Surfboard leash

A surfboard is an elongated platform used in the sport of surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean surface wave breaking wave. They were invented in ancient Hawaii, where they were known as papa he'e nalu in the Hawaiian language, they were usually made of wood from local trees, such as koa, and were often over 15 feet (5 m) in length and extremely heavy. Major advances over the years include the addition of one or more fins on the bottom rear of the board to improve directional stability, and numerous improvements in materials and shape.

Modern surfboards are made of polyurethane or polystyrene foam covered with layers of fiberglass cloth, and polyester or epoxy resin. The result is a light and strong surfboard that is buoyant and maneuverable. Recent developments in surfboard technology have included the use of carbon fiber and kevlar composites, as well as experimentation in biodegradable and ecologically friendly resins made from organic sources. Each year, approximately 400,000 surfboards are manufactured.

The surface of the board that rests on the water, usually concave but sometimes convex. The bottom can also feature channels and other planing features shaped into the board in order to maximize or direct water flow across the board's bottom surface.

Modern surfboards often contain multiple contours on the bottom of the board, termed concaves. These concaves have different uses and vary among different types of surfboards. Most concaves on the modern shortboard begin about twelve inches (300 mm) back from the nose of the board on the bottom and then carry out through the middle to the tail of the surfboard. The purpose of concave is to direct water through the fins of the surfboard. Surfboard shapers sometimes experiment with concaves to create different drive and response characteristics on each individual surfboard.

Some older and more traditional surfboards along with many modern boards that take inspiration from these older boards utilize a convex rather than concave design on the bottom of the surfboard. These boards displace more water and sit lower in the wave than a surfboard with a concave bottom.

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Wikipedia