Capsizing orkeeling over occurs when aboat orship isrolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it isupside down in the water. The act of recovering a vessel from a capsize is calledrighting. Capsize may result frombroaching,knockdown, loss of stability due to cargo shifting or flooding, or in high speed boats, from turning too fast.
If a capsized vessel has enough flotation to prevent sinking, it may recover on its own in changing conditions or through mechanical work if it is notstable while inverted. Vessels of this design are calledself-righting.
Indinghy sailing, a practical distinction can be made between being knocked down (to 90 degrees; on itsbeam-ends, figuratively) which is called a capsize, and being inverted, which is called beingturtled. 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.[citation needed]
Capsizing (but not necessarily turtling) is an inherent part of dinghy sailing. Many have described it as "not a question of 'if' but a question of 'when'."[1] For those who do not want the experience, akeelboatmonohull has physics on its side.[1][2] But evenyachts can capsize and turtle in extraordinary conditions, so design considerations are important.[2] Such events can overcome skill and experience; boats need to be appropriate for foreseeable conditions.[3]
A capsizedkayak may be righted with aroll oreskimo 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. Inwhitewater kayaking, capsizing occurs frequently and is accepted as an ordinary part of the sport.[citation needed] Kayak rolling, in which paddlers intentionally capsize and right themselves (in synchrony, as many times as possible in a given interval, or in as many different ways as possible) is also a competitive sport, especially in Greenland.[citation needed]
Sailing vessels' "capsize ratio" is commonly published as a guideline for zones of safe operation — less than 2.0 means as a rule-of-thumb suitability for offshore navigation. However its crude nature of displacement divided by a vessel's beam (breadth) (albeit with a constant multiplied to provide an average assessment), means thorough assessment ofship stability, immersibility and buoyancy involves other factors to address the relevant risks posed by waves, tides, weather and occurrences such as damage and collision.[citation needed][clarification needed]
In a storm, even large vessels may be rolled by being hit broadside by a large wave or swell or "pitch poled"stem overstern in extremewaves. This is normally catastrophic for larger ships, and smaller yachts can be dismasted (i.e., lose theirmasts andrigging) due to the drag as the boat is forced to roll over.
A ship that sustains a hole or crack ('is holed') may capsize.[4] This is the working oftorpedo andnaval mine warfare. In 2012 the very largecruise shipCosta Concordia was holed and lost her propulsion by striking a charted rock, and drifted further where she partially sank just outside the harbor entrance, coming to rest with her starboard side submerged and resting on the seafloor with approximately two-thirds of her structure above the sea. This was not a capsize as her bottom was only partly exposed; rather this was a partialsinking. Fixing a hole is called plugging.
Otherwise a vessel in largely upright position which capsizes has suffered too much water to enter in places normally above the waterline, and which may be caused by poor manoeuvering, overloading (seePlimsoll Line) or poor weather. As for holes, bailing may be carried out – removal of water aboard such as with abilge pump,self or hand bailer, buckets or de-watering pumps. At the stage of sinking where its buoyancy is deemed critical, the ship is unlikely to upright nor able to right itself such that stability and safety will be compromised even if the vessel is righted – a decision is made to abandon ship and any ultimate salvage may entail firm grounding and re-buoyancy pumps. Among ship types, aroll-on-roll-off (RORO or ro-ro) ship is more prone to capsizing as it has large open car decks near thewaterline. If the watertight car-deck doors fail through damage or mismanagement (as in the partial sinking ofMS Herald of Free Enterprise where the doors were accidentally left open, and as in one of the largest peacetime maritime disasters whenMS Estonia sank off of theArchipelago Sea in Finland), water entering the car-deck is subject to thefree surface effect and may cause a capsize. As a RORO ferryrolls, vehicles can break free and slide down if not firmly secured, adversely altering the ship'scentre of gravity,accelerating the roll, and possibly turning an otherwise recoverable roll into a capsize.
In competitiveyacht racing, a capsized boat has certain special rights as it cannot maneuver. A boat is deemed capsized when the mast is touching the water; when it is fully inverted, it is said to haveturned turtle or turtled.[5] Good racers can often recover from a capsize with minimal loss of time.
The capsize can result from extremebroaching, especially if thekeel has insufficient leverage to tilt the vessel upright.
