Boat

A boat is a craft or vessel designed to float on, and provide transport over, water.

A boat's propulsion can be by propellers, oars, paddles, setting poles, sails, paddlewheels, or water jets. Boats are generally smaller than ships.

Parts of a boat

See also: Glossary of nautical terms and Naval architecture

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 what keeps the boat stable. The jib is the front sail of a sailboat.

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. Many boats have a section called the gralper, designed to reduce water flow to the non-hydrodynamic parts of the boat.

Types of boats

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

See also: Boat building

Until the mid 19th century all boats were of natural materials, primarily wood. As the forests of Britain and Europe continued to be over-harvested to supply the keels of larger wooden boats and the Industrial Revolution cheapened the cost of steel, the age of the steel ship began. In the mid 20th century aluminium gained popularity, being lighter and easier to work with than steel. 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. Fiberglass provides structural strength, especially when long woven strands are laid, sometimes from bow to stern, and then soaked in epoxy (i.e., plastic) to form the hull of the boat. One of the disadvantages of fiberglass is that it is heavy and to alleviate this, various lighter components can be incorporated into the design. One of the more common methods is to use cored fiberglass, with the core being balsa wood completely encased in fiberglass. While this works, the addition of wood makes the structure of the boat susceptible to rotting. Similarly, 'advanced composites' are simply other methods designed to introduce less expensive and, by some claims, less structurally sound materials. Today, many people make their own boats or watercraft out of materials such as styrofoam or plastic.

image:http://www.tollesburysc.co.uk/Picture_gallery/Photo_competition_2005/George_Rogers_Nice%20Boat.jpg

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)
• Sails

Why boats float

See also buoyancy

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.

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