A pirate ship or galleon could be wrecked in a number of ways, besides being sunk in battle. A ship could become overbalanced by badly loaded cargo. Its top-heavy shape could make it topple over in the wind. Storms could whip up massive waves that swamped it with water. In tropical regions, hurricanes, which cause high winds and mountainous waves, were an ever-constant threat. Sharp coral reefs or rocks just below the water’s surface could smash a hole in a ship's hull, causing water to flood in. Sometimes, shipwrecked sailors could make their escape in rowing boats or on makeshift rafts. But many drowned for one simple reason: very few sailors could swim.

Rotting wrecks

Ocean currents would usually cover much of a wrecked ship in a layer of sediment—sand, silt and mud. Beneath this layer there was no oxygen, so materials such as cloth, wood or leather, which would otherwise rot away or be eaten by marine worms, were preserved. Eventually the entire shipwreck was likely to be covered in layers of sediment. Only perhaps a few pottery jars and some metal objects such as a cannon, treasure chest and the ship’s anchor would remain above the seabed.
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If a galleon sank in the region of a coral reef, it might gradually become part of the reef itself, teeming with life. Old iron anchors and cannon are perfect objects for coral to grow around. They may gradually became encrusted with coral and the shells of tiny sea creatures.

​​​​​​​Rust, formed by seawater reacting with objects made of iron, builds up on objects such as the anchor and treasure chest. Concretions, lumps of rust that grow bigger and bigger, start to form.

Even with modern-day diving equipment, divers are not able to swim down to very deep wrecks. They risk getting “the bends”—bubbles of nitrogen that form in the blood when deep-water divers rise to the surface.­ At great depths, their bodies could also be crushed by the pressure of the water. Instead, up to two divers can use a small under­water vehicle called a submersible. Submersibles have thick walls to withstand the water pressure. They are equipped with lights, cameras and often a long arm, controlled by the crew, that can pick up objects from a wreck. Propellers help to move the submersible in all directions.

Studying shipwrecks

Once items from a shipwreck are brought to the surface, conserving work begins. Stone or glass may just need to be cleaned, but materials such as cloth, leather and wood are treated with chemicals to prevent them from breaking apart as they dry out.

Sometimes the timbers of the ship itself are raised. Special lifting equipment must be used to support every part of the ship. Once out of the water, the ship must be continually sprayed with water and a waxy chemical called PEG, a process that can take years.