In dinghy sailing, a boat is said to be turtling or to turn turtle when the boat is fully inverted with the mast pointing down to the lake bottom, riverbed, or seabed. The name stems from the appearance of the upside-down boat, similar to the carapace (top shell) of a sea turtle. The term can be applied to any vessel; turning turtle is less frequent but more dangerous on ships than on smaller boats. It is rarer but more hazardous for multihulls than for monohulls, because of multihulls are harder to flip in both directions. Measures can be taken to prevent a capsize (where the boat is knocked over on its beam-ends but not yet inverted) from becoming a turtle (with bottom up). Definition and prevention When a boat is "turned over completely" it has turned turtle. Some sources treat the term "turtle" as synonymous with "capsize" or "keel over". but most others make a distinction. Carrying too much sail or loss of control can lead to broachingthe boat heels too far to one side, or capsizes. While all turtlings involve a capsize, the converse is untrue. Prevention is the first priority. With the exception of self-righting watercraft, vessels have an angle of vanishing stability (AVS). External forces aside, if they are tilted at an angle less than the AVS, they will pop back upright. If they are tilted at an angle greater than the AVS, they will turn turtle and stay there. In other words, non-self-righting vessels are stable when turtled. Their primary stability and secondary stability are greater than zero, tending to right them, but their tertiary or inverted stability is less than zero, and tends to keep them upside-down. Capsizing (but not necessarily turtling) is an inherent part of dinghy sailing, and is considered to be "routine". It is not a question of "if" but a question of "when". For those who prefer to avoid the experience, a keelboat monohull has physics on its side. (See limit of positive stability.) But even yachts can capsize and turtle in extraordinary conditions, so design considerations and suitability for particular tasks, locations, weather, duration and situations are essential queries. "Such events can overcome skill and experience"; boats need to be appropriate for foreseeable conditions. It is a fundamental question of seaworthiness. Turtling commonly occurs when a boat capsizes and is not righted or attended to in time, allowing it to