Kayaks have become an increasingly popular means of enjoying sporting and leisure boating activities. Kayaks resemble canoes in that both are long, narrow, lightweight paddle boats which are pointed at both ends. Like canoes, kayaks have a hull, which is the hollow bottom shell of the boat. However, several features distinguish kayaks from canoes. Kayaks are water displacement vessels, which means they float just below the surface, forcing the water to be pushed aside as they move. Canoes, on the other hand, float on the water's surface. Because the kayak sits lower in the water, it requires a deck. The deck is the semienclosed covering on the kayak's top. The purpose of the deck is to keep waves from washing over the edges of the boat and filling the hull with water. The cockpit is the opening placed in the center of the deck where the kayaker sits. The cockpit is surrounded by a raised lip called the coaming. Other kayak features include interior braces and bulkheads, interior flotation devices, and a cord called the grab loop attached to each end for towing and mooring. Some kayaks include elastic strapping or bungee cord s across the deck for carrying lightweight equipment. Other kayaks have waterproof hatches that give access to the forward and aft compartments for additional storage. Some sea kayaks have a rudder controlled by foot pedals to assist steering.
Kayaking is an excellent way to exercise and relax at the same time. A person sits upright in a kayak with legs extended to the front into the hollow hull. A double-bladed paddle is used for propulsion. Kayakers pull their crafts through the water by paddling with left and right strokes. A kayaker wears a life vest and, sometimes, a protective helmet. Waterproof spray skirts may also be worn. Spray skirts fit around the upper torso of the kayaker and attach to the deck around the cockpit opening to prevent water from splashing into the cockpit when navigating rough water.
The two most common uses of kayaks are racing and recreational boating. Racing kayaks are built for speed and maneuvering on river rapids, while recreational kayaks are built for comfort and longer distance paddling on oceans and lakes. Other design features distinguish racing from recreational kayaks. For example, racing hulls are narrow and v-shaped, whereas recreational hulls are more rounded. The number of seating areas for racing would typically be not more than two, while up to four seats might be provided for recreational purposes. The length, width, and weight would vary as well. Racing models tend to be shorter in length, 11-13 feet (3-4 m) long, and much lighter than recreational models. Some highly specialized racing kayaks weigh less than 25 pounds (11 kg). A typical recreational model will be 13-20 feet (4-6 m) long and may weigh as much as 75 pounds (34 kg). Most designs are no wider than 35 inches (89 cm) across.
The design and manufacture of kayaks have gone through many stages over the centuries, from primitive, handmade crafts used for survival to mass-produced sporting boats. Archeological evidence shows that kayaks were used at least 2,000 years ago by Eskimos for transportation, hunting, and
By A.D. 900, kayaks were being used in Europe. New designs in frames and coverings addressed the need to easily transport the kayak over land. One of these designs was a revolutionary collapsible kayak model called a foldboat which was invented in Germany in the 1800s. The foldboat used a rubberized canvas outer layer stretched over a folding tubular frame. The foldboat could be disassembled and carried in just two suitcases.
More recently, the primary use of kayaks has shifted from hunting and transportation to recreation and competitive sport. Kayaking for recreation began on rivers and lakes in the late 1800s. Sea kayaking was widely popularized when Percy Blanfold designed and built thousands of canvas-covered plywood and lumber kayaks in the 1950s and 1960s. Kayaking as a competitive sport began during the Summer Olympic Games in Germany in 1936 and has since gained international appeal.
Modern kayaks are built from covered wooden frames or from shells of fiberglass or plastic. Wooden kayaks most closely resemble the ancient Eskimo rib and cross frame construction. They are considered the classic design, and can be built from scratch in a very short time or assembled from kits. Durable marine or exterior-grade plywood is used for the frame. Waterproof glue and mechanical fasteners join the wooden pieces. Copper tacks or stainless steel staples are used for attaching the cotton canvas or cotton duck fabric to the frame. These coverings are treated and finished with airplane dope or exterior paint to waterproof and strengthen the fabric.
In the 1950s, fiberglass-reinforced resins
Polyethylene and the use of recycled plastics revolutionized kayak construction again in the early 1980s. The raw materials and manufacturing process for this latest advancement are described next.
The idea that a kayak shell can be made from recycled plastics is very appealing to many environmentally-minded boaters. The primary ingredient of a plastic kayak is polyethylene. Polyethylene is a tough, waxy-textured material that is unaffected by water and many chemicals. It can be repeatedly softened by heating and hardened by cooling. These characteristics make it excellent for the manufacture of kayaks. Adequate supplies of polyethylene recycled from plastic beverage bottles are now available with sufficient durability and strength for use in making kayaks.
Polyethylene is also used to make the seats in a kayak. The flotation devices, bulk-heads, and padding for the kayaker's hips, knees, and heels are often made of a closedcell foam like Ethafoam. The rudder pedals or foot braces are usually made from a lightweight, corrosion-resistant metal like aluminum, as is the rudder itself. The grab loop may be nylon rope with a plastic or wooden toggle, or handle.
The body of a polyethylene kayak is a long, hollow shell of uniform thickness made by a process called rotational molding. After the shell is made, the seat and other components are added in a manual assembly process. The shell may be molded in one piece, or it may be made from two separate pieces which are joined later. Rotational molding requires fairly rounded contours, so one-piece shells cannot have sharp intersections between surfaces. If the design requires a sharper intersection—such as between the hull and the deck, for example—then a two-piece shell is used. The process for making the two-piece shell is described here.
Most of the quality control checks for a rotationally molded kayak are in the molding process. Maintaining the proper rotation speed and oven temperature are critical to producing shells with uniform thickness. Care is required during cooling to avoid warping the shell. The duration of the heating and cooling cycles, and the intervals between those stages, must also be controlled precisely.
Kayaking continues to grow as a recreational and competitive sport. Improved performance in competitive kayaking will depend on modern technology for new design and construction methods, and may result in the use of new materials. At the same time, many kayak enthusiasts will demand that these materials be environmentally benign, such as recycled plastics.
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— David N. Ford