Capsizing
Capsizing or keeling over occurs when a boat or ship is rolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it is upside down in the water.
Capsize may result from broaching, 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 not stable while inverted.
[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 of ship stability, immersibility and buoyancy involves other factors to address the relevant risks posed by waves, tides, weather and occurrences such as damage and collision.
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.
In 2012 the very large cruise ship Costa 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.
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 as in one of the largest peacetime maritime disasters when MS Estonia sank off of the Archipelago Sea in Finland), water entering the car-deck is subject to the free surface effect and may cause a capsize.
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.
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 turtle and then become extremely difficult to recover without assistance.
There is a wide range of technology that can be installed or strategically placed to prevent or deter a boat or ship from 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 the vessel's buoyancy and filling void space where water can collect, providing valuable time to remove the water, fix damage or evacuate.
There are three methods of making a vessel self-right: careful distribution of stationary weight and buoyancy, inflatable airbags, and movable ballast.
[11] Most small craft intended as lifeboats with rigid (rather than inflatable) hulls designed since about the middle of the twentieth century are self-righting.
