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Boats

For other uses, see Boat (disambiguation).

A boat is a watercraft of any size designed to float or plane, to work or travel on water. For small boats, this is typically inland (lakes) or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a vessel small enough to be carried aboard another vessel (a ship). Another less restrictive definition is a vessel that can be lifted out of the water. Some definitions do not make a distinction in size, as 1000-foot bulk freighters on the Great Lakes are called oreboats.

Boats come in a wide variety of shapes, sizes and construction due to intended purpose, available materials and local traditions. Canoe type boats have a long history and various versions are used throughout the world for transportation, fishing or sport. Fishing boats vary widely in style partly to match local conditions. Pleasure boats represent a less practical approach, including ski boats, pontoon boats, sailboats. House boats may be a vacation or provide long-term housing. Small boats also provide transport or move cargo (lightering) from large ships. Lifeboats are an important safety measure.

History


Dugouts are the oldest boats archaeologists have found, dating back about eight thousand years.[2]


Boats have served as transportation since early times.[3] Circumstantial evidence, such as the early settlement of Australia over 40,000 years ago, findings in Crete dated 130,000 years ago,[4] and findings in Flores dated to 900,000 years ago,[5] suggest that boats have been used since very ancient times. The earliest boats are thought to have been logboats,[6] the oldest boats found by archaeological excavation dating from around 7,000–10,000 years ago. The oldest recovered boat in the world is the Pesse canoe, a dugout, or hollowed tree trunk from a Pinus sylvestris and constructed somewhere between 8200 and 7600 BC. This canoe is exhibited in the Drents Museum in Assen, Netherlands;[7][8] other very old dugout boats have been recovered.[9][10][11] A 7,000 year-old seagoing reed boat has been found in Kuwait.[12] Boats were used between 4000 and 3000 BC in Sumer,[3] ancient Egypt[13] and in the Indian Ocean.[3]

Boats played a very important part in the commerce between the Indus Valley Civilization and Mesopotamia.[14] Evidence of varying models of boats has also been discovered in various Indus Valley sites.[15][16] The Uru wooden big boat was made in Beypore a village in south Calicut, Kerala, in southwestern India. These have been used by the Arabs and Greeks since ancient times as trading vessels. This mammoth wooden ship was constructed using teak, without any iron or blueprints and which has transportation capacity of 400 tonnes.

The accounts of historians Herodotus, Pliny the Elder, and Strabo suggest that boats were being used for commerce and traveling.[15]

Types

Main article: List of boat types


Boats can be categorized into three types:

  • Unpowered or human-powered boats. Unpowered boats include rafts and floats meant for one-way downstream travel. Human-powered boats include canoes, kayaks, gondolas and boats propelled by poles like a punt.
  • Sailboats, which are boats propelled solely by means of sails.
  • Motorboats, which are boats propelled by mechanical means, such as engines.
    • Ski boats are specialized motorboats specifically designed to safely tow one or more water skiers. This is achieved by using a high-horsepower, marinized automobile engine, usually positioned in the midsection and driven through a direct drive to the propeller. A skier is pulled on a towrope attached to a tow bar located in front of the drive motor and affixed to the bottom of the hull. Each approved towboat must meet or exceed a preset set of standards defined by the USA Water Ski Federation, Formerly American Water Ski Association, AWSA.

Parts and terminology

Several key components make up the main structure of most boats. The hull is the main structural component of the boat which actually provides buoyancy for the boat. Also there is the gunnel which is the sides of the boat. They offer protection from the water and makes the boat harder to sink. The roughly horizontal, but chambered structures spanning the hull of the boat are referred to as the deck. In a ship there are often several decks, but a boat is unlikely to have more than one, if any at all. Above the deck are the superstructures. The underside of a deck is the deck head.

An enclosed space on a boat is referred to as a cabin. Several structures make up a cabin: the similar but usually lighter structure which spans a raised cabin is a coach-roof. The "floor" of a cabin is properly known as the sole, but is more likely to be called the floor (a floor is properly, a structural member which ties a frame to the keelson and keel). The vertical surfaces dividing the internal space are bulkheads.

The keel is a lengthwise structural member to which the frames are fixed (sometimes referred to as a backbone).

The front (or fore end) of a boat is called the bow. Boats of earlier times often featured a figurehead protruding from the front of the bows. The rear (or aft end) of the boat is called the stern. The right side (facing forward) is starboard and the left side is port.

