Editing Capsizing (section)

==Self-righting==
<gallery mode="packed" heights="300px">
File:Coast Guard response boat-small DVIDS1076833.jpg|A [[crane (construction)|crane]] capsizes a small coast guard vessel to test its righting ability
File:Eiswette(II) 20080627 Kentertest diff.gif|A larger self-righting vessel's stability test. Note large deckhouse, which is almost the only part submerged when fully inverted.
File:Northumberland model lifeboat.JPG|The [[James Beeching|Beeching]]-[[James Peake (shipwright)|Peake]] SR (self-righting) lifeboat won an 1851 competition for improved lifeboat design. Drawings show large, high buoyancy tanks, and ballast.
File:RNLI Chatham Lizzie Porter Holy Island 8352.JPG|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.
</gallery>

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). The [[angle of vanishing stability]], the angle of [[Heeling (sailing)|heel]] 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.<ref name="A&S">{{cite journal |last=Akyıldız |first1=Hakan |last2=Şimşek |first2=Cemre |title=Self-righting boat design |journal=GiDB-DERGi |date=2016 |issue=6 |pages=41–54 |url=http://gidbdergi.itu.edu.tr/sayilar/06/0604.pdf |access-date=21 June 2019 |archive-date=23 September 2019 |archive-url=https://web.archive.org/web/20190923093738/http://gidbdergi.itu.edu.tr/sayilar/06/0604.pdf |url-status=dead }}</ref>

A basic tool for calculating a vessel's stability is a static stability diagram, which plots the angle of [[Heeling (sailing)|heel]] on the horizontal axis and the righting lever (GZ) on the vertical axis. (see [[metacentric 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.<ref name="A&S"/> See also [[primary stability]] and [[secondary 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.<ref name="A&S"/>

Most small craft intended as [[lifeboat (rescue)|lifeboats]] with rigid (rather than inflatable) hulls designed since about the middle of the twentieth century are self-righting.{{citation needed|date=February 2014}}

Small radio-controlled boats may also self-right. This is particularly useful for racing.<ref>{{cite web |title=Best Self Righting RC Boat: Top Picks for 2019 |url=https://rchobbyreview.com/self-righting-rc-boat/ |website=Radio-controlled hobby review |date=21 September 2018 |access-date=21 June 2019 |archive-date=21 June 2019 |archive-url=https://web.archive.org/web/20190621033957/https://rchobbyreview.com/self-righting-rc-boat/ |url-status=dead }}</ref>