Capsizing

Capsizing or keeling over occurs when a boat or ship is turned on its side or it is upside down in the water. The act of reversing a capsized vessel is called righting.A crane capsizes a small coast guard vessel to test its righting abilityA larger self-righting vessel's stability test. Note large deckhouse, which is almost the only part submerged when fully inverted.The Beeching-Peake SR (self-righting) lifeboat won an 1851 competition for improved lifeboat design. Drawings show large, high buoyancy tanks, and ballast.The Lizzie Porter is a Peake-class lifeboat, an early design of self-righting boat. Note the high, rounded buoyancy tanks at her bow and stern, and low sides amidships. Capsizing or keeling over occurs when a boat or ship is turned on its side or it is upside down in the water. The act of reversing a capsized vessel is called righting. If a capsized vessel has enough flotation to prevent sinking, it may recover on its own if it is not stable inverted. Vessels of this design are called self-righting. In dinghy sailing, a practical distinction can be made between being knocked down (to 90 degrees) which is called a capsize, and being inverted, which is called being turtled. Small dinghies frequently capsize in the normal course of use and can usually be recovered by the crew. Some types of dinghy are occasionally deliberately capsized, as capsizing and righting the vessel again can be the fastest means of draining water from the boat. Capsizing (but not necessarily turtling) is an inherent part of dinghy sailing. It is not a question of 'if' but a question of 'when'. For those who do not want the experience, a keelboat monohull has physics on its side. But even yachts can capsize and turtle in extraordinary conditions, so design considerations are important. Such events can overcome skill and experience; boats need to be appropriate for foreseeable conditions. A capsized kayak may be righted with a roll or eskimo rescue. As long as the kayaker knows how to react, the water is not too shallow, and the location is not close to dangers that require evasive action by the kayaker – which cannot be taken while capsized – capsizing itself is usually not considered dangerous. In whitewater kayaking, capsizing occurs frequently and is accepted as an ordinary part of the sport. For sailing vessels, the 'capsize ratio' is a commonly published number used as a guideline for safe operation, where a ratio of less than 2.0 is considered suitable for offshore operation. However the only variables that go into 'capsize ratio' are a vessel's beam and its displacement, and a thorough assessment of ship stability needs to consider various other factors. In a storm, even large vessels may be rolled by being hit broadside by a large wave or 'pitchpoled' stem over stern in extreme waves. This is normally catastrophic for larger ships, and smaller yachts can be dismasted (i.e., lose their masts and rigging) due to the drag as the boat is forced to roll over. Among ship types, a roll-on-roll-off (RORO or ro-ro) ship is more prone to capsizing as it has large open car decks near the waterline. If the watertight car-deck doors fail through damage or mismanagement (as in the partial sinking of MS Herald of Free Enterprise where the doors were accidentally left open), and one of the largest peacetime maritime disasters when MS Estonia sank off of the Finnish archipelago, water entering the car-deck is subject to the free surface effect and may cause a capsize. As a RORO ferry rolls, vehicles can break free and slide down if not firmly secured, adversely altering the ship's centre of gravity, accelerating the roll, and possibly turning an otherwise recoverable roll into a capsize. A ship that is holed may capsize. In 2012 the very large cruise ship Costa Concordia was holed, lost its propulsion, and drifted into shallow water where she partially sank, resting on her side with most of her structure out of the water. Technically, this was not a capsize as her bottom was only partly exposed; rather this was a partial sinking.