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A boat is a watercraft designed to float or plane on, and provide transport over water. Usually this water will be inland (lakes) or in protected coastal areas. However, boats such as the whaleboat were historically designed to be operated from a ship in an offshore environment. In naval terms, a boat is something small enough to be carried aboard another vessel (a ship). Some boats too large for the naval definition include the Great Lakes freighter, riverboat, narrowboat and ferryboat. Modern submarines can also be called boats, despite their underwater capabilities and size. This may be because the first submarines could be carried by a ship and were not capable of making independent offshore passages. Boats may be used by the military or other government interests, or for research or commercial purposes; but regardless of size, a vessel in private, non-commercial usage is almost certainly a boat.

A boat in an Egyptian tomb painting from about 1450 BCE

The roughly horizontal, but cambered structures spanning the hull of the boat are referred to as the "deck". In a ship there are often several, but a boat is unlikely to have more than one. 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 underside of a deck is the deck head. The keel is a lengthwise structural member to which the frames are fixed (sometimes referred to as a backbone). The vertical surfaces dividing the internal space are bulkheads. The front of a boat is called the bow or prow. The rear of the boat is called the stern. The right side is starboard and the left side is port. Boats of earlier eras often featured a Figurehead protruding from the front of the bows.

Types of boats

A passenger boat to the islands off the coast of the Sai Kung Peninsula of Hong Kong.

A sailboat (racing dinghy) and barge share the Mississippi River, USA.

Unusual boats have been used for sports purposes - for example, in "big bathtub races" which use boats made from bathtubs. Pumpkins have been used as boats as in the annual Pumpkin Boat Race on Lake Otsego in New York state, USA. In this race, very large, hollowed out pumpkin shells are used for boats, powered by canoe paddles.

Boat building materials

A ship's lifeboat, built of steel, rusting away in the wetlands of Folly Island, South Carolina, United States.

Until the mid 19th century most boats were of all natural materials; primarily wood. 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. They called it 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 (troweled) 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 aluminum gained popularity. Though much more expensive than steel, there are now aluminum alloys available that will not corrode in salt water, and an aluminum boat built to similar load carrying standards could be built lighter than steel. Nonetheless, boats are generally built in such a manner as to keep water from invading the hull, which would cause the boats to sink.

Platt Monfort invented Wire Plank(r)(1969), Fer-a-Lite(r)(1972), Str-r-etch Mesh(r)(1975), and Geodesic Airolite Boats(r)(1981). Fer-A-Lite(r) is a mixture of polyester resin, fiberglass, and a filler. This, along with Str-r-etch Mesh(r), could be used to build a boat in the same fashion as a ferro-cement boat, but the resulting hull would be much lighter and more resilient. Wire Plank(r) was first used in ferro-cement construction, but could also be used with Fer-a-Lite to create a medium to heavy weight hull. Geodesic Airolite Boats(r) are built using very lightweight wooden frames (geodesic) that are covered over with some lightweight heatshrinkable plastic or a synthetic fabric such as dacron coated with sealant. This tensioned skin adds to the overall strength of the structure and boats built thus are of the ultra-light variety.

Around the mid 1960s, boats made out of glass-reinforced plastic, more commonly known as fiberglass, became popular, especially for recreational boats. The coast guard refers to such boats as 'FRP' (for Fiberglass Reinforced Plastic) boats. Fiberglass boats are extremely strong, and do not rust, corrode, or rot. They are, however susceptible to structural degradation from sunlight and extremes in temperature over their lifespan. Fiberglass 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 mold, 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 fiber, kevlar(tm) 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 [1], less structurally sound materials.

Cold molding 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 fiberglass. In cold molding very thin strips of wood are laid over a form or mold 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 commonly available materials such as styrofoam or plastic, but most homebuilts today are built of plywood and either painted or covered in a layer of fiberglass and resin.

Boat propulsion

The most common means are:

Human power (rowing, paddling, setting pole etc.)
Wind power (sailing)
Motor powered screws
- Inboard
  - Internal Combustion (gasoline, diesel)
  - Steam (Coal, fuel oil)
  - Nuclear (for large boats)
- Inboard/Outboard
  - Gasoline
  - Diesel
- Outboard
  - Gasoline
  - Electric
- Paddle Wheel
- Water Jet (Jet ski, Personal water craft, Jetboat)
- Air Fans (Hovercraft, Air boat)

Severn class lifeboat in Poole Harbour, Dorset, England. This is the largest class of UK lifeboat at 17 metres long

How boats float

A boat stays afloat because its weight is equal to that of the water it displaces. The material of the boat itself may be heavier than water (per volume), but it forms only the outer layer. Inside it is air, which is negligible in weight. But it does add to the volume. The central term here is density, which is mass ('weight') per volume. The mass of the boat (plus contents) as a whole has to be divided by the volume below the waterline. If the boat floats, then that is equal to the density of water (1 kg/l). To the water it is as if there is water there because the average density is the same. If weight is added to the boat, the volume below the waterline will have to increase too, to keep the mass/weight balance equal, so the boat sinks a little to compensate.

External links

Sailboats database: sailboat data sheets all over the world
World of Boats Boat museum in Scotland
Hull Identification Numbers Explanation of International HIN formats
University of Washington Libraries Digital Collections -- Freshwater and Marine Image Bank -- Vessels Images of boats and vessels.

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