Capsizing

Capsizing (or keeling over) is when a boat or ship is turned on its side or it is upside down. 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 the stability is such that it is not stable inverted. Vessels of this design are called self-righting.

Small vessels

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.