feet. Whitewater kayaks, which generally depend primarily upon river current for their forward motion, are built quite short, to maximize manoeuvrability. These kayaks rarely exceed eight feet in length, and some specialized boats such as playboats can be less than six feet long. The design of recreational kayaks is an attempt to compromise between tracking and manoeuvrability, while keeping costs reasonable; their length generally ranges from nine to fourteen feet.
Rocker:
Length alone does not fully predict the manoeuvrability of a kayak: a second design element is rocker, the curvature of the kayak from bow to stern. A heavily "rockered" boat has more lengthwise curvature than a boat with little or no rocker, meaning that the effective waterline of the rockered boat is less than for a kayak with no rocker. For example, an 18 foot kayak with no rocker will be entirely in the water from end to end. In contrast, the bow and stern of an 18 footer with rocker will be out of the water, so its lengthwise waterline may be only 16 ft. Rocker is generally most evident at the ends, and in moderation improves handling. Similarly, although a whitewater boat may only be a few feet shorter than many recreational kayaks, because the whitewater boat is heavily rockered its waterline is far shorter and its manoeuvrability far greater.
Hull form:
Kayak hull designs are divided into categories based on the shape from bow to stern and on the shape of the hull in cross-section. Bow-to-stern shapes include:
- Symmetrical: the widest part of the boat is halfway between bow and stern.
- Fish form: the widest part is forward of the midpoint.
- Swede form: the widest part is aft (back) of the midpoint.
The presence or absence of a V bottom at various points affects the kayak's tracking and manoeuvrability. A V tends to improve the kayak's ability to travel straight (track), but reduces the ease of turning. Most modern kayaks have steep Vee sections at the bow and stern, and a very shallow Vee amidships.
Hull shapes are categorized by the roundness (or flatness) of the bottom, whether the bottom comes to a "V" at various points on the hull, and by the presence, absence, and severity of a chine, where the side and bottom of a hull meet at an angle, creating another edge below the gunwales. This design choice determines the tradeoff between primary and secondary stability. The hull design determines the relative primary stability and secondary stability of a kayak, the resistance of the boat to tipping and to ultimate capsize, respectively.
Primary and secondary stability:
Although every kayak will rock from side-to-side, wider kayaks with more buoyancy away from the centerline will present more resistance to tipping and thus feel less likely to capsize than a narrow one. Flat-bottomed boats that push their volume away from the centerline will also feel more stable than rounded or V-shaped hull shapes that distribute buoyancy more evenly.
While flat-bottomed boats have more primary (sometimes called "initial") stability, and feel more stable to the beginner they usually have less secondary stability. Once they do begin to tip, they capsize quickly and suddenly. Rounder-bottomed boats are quite the opposite — having lower initial or primary stability and (usually) greater secondary stability. The chine in some boats increases secondary stability by effectively widening the beam of the boat when it is heeled (tipped).
Secondary stability refers to final stability, or additional resistance to capsizing as a kayak approaches capsizing. Rounder-bottomed boats present a greater cross-section to the water as they are tipped from level ("heeled"), while very flat-bottomed boats present less. Sea kayaks, designed for open water and rough conditions, are generally narrower (22-25 inches) and have more secondary stability than recreational kayaks, which are wider (26-30+ inches), have a flatter hull shape, and more primary stability. Kayaks with only moderate primary, but excellent secondary are, in general, considered more seaworthy, especially in challenging conditions.
Until recently, whitewater kayaks had very rounded and rockered hulls, but changes in design philosophy have lead to whitewater kayaks with very flat planing hulls that allow them to sit on top of the water rather than in the water (displacement hull).
Cockpit Design
When Kayaks were predominantly made of fibreglass, spraydecks were in their early days of development and the materials used were not elastic or waterproof enough to cover large "deck" areas. This lead to kayak designs with small cockpits, encasing the paddler tightly. These however had a major draw-back, they made it difficult to get out of the kayak, especially in a vertical pin situation.
Most modern kayaks now feature a "Key-Hole" deck design, which is large, elongated and key-hole shaped. These allow the paddler to get their legs out of the kayak in vertical pin situations, and with the wide use of neoprene spraydecks the fitting is no longer an issue.
Kayak Construction
Initial kayak design typically takes place with construction of a wooden or foam model called a plug (clay is also sometimes used for fine designs). This is cut out, reshaped and modified until it is suitable, and then finely sanded down and smoothed off. A cast or mould is made from this original, and this mould is then used to construct all further versions. Typically modern kayak designers will go through several plug designs and make prototype moulds to form fully functional kayaks for testing before final refinement and production beings.
Fibreglass
Most kayaks were from made from fibreglass up until 1973. These were light, relatively strong and easy to construct, and they could be refined into very precise designs. They were also easily repaired with a little time and a resin kit. They were made by pasting layers of fibreglass onto the inside of a thick, two-part, fibreglass mould. The fibreglass is alowed to set and the mould is split apart, leaving the shell or hull of the kayak complete.
Modern Slalom kayaks are still made from fibreglass which allows them to be very lightweight. .
Rotomoulded Plastic
Most modern kayaks tend to be plastic bases, and are formed using a rotation-moulding process. This uses plastic dust at high temperature, low pressure spun in a biaxial rotation mould (ie. a mould spun through two axis). Unlike for fibreglass kayaks, the rotomould needs to be made of something sturdy and a good conductor of heat, and typically aluminium is used. This adds high costs to the production, however it is the most efficient way of construction high quality plastic boats.
Plastic has an advantage over fibreglass in that it is impact resistant, and more ductile, meaning it won't break apart on impact. It does however mean that boats typically become very scratched on the underneath, however the plastic is normally thick enough to ensure that these are usually only superficial scratches.
- Liquid Logic have a set of Blog posts describing how they make their Plastic Whitewater kayaks. - Part 1 - Part 2
Trivia
The word "kayak" is a palindrome — a word spelled the same forward and backward.
External links
- USA Canoe and Kayak The National Governing Body of Kayaking in the USA
- The Kayaking Journal
- Qajaq USA, A non-profit committed to promoting Greenland style kayaking
- British Canoe Union The National Governing Body of Kayaking in the UK
