A kayak is a small human-powered boat that traditionally has a covered deck, and one or more cockpits, each seating one paddler who strokes a double-bladed paddle. The cockpit is generally covered by a spraydeck that keeps the inside of the boat and the paddler's lower body dry. The spraydeck or similar waterproof covering attaches securely to the edges of the cockpit, preventing the entry of water from waves or spray, and making it possible, in some boats, to roll the kayak, capsizing and righting the boat without it filling with water or ejecting the passenger.
Kayak hulls are categorized according to the shape from bow to stern; common shapes include (1) symmetrical—the widest part of the boat is halfway between bow and stern; (2) fish—the widest part is forward of the midpoint and (3) Swedish—the widest part is aft of the midpoint.
An inflatable kayak, also known as a ducky, can usually be transported by hand using a carry bag. An outer skin, cover or shell of a conventional inflatable kayak may be made from hypalon (a kind of neoprene), a polyvinyl chloride fabric, or a polyurethane coated cloth. They can be inflated with foot, hand, or electric pumps. Multiple air compartments increase safety.
Until recently, inflatable kayaks were non-rigid, essentially pointed rafts, and best suited for use on rivers and calm water. However, some manufacturers have provided inflatable bladders captured inside non-stretch material, such as the coated cloth. Vessel rigidity increased, to a point. While portability is still adequate with these kayaks, the craft still have limitations. For example, tracking and hull shape may be less than ideal. Some hybrid kayaks with inflatable bladders and frames have been attempted. However, an adequate balance between weight, stability, speed, structural strength, and portability is somewhat elusive.