Editing Kayak (section)

==== Types of stability ====
{{main|primary stability|secondary stability|tertiary stability}}
[[File:Chines.svg|thumb|upright=2.5|Hypothetical cross-sections of kayaks. Left to right: High primary stability but low secondary stability, lower primary stability but ~same secondary stability, lower primary but higher secondary stability, two extra chines, four extra chines. More [[chine (boating)|chines]] (angles) give a more rounded profile, decreasing stability, tracking, and the [[wetted area]], and increasing speed.|alt=1) a five-sided polygon which is nearly a wide rectangle, with the lower long side (the boat's bottom) a bit shorter than the upper (the deck) and the fifth point (the keel) slightly bending the nearly-flat bottom downwards. 2) The short sides retain the same angle, but the keel is a bit lower and the chines a bit higher. 3) The chines are substantially closer together and higher than the keel so that the angles of the hull at the chines and at the keel are all three approximately equal. 4) Two additional chines make a seven-sided polygon which approximates a half-circle with the flat side up. 5) A 9-sided polygon approximating a half-circle more closely.]]
''Primary'' (sometimes called ''initial'') stability describes how much a boat tips, or rocks back and forth when displaced from level by paddler weight shifts. ''Secondary'' stability describes how stable a kayak feels when put on edge or when waves are passing under the hull perpendicular to the length of the boat. For [[kayak roll]]ing, ''tertiary'' stability, or the stability of an upside-down kayak, is also important (lower tertiary stability makes rolling up easier).{{citation needed|date=May 2021}}

Primary stability is often a big concern to a beginner, while secondary stability matters both to beginners and experienced travelers. By example, a wide, flat-bottomed kayak will have high primary stability and feel very stable on flat water. However, when a steep wave breaks on such a boat, it can be easily overturned because the flat bottom is no longer level. By contrast, a kayak with a narrower, more rounded hull with more [[flare (ship)|hull flare]] can be edged or leaned into waves and (in the hands of a skilled kayaker) provides a safer, more comfortable response on stormy seas. Kayaks with only moderate primary, but excellent secondary stability are, in general, considered more [[Seakeeping|seaworthy]], especially in challenging conditions.

[[File:West Greenland kayak cross-section after Nansen.svg|thumb|A cross-section through a skin-on-frame kayak. The skin touches only at the two [[gunwales]], the two [[strake|stringers]], and the [[keel]].]]
The shape of the cross section affects stability, maneuverability, and drag. Hull shapes are categorized by roundness, flatness, and by the presence and angle of [[Chine (boating)|chine]]s. This cross-section may vary along the length of the boat.

A chine typically increases secondary stability by effectively widening the beam of the boat when it heels (tips). A V-shaped hull tends to travel straight (track) well but makes turning harder. V-shaped hulls also have the greatest secondary stability. Conversely, flat-bottomed hulls are easy to turn, but harder to direct in a constant direction. A round-bottomed boat has minimal area in contact with the water, and thus minimizes drag; however, it may be so unstable that it will not remain upright when floating empty, and needs continual effort to keep it upright. In a skin-on-frame kayak, chine placement may be constrained by the need to avoid the bones of the pelvis.<ref name=antropometric_measurements>{{cite web|url=http://www.kayakways.net/kayaksandpaddles/kayakfitting/|title=kayakways.net – Kayak Fitting|website=Kayakways.net|access-date=November 29, 2017|archive-date=February 24, 2020|archive-url=https://web.archive.org/web/20200224060810/http://www.kayakways.net/kayaksandpaddles/kayakfitting|url-status=dead}}</ref>

[[Sea kayak]]s, designed for open water and rough conditions, are generally narrower at {{cvt|22|-|25|in|cm|order=flip|round=5}} and have more secondary stability than recreational kayaks, which are wider {{cvt|26|-|30|in|cm|order=flip|round=5}}, and have a flatter hull shape and more primary stability.<ref>{{Cite web |date=June 10, 2021 |title=Touring vs Recreational Kayaks - Brooklyn Kayak Company |url=https://brooklynkayakcompany.com/blogs/our-blog-2/recreational-vs-touring-kayaks |access-date=October 10, 2023 |website=brooklynkayakcompany.com}}</ref><ref>{{Cite web |title=Types of kayaks |url=https://www.mec.ca/en/explore/about-kayaks |access-date=October 10, 2023 |website=MEC |language=en}}</ref>