Building materials


Until the mid-19th century most boats were of all natural materials; primarily wood although reed, bark and animal skins were also used. Early boats include the bound-reed style of boat seen in Ancient Egypt, the birch bark canoe, the animal hide-covered kayak and coracle and the dugout canoe made from a single log.

Bill Streever describes a boat made by the native Inupiat people in Barrow, Alaska as "a skin boat, an umiaq, built from the stitched hides of bearded seals and used to hunt bowhead whales in the open-water leads during spring...".[17]

By the mid-19th century, many boats had been built with iron or steel frames but still planked in wood. In 1855 ferro-cement boat construction was patented by the French as Ferciment. This is a system by which a steel or iron wire framework is built in the shape of a boat's hull and covered (trowelled) over with cement. Reinforced with bulkheads and other internal structure, it is strong but heavy, easily repaired, and, if sealed properly, will not leak or corrode. These materials and methods were copied all over the world, and have faded in and out of popularity to the present. As the forests of Britain and Europe continued to be over-harvested to supply the keels of larger wooden boats, and the Bessemer process (patented in 1855) cheapened the cost of steel, steel ships and boats began to be more common. By the 1930s boats built of all steel from frames to plating were seen replacing wooden boats in many industrial uses, even the fishing fleets. Private recreational boats in steel are uncommon. In the mid-20th century aluminium gained popularity. Though much more expensive than steel, there are now aluminium alloys available that will not corrode in salt water, and an aluminium boat built to similar load carrying standards could be built lighter than steel.

Around the mid-1960s, boats made of glass-reinforced plastic, more commonly known as fibreglass, became popular, especially for recreational boats. The United States Coast Guard refers to such boats as 'FRP' (for fibre-reinforced plastic) boats.

Fibreglass boats are strong, and do not rust (iron oxide), corrode, or rot. They are, however susceptible to structural degradation from sunlight and extremes in temperature over their lifespan. Fibreglass provides structural strength, especially when long woven strands are laid, sometimes from bow to stern, and then soaked in epoxy or polyester resin to form the hull of the boat. Whether hand laid or built in a mould, FRP boats usually have an outer coating of gelcoat which is a thin solid colored layer of polyester resin that adds no structural strength, but does create a smooth surface which can be buffed to a high shine and also acts as a protective layer against sunlight. FRP structures can be made stiffer with sandwich panels, where the FRP encloses a lightweight core such as balsa or foam. Cored FRP is most often found in decking which helps keep down weight that will be carried above the waterline. The addition of wood makes the cored structure of the boat susceptible to rotting which puts a greater emphasis on not allowing damaged sandwich structures to go unrepaired. Plastic based foam cores are less vulnerable. The phrase 'advanced composites' in FRP construction may indicate the addition of carbon fibre, Kevlar or other similar materials, but it may also indicate other methods designed to introduce less expensive and, by at least one yacht surveyor's eyewitness accounts,[18] less structurally sound materials.

Cold moulding is similar to FRP in as much as it involves the use of epoxy or polyester resins, but the structural component is wood instead of fibreglass. In cold moulding very thin strips of wood are laid over a form or mould in layers. This layer is then coated with resin and another directionally alternating layer is laid on top. In some processes the subsequent layers are stapled or otherwise mechanically fastened to the previous layers, but in other processes the layers are weighted or even vacuum bagged to hold layers together while the resin sets. Layers are built up thus to create the required thickness of hull.

People have even made their own boats or watercraft out of materials such as foam or plastic, but most homebuilts today are built of plywood and either painted or covered in a layer of fibreglass and resin.

Propulsion

The most common means of boat propulsion are:

An early uncommon means of boat propulsion was the water caterpillar. This moved a series of paddles on chains along the bottom of the boat to propel it over the water and preceded the development of tracked vehicles.[19]

Buoyancy

A floating boat displaces its weight in water. The material of the boat hull may be denser than water, but if this is the case then it forms only the outer layer. If the boat floats, the mass of the boat (plus contents) as a whole divided by the volume below the waterline is equal to the density of water (1 kg/l). If weight is added to the boat, the volume below the waterline will increase to keep the weight balance equal, and so the boat sinks a little to compensate.

See also

References

External links

  • University of Washington Libraries Digital Collections – Freshwater and Marine Image Bank, (enter search therm "vessels" for images of boats and vessels.)

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