In British usage, a shipwreck is the remains of a ship after it has sunk or been beached as a result of a crisis at sea. In American usage, shipwreck also refers to the event that caused the damage or destruction of the ship.
Ships are lost for many reasons, including:
failure of the ship's equipment
warfare and piracy
Failure or leaking of the hull is a serious problem that can lead to the loss of buoyancy and the sinking of the vessel. Even the hulls of large modern ships have cracked in heavy storms. Leaks between the hull planks of wooden vessels was a particular problem.
Failure of the means of propulsion, such as engines, sails or rigging, can lead to the loss of a ship. A common problem is that the ship is unable to avoid natural hazards like rocks, shallow water or storms.
Instability is caused by the centre of mass or other forces acting on the ship rising above the centre of buoyancy resulting in the ship tipping on its side or capsizing.
This can lead to a sinking if the openings on the upper side of the side are not watertight at the time of the capsize. To remain buoyant, the hull of a vessel must prevent water entering the large air spaces of the vessel. Clearly for the ship to float, the submerged parts of the hull will be watertight, but the upper parts of the hull must have openings to allow the crew to work and to load and unload cargo.
Many shipwrecks have occurred when the crew of the ship allowed the ship to collide with rocks, reefs or other ships. Accurate navigation is made more difficult by poor visibility in bad weather. Also, many losses happened before modern navigation aids such as GPS, radar and sonar were available. Until the twentieth century, the most sophisticated navigational tools and techniques available, dead reckoning using the magnetic compass, chronometer and sextant were rather inaccurate.
Even today, when highly accurate navigational equipment is readily available and universally used, there is still scope for error. Using the incorrect horizontal datum for the chart of an area may mislead the navigator, especially as many charts have not been updated to use modern datums. It is also important for the navigator to appreciate that charts may be significantly in error, especially on less frequented coasts. For example, a recent revision of the map of South Georgia in the South Atlantic showed that previous maps were in some places in error by several kilometres!
Poor weather can cause several problems:
Wind causes waves which result in other difficulties. Waves make navigation difficult and dangerous near shallow water. Also, waves create buoyancy stresses on the structure of a hull. The weight of breaking waves on the fabric of the ship force the crew to reduce speed or even travel in the same direction as the waves to prevent damage. Also, wind stresses the rigging of sailing ships.
The force of the wind pushes ships in the direction of the wind. Vessels with large windage suffer most. Although powered ships are able to resist the force of the wind, sailing vessels have few defences against strong wind. When strong winds are imminent, sailing vessels typically have several choices:
try to position themselves so that they cannot be blown into danger
shelter in a harbour
anchor behind a sheltering landform
Many losses of sailing ships were caused by sailing, with a following wind, so far into a bay that the ship became trapped upwind of a lee shore, being unable to sail into the wind to leave the bay.
Low visibility caused by fog, mist and heavy rain increase the navigator's problems.
Cold can cause metal to become brittle and fail more easily. A build-up of ice high on the ship can cause instability.
Warfare, piracy and mutiny have also led to the loss of many ships.
Typical weapons used to sink ships have been: guns, fire, torpedoes, depth charges, mines and bombs.
Examples of the use of violence to sink civilian ships include the commerce raiding, unrestricted submarine warfare and tonnage war.
Fire can cause the loss of ships in many ways. The most obvious way would be the loss of a wooden ship which is burned until watertight integrity is compromised. The detonation of cargo or ammunition can cause the breach of a steel hull. Often a large fire causes a ship to be abandoned and left to drift. Should it run aground beyond economic salvage, it becomes a wreck. In certain cases, the use of seawater to extinguish a fire results in loss of buoyancy as was the case of the liner SS Normandie.
Prevention of shipwrecks
Over the centuries, many technological and organisational developments have been used to reduce accidents at sea including:
pilotage aids including lighthouses and sea marks
basic navigation tools such as the magnetic compass, nautical chart, chronometer, sextant, log
advanced navigation tools such as the radio communication, gyrocompass, sonar, hyperbolic radio navigation and satellite navigation
inspection of shipbuilding quality and maintenance of seaworthiness of the ship such as "A1 at Lloyd's"
State of preservation
Many factors determine the state of preservation of a wreck:
the ship's construction materials
the level of destruction involved in the ship's loss
whether the components or cargo of the wreck were salvaged
whether the wreck was demolished to clear a navigable channel
the depth of water at the wreck site
the strength of tidal currents at the wreck site
the exposure to surface weather conditions at the wreck site
the presence of marine animals that consume the ship's fabric
the salinity of the water the wreck is in
extreme cold (such as a glacial-fed lake) can slow degredation of organic ship materials
Exposed wooden components decay quickly. Often the only wooden parts of wooden ships that remain after a century are those that were buried in silt or sand soon after the sinking. An example of this is the Mary Rose.
Steel and iron, depending on its thickness, may retain the ship's structure for decades. As corrosion takes place, sometimes helped by tides and weather, the structure collapses. Thick ferrous objects like cannons, steam boilers or the pressure vessel of a submarine often survive well underwater in spite of corrosion.
Propellers, condensers, hinges and port holes were often made from non-ferrous metals such as brass and phosphor bronze, which do not corrode easily in water.
• Database of 10,000 submerged wrecks and obstructions in the coastal waters of the United States
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