Ballast isdense material used as aweight to provide stability to a vehicle or structure. Ballast, other thancargo, may be placed in a vehicle, often aship or thegondola of aballoon orairship, to providestability. A compartment within a boat, ship,submarine, or other floating structure that holds water is called aballast tank. Water can be moved in and out from the ballast tank to balance the ship. In a vessel that travels on the water, the ballast will be kept below the water level, to counteract the effects of weight above the water level.[1] The ballast may be redistributed in the vessel or disposed of altogether to change its effects on the movement of the vessel.
The basic concept behind the ballast tank can be seen in many forms of aquatic life, such as theblowfish or members of theargonaut group ofoctopus.[2] The concept has been invented and reinvented many times by humans to serve a variety of purposes.
In the fifteenth and sixteenth century, the ballast "did not consist entirely of leakage, but of urine, vomit, and various foul food leavings that lazy sailors discharged into the ballast contrary to orders, in the belief that the pumps would take care of it."[3] In the eighteenth and nineteenth century, cargo boats returning from Europe to North America would carry quarried stone as ballast, contributing to the architectural heritage of some east coast cities (for exampleMontreal), where this stone was used in building.[4] Stone ballast was also responsible for introducing hundreds of new plant species to North America.[5]
DuringWorld War 2 ships returning from Great Britain to the United States used rubble as ballast.[6] The ballast would be dumped in New York and used for construction projects such asFDR Drive and an outcrop colloquially named Bristol Basin since it was made from rubble from bombed-outBristol.[6]
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Ballast takes many forms, for example:
Sailing ballast is used insailboats to provide rightingmoment to resist the overturning moment generated by lateral forces on thesail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boatcapsizing. If a sailing vessel should need to voyage without cargo then ballast of little or no value would be loaded to keep the vessel upright. Some or all of this ballast would then be discarded when cargo was loaded.
Ballast weight is also added to arace car to alter its performance. In most racing series, cars have a minimum allowable weight. Often, the actual weight of the car is lower, so ballast is used to bring it up to the minimum. The advantage is that the ballast can be positioned to affect the car's handling by changing itsload distribution. This is near-universal inFormula 1. It is also common in other racing series that ballast may only be located in certain positions on the car. In some racing series, for example theBritish Touring Car Championship, ballast is used as a handicap, the leading drivers at the end of one race being given more ballast for the next race.
Ballast may also be carried aboard an aircraft. For example, ingliding it may be used to increase speed or adjust the aircraft's center of gravity, or in a balloon as abuoyancy compensator.