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 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 rolling, tertiary stability, or the stability of an upside-down kayak, is also important (lower tertiary stability makes rolling up easier).
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 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 rolling, tertiary stability, or the stability of an upside-down kayak, is also important (lower tertiary stability makes rolling up easier).