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If a capsized vessel has enough flotation to prevent sinking, it may recover on its own if the stability is such that 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 which would 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. A ratio of less than 2.0 is considered suitable for offshore operation. The capsize ratio is only a guideline, since there are many factors involved in vessel stability.
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). Most small craft intended as lifeboats with rigid (rather than inflatable) hulls designed since about the middle of the twentieth century are self-righting.
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 capsize 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 the MS Herald of Free Enterprise, where the doors were accidentally left open), 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 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 and immediately sailed to nearby shallow water, where she 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.
A vessel which capsizes without being holed may allow water to enter in places normally above the waterline. The ship may not then be able to right herself; stability and safety will be compromised even if the vessel is righted.
In competitive yacht 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 have turned turtle or turtled. Good racers can often recover from a capsize with minimal loss of time.
Motor life boats are designed to be self-righting if capsized but most other motorboats are not.
Intermediate sailors are encouraged to capsize their dinghy in a safe location with supervision at least once to become acquainted with their boat's floating properties and the capsize process. The boat should then be 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 self recover.
Most small monohull sailboats can normally be righted by standing or pulling down on the centreboard, daggerboard (or bilgeboard in a Scow) to lift the mast clear of the water. Depending on the design of the hull, the boat's righting moment will normally take effect once the mast is around 30 degrees from horizontal and help pull the boat vertical. 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 small catamarans such as the Hobie 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 will turn turtle and then become extremely difficult to recover without assistance. See Turtling. Some monohulls and catamarans may 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). See Turtling.
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. The bow 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 should be 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.
Bermuda rigged sailing boats are vulnerable to lee waves. In the worst case lee waves appear behind high islands. For example, in the Adriatic Sea (Dalmatia) or the Aegean Sea (Greece) relatively small islands can be very high and have a good steady wind such as the Meltemi/Etesian in the Aegean during the dry summer season. The direction of the wind on the lee side of the island may be downwards, and this is feared because it causes instability in controlling the boat and in the worst case pushes the sail under water, which can lead to disastrous capsizing. This is not possible with ordinary winds, because the push of an ordinary wind in a sail disappears when the sail becomes horizontal. Many use the expression downburst for this extreme sailing weather condition, but it is certainly more related to lee waves.
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