Somerescue lifeboats, for example theRNLI'sSevern class, are designed to be self-righting if capsized, but most other motorboats are not.[citation needed]
Intermediate sailors are encouraged to capsize their dinghies in a safe location with supervision at least once to become acquainted with their boat's floating properties and the capsize process. The boat is then righted, bailed out, and the sails reset, so that in the event of an uncontrolled capsize, the boat and its occupants are familiar with the procedure and may recover.
Most small monohull sailboats can normally be righted by standing or pulling down on thecentreboard,daggerboard (orbilgeboard in ascow) to lift the mast clear of the water. Depending on the design of thehull, the boat'srighting moment will normally take effect once the mast is around 30 degrees from horizontal and help pull the boatvertical. Righting a catamaran that is lying on its side involves using a righting line fed over the upper hull. The crew stands on the lower hull and pulls back on the righting line. In smallcatamarans such as theHobie 16 it is imperative that at least one crew member assumes this task as soon as possible as there is a chance that the boat willturtle and then become extremely difficult to recover without assistance.[6] Somemonohulls and catamarans use a small flotation device mounted at the tip of the mast or mainsail to ensure that the craft cannot assume an inverted position, or at least that a fully inverted position is not stable (i.e. it would come to a position where the mast is lying on the surface of the water, which would be preferable to fully inverted).
In both cases, having a crew member lift the end of the mast out of the water may help speed the process, as the greatest challenge of righting a capsized boat is shedding the weight of the water from the sails. A helpful step, where possible (on a loose footed sail), is to disconnect the clew of the sail from the boom, which prevents the sail from scooping up water as the sail lifts out of the water. Thebow of the capsized vessel should be pointed towards the wind so that when the sail starts to lift out of the water the wind can catch underneath the sail and help right the boat.
Care is taken not to let the boat swing all the way over and capsize on the other side, frequently with the crew on the bottom. This is more likely if the boat is not pointed into the wind.
There is a wide range of technology that can be installed or strategically placed to prevent or deter a boat or ship from capsizing. The various technologies rely on inflating airbags also known as lift bags which increasing the vessel'sbuoyancy with the water. There are many steps a crew can take to reduce the chance of capsizing, such as distributing the weight evenly and taking care during windy weather.[7]
Capsizing in yachts can occur when water is able to infiltrate the hull and decrease the vessels water and buoyancy leading to capsizing. Yachts can be deployed with a flotation system which is a series of strategically placed lift bags within the interior of the hull increasing thevessel's buoyancy and filling void space where water can collect, providing valuable time to remove the water, fix damage or evacuate.[8]
When larger ships such as cargo ships and tankers capsize or sink not only is recovery not possible but greatenvironment damage can occur from spillage of cargo.[9] Larger ships are being equipped with Surfacing System for Ship Recovery which is an inflatable device that is installed in theballast water tank or within the hull of the vessel and can be deployed within seconds of an accident to stabilize the vessel and give more time for rescue and evacuation.[10]
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A vessel may be designated as "self-righting" if it is designed to be able to capsize then return to upright without intervention (with or without crew on board). Theangle of vanishing stability, the angle ofheel at which a vessel becomes unstable and does not bob back upright, does not exist; a self-righting boat will return to upright from any position, including completely upside-down. A self-righting vessel must be positively buoyant when swamped. There are three methods of making a vessel self-right: careful distribution of stationary weight and buoyancy, inflatable airbags, and movable ballast.[11]
A basic tool for calculating a vessel's stability is a static stability diagram, which plots the angle ofheel on the horizontal axis and the righting lever (GZ) on the vertical axis. (seemetacentric height for details). If the static stability curve never crosses the x-axis, the boat is not stable upside-down. This is not sufficient to build a boat with good stability at sea, as it neglects the effects of wind, waves, and human occupants, but it is a simple, powerful way to analyze the stability of a vessel.[11] See alsoprimary stability andsecondary stability.
Self-righting through distribution of weight and buoyancy requires the weight low-down, and the buoyancy high up. It is often accomplished with a self-sealing superstructure, such as the large deckhouses on modern rescue boats.[11]
Most small craft intended aslifeboats with rigid (rather than inflatable) hulls designed since about the middle of the twentieth century are self-righting.[citation needed]
Small radio-controlled boats may also self-right. This is particularly useful for racing.[12]
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