Shipwrecking

For the wreck of a ship, see Shipwreck.
Shipwrecked people on an improvised raft.

Shipwrecking is the event that caused the wreck, such as the striking of something that causes the ship to sink, the stranding of the ship on rocks, land or shoal, or the destruction of the ship at sea by violent weather. This article will deal mainly to the event and its causes.

According to one scientist who studies rogue waves, "two large ships sink every week on average, but the cause is never studied to the same detail as an air crash. It simply gets put down to 'bad weather'."[1]

Causes

Factors for the loss of a ship may include:

Design and equipment failure

The hallmark of a shipwreck due to poor design is the capsize of Swedish warship Wasa in Stockholm harbour 1628. She was too narrow, had too little ballast and her lower cannon deck had too low free-board for good seaworthiness. Poor design allowed the ferry MS Herald of Free Enterprise to put to sea with open roll-on/roll-off bow doors, with tragic consequences. Failure or leaking of the hull is a serious problem that can lead to the loss of buoyancy or the free surface effect and the subsequent sinking of the vessel. Even the hulls of large modern ships have cracked in heavy storms. Leaks between the hull planks of wooden vessels are a particular problem.

Equipment failure caused the shipwreck of cruiseferry Estonia in 1994. The stress of stormy seas on hull and bow especially caused the bow visor to break off, in turn tearing the watertight bow door open and letting seawater flow onto the car deck. She capsized with tragic consequences. Failure of pumps can lead to the loss of a potentially salvageable ship with only a minor leak or fire.

Failure of the means of propulsion, such as engines, sails or rigging, can lead to the loss of a ship. When the ship's movement is determined only by currents or the wind and particularly by storms, a common result is that the ship is unable to avoid natural hazards like rocks, shallow water or tidal races. Loss of propulsion or steering can inhibit a ship's ability to safely position itself in a storm, even far from land. Waves attacking a ship's side can overwhelm and sink it.

Instability and foundering

Instability is caused by the centre of mass of the ship rising above the metacenter resulting in the ship tipping on its side or capsizing, which is often referred to as foundered or foundering. This can lead to a sinking if the openings on the upper 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 (known as downflooding). 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 ventilation to compartments, including the engine room, for crew access, and to load and unload cargo.

Bad weather

Ivan Aivazovsky's The Ninth Wave painting shows a handful of survivors clinging to the mast of a sunken ship.

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:

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 can cause instability by accumulating high on the ship, or in severe cases, crush the hull if the ship becomes trapped in a freezing sea.

Fire

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 (e.g. Cospatrick). The detonation of cargo or ammunition can cause the breach of a steel hull. An extreme temperature may compromise the durability properties of steel, causing the hull to break on its own weight. Often a large fire causes a ship to be abandoned and left to drift (e.g. MS Achille Lauro). Should it run aground beyond economic salvage, it becomes a wreck.

In extreme cases, where the ship's cargo is either highly combustible (such as oil, natural gas or gasoline) or explosive (nitrates, fertilizers, ammunition) a fire onboard may result in a catastrophic conflagration or explosion. Such disasters may have catastrophic results, especially if the disaster occurs in a harbour, such as the Halifax Explosion.

Navigation errors

Shipwreck of SS Harvard on Point Arguello, California, 1931

Many shipwrecks have occurred when the crew of the ship allowed the ship to collide with rocks, reefs, icebergs, or other ships. Collision has been one of the major causes of shipwreck. 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 20th century, the most sophisticated navigational tools and techniques available - dead reckoning using the magnetic compass, marine chronometer (to calculate longitude) and ships logbook (which recorded the vessel's heading and the speed measured by log) or celestial navigation using marine chronometer and sextant - were sufficiently accurate for journeys across oceans, but these techniques (and in many cases also the charts) lacked the precision to avoid reefs close to shore.

The Scilly naval disaster of 1707, which claimed nearly 2,000 lives and was one of the greatest maritime disasters in the history of the British Isles, is attributed to the mariner's inability to find their longitude. This led to the Longitude Act to improve the aids available for navigation. Marine chronometers were as revolutionary in the 19th century as GPS is today. However the cost of these instruments could be prohibitive, sometimes resulting in tragic consequences for ships that were still unable to determine their longitude, as in the case of the Arniston.

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 data. 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.

Over the centuries, many technological and organisational developments have been used to reduce accidents at sea including:

See also

References

  1. ↑ "Ship-sinking monster waves revealed by ESA satellites". European Space Agency. July 21, 2004. Archived from the original on July 24, 2014.

Further reading

External links

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