Kayak 

Design
Traditional kayaks typically accommodate one, two or occasionally three paddlers who sit facing forward in one or more cockpits below the deck of the boat. If used, the spraydeck or similar waterproof garment attaches securely to the edges of the cockpit, preventing the entry of water from waves or spray, and making it possible, in some styles of boat, to roll the kayak upright again without it filling with water or ejecting the paddler.
Inuit/ Eskimo Kayaks were only discovered by Europeans in the early 20th Century. Kayaks are a type of a generic class of boat of Canoe Shape. European Canoeing clubs and associations of the 19th Century used similar craft to what are now called Kayaks, but referred to these as types of Canoe. This explains the naming of the International and National Governing bodies of the sport of Canoeing

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. The oldest still existing kayaks are exhibited in the North America department of the State Museum of Ethnology in Munich.

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 is a large open sea canoe, ranging from 17 feet (5.2 m) to 30 feet (9.1 m), made with seal skins and wood. It was originally paddled with single bladed paddles and typically had more than one paddler.

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 maneuverability. A special skin jacket, Tuilik, was then laced to the kayak, creating a waterproof seal. This made the eskimo roll the preferred method of regaining posture after turning upside down (from the kayaking point of view, it\\'s not a capsize until you come out of the boat), especially as few Eskimos could swim; their waters are too cold for a swimmer to survive for very long.
The modern version of a tuilik is a spraydeck made of waterproof synthetic stretchy enough to fit tightly around the cockpit rim and body of the kayaker, which can however be released rapidly from the cockpit to permit easy exit from the boat.

Modern kayaks
Modern kayaks have evolved into numerous specialized types, that may be broadly categorized according to their application as sea kayaks, whitewater (or river) kayaks, surf kayaks, and racing kayaks (flat water, white water, or slalom), though many hybrid types exist as well, broadly labeled recreational kayaks. The label "kayak" is often misapplied to other small, human-powered vessels not descended from the kayak tradition, including multi-hull or outrigger boats and those propelled by pedals.

Sea kayaks are typically designed for travel by one or two paddlers on open water and in many cases trade maneuverability for seaworthiness, stability, and cargo capacity. Sea-kayak sub-types include open-deck "sit-on-top" kayaks,recreational kayaks, and collapsible "skin-on-frame" boats.

Whitewater kayaks are in some cases highly maneuverable boats, usually for a single paddler, and include such specialized boats as playboats and slalom kayaks. White water racers combine a fast, unstable lower hull portion with a flared upper hull portion to combine flat water racing speed with extra stability in big water: they are not fitted with rudders and have similar manoeuvrability to flat water racers.

Surf skis, are specialized narrow and long boats for racing, surfing breaking waves and surf-zone rescues. Racing kayaks are designed for speed, and usually require substantial skill to achieve stability, due to extremely narrow hulls, though downriver racing kayaks are a hybrid style with whitewater boats.

Surf Kayaks are in many respects similar to whitewater boats, however often equiped with up to three fins. Specialty surf boats typically have flat bottoms, and hard edges, similar to surf boards. The design of a surf kayak promotes the use of an ocean surf wave (moving wave) as opposed to a river or feature wave (moving water). They are typically made from rotomoldedplastic, or fiberglass.

Modern kayaks are typically constructed from rotomolded plastic, wood, fabrics over wooden or aluminum frames, fiberglass, Kevlar, or carbon fiber. Most kayaks accommodate one or two paddlers, but some special-purpose boats may accommodate more.
Sea kayaks
The sea kayak, though descended directly from traditional designs and types, is implemented in a wide variety of materials, and with many distinct design choices. Sea kayaks as a class are distinct from whitewater kayaks and other boats by typically having a longer waterline (emphasizing straight travel through the water over extreme maneuverability), and provisions for below-deck storage of cargo. Sea kayaks may also have rudders or skegs (also for enhanced straight-line tracking), and such features as upturned bow or stern profiles for wave shedding. Modern sea kayaks often have two or more internal bulkheads to provide watertight internal sections for flotation and waterproof storage. Sea kayaks, unlike most whitewater kayaks, may be built to accommodate two or sometimes three paddlers. Certain sea kayaks can even be used for surfing.

