Boat capsizing is a boating emergency which occurs when a boat tips over so far that it becomes unable to move. Classically, a boat must tip by 90 degrees or more to be considered capsized. The process of stabilizing a capsized boat and tipping it back into place is known as righting. If a boat actually flips over so that the keel is turned toward the sky, it has “turned turtle,” and it can be extremely difficult to get the boat righted again.
The smaller a boat is, the more likely boat capsizing will be, but large boats and even giant ships are not exempt. A wide variety of factors can cause a boat to capsize, including rough waves, high winds, and poor handling. Most boats can right themselves when they become 30 degrees or less off balance, because the weight of the ship is designed to promote an upright position. Some ships are capable of self-righting at more extreme angles, and these boats are often recommended for use by people who are just learning to sail, as they can be safer to handle.
When boat capsizing occurs, it poses a number of dangers. The craft could suffer severe structural damage, such as losing its mast or sections of the body, and it could potentially flood and sink, as for example when open portholes fill with water as the ship capsizes. Capsizing can also result in flooding of parts of the boat, which will be messy even if doesn't cause serious damage, and on boats with electronic components, boat capsizing could create a fault in the electrical systems.
It is possible to right a boat which has been capsized. Small boats like canoes and kayaks can often be righted by a single person, while larger craft may require the efforts of more people. Boating safety organizations sometimes recommend that people deliberately capsize their boats under supervision in safe, calm waters so that they can get an idea of what capsizing feels like, and how a particular boat handles, as each boat capsizes differently. Experiencing the event once can also make people feel more comfortable when it happens in an unplanned situation.
Some notable historic capsizings include that of the Andrea Doria in 1956, and the USS Oklahoma at Pearl Harbor in 1941. The fates of these large ships illustrate the fact that no craft is entirely immune to capsizing, and that all sailors can benefit from safety training so that they know what to do in a boat capsizing, and how to avoid conditions which can cause a boat to capsize.