Sit-on-tops
Sealed-hull (unsinkable) craft were developed in the past for leisure use, as derivatives from surfboards (e.g. paddle or wave skis), or for surf conditions. Variants include planing surf craft, touring kayaks, and sea marathon kayaks. Increasingly, manufacturers are building leisure \'sit-on-top\' variants of extreme sports craft these are normally built using polyethylene to ensure strength and keep the price down, often with a skeg (fixed rudder) for directional stability. Water that enters the cockpit drains out through scupper holes - tubes that run from the cockpit to the bottom of the hull. Sit-on-top kayaks usually come in single and double (two paddler) designs, although a few models accommodate three or four paddlers. Sit-on-top kayaks are particularly popular for fishing and SCUBA diving, since participants need to easily enter and exit the water, change seating positions, and access hatches and storage wells. Ordinarily the seat of a sit-on-top is slightly above water level, so the center of gravity for the paddler is higher than in a traditional kayak. To compensate for the center of gravity, a sit-on-top is often wider than a traditional kayak of the same length, and is considered slower as a result.
 
Recreational kayaks
Recreational kayaks are designed for the casual paddler interested in fishing, photography, or a peaceful paddle on a lake or flatwater stream; they presently make up the largest segment of kayak sales. Compared to other kayaks, recreational kayaks have a larger cockpit for easier entry and exit and a wider beam (27–30 inches) for more stability on the water; they are generally less than twelve feet in length and have limited cargo capacity. Using less expensive materials like polyethylene and including fewer options keep these boats inexpensive (US$300–$580). Most canoe/kayak clubs offer introductory instruction in recreational boats as a way to enter into the sport. Sometimes advanced paddlers still use recreational kayaks. They can fit all levels, but sometimes do not perform as well in the sea. The recreational kayak is usually a type of touring kayak.
 
Whitewater kayaks
Plastic whitewater kayaks are rotomoulded in a semi-rigid, high impact plastic, which is usually polyethylene. Careful construction is needed to ensure that the completed boat will remain structurally sound when subjected to the incredible forces of fast-moving water. A plastic hull allows these kayaks to bounce off rocks without suffering leaks, although they can be scratched and eventually worn through with enough use. Standard whitewater boats are shorter than other types of kayaks, ranging from 4 to 10 feet (1.25 to 3 metres) long. There are two main types of whitewater kayak, and most experienced paddlers own one of each.

One type, known as the playboat, is short, with a scooped bow and blunt stern. These are slow and not extremely stable, but they are incredibly maneuverable. Their primary use is performing tricks in single water features or short stretches of river. In playboating or "freestyle" competition (also known in some parts of the US as "rodeo" boating), kayakers exploit the complex currents of rapids to do a series of tricks, which are scored for skill and style.

The other primary type is the creekboat, which gets its name from its purpose: running narrow, low-volume waterways. Creekboats are longer and have far more volume than playboats, which makes them faster and higher-floating. They are also designed to be very stable. Many paddlers use creekboats in "short boat" downriver races, and they are often seen on large rivers where their extra stability and speed may be necessary to get through the rapids.
 
 Fishing kayaks
While native people of the Arctic regions did not rely on kayaks for fishing, in recent years sport fishing from kayaks has become popular in both fresh and salt water, especially in warmer regions. Specially designed fishing kayaks have emerged, with designs similar to those of recreational sit-in and sit-on-top kayaks characterized by very wide beams (up to 36 inches) that increase lateral stability. Some fishing kayaks are equipped with outriggers for this reason, and the newer twinhull models are stable enough to enable paddling and fishing in the standing position. In the past several years kayak fishing has become a huge sport. The popularity has grown due to the ease of entry. Kayaks can be purchased inexpensively and have little maintenance costs. Kayaks can be stored in small spaces and launched quickly. Many kayak dealers across the U.S. have started customizing their kayaks for fishing.
 
Design of traditional style kayaks
The design of different types of kayak is largely a matter of trade-offs between directional stability ("tracking") and maneuverability, and between stability (both Primary stability and secondary stability) and overall speed.

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 (5.8 m). A flat water racing K1\'s maximum length governed by the ICF is 17 feet (5.2 m). Whitewater kayaks, which generally depend upon river current for their forward motion, are built quite short, to maximize maneuverability. These kayaks rarely exceed eight feet in length, and some specialized boats such as playboats may be only six feet long. The design of recreational kayaks is an attempt to compromise between tracking and maneuverability, while keeping costs reasonable; their length generally ranges from nine to fourteen feet.

Rocker: Length alone does not fully predict the maneuverability 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 (5.5 m) 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 (4.9 m). 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 maneuverability 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 (in back) of the midpoint.

The presence or absence of a V bottom at various points affects the kayak\'s tracking and maneuverability. 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.

Beam profile: 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 with less buoyancy away from the centerline. 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.

Until recently, whitewater kayaks had very rounded and rockered hulls, but changes in design philosophy have led to whitewater kayaks with very flat planing hulls that allow them to surf on top of moving water rather than float in the water (displacement hull).