A chine is an angular meeting of hull sections, such that they form a noticable angle. A prominant angle is known as a hard chine, while a rounded angle is known as a soft chine. The term is not typically used for the turn of the transom, deck edge, or stem line.
Chines may sure aesthetic, constructibility, or performance benefits.
Chines produce a prominent line. When placed above the waterline, they can be used to breakup a large slab side, or to insinuate contours which the hull otherwise does not possess. Angular chines are sometimes used to give a menacing or futuristic look to yachts.
Chines allow for disparate hull surfaces to be brought together while remaining developable. Many designs exist which are of exclusively flat panels, such as a plywood scow. These vessels feature hard chines to reduce or remove the need to work the material. On some larger vessels, particularly those which use thick steel plates (such as some icebreakers), a facetted hull of flat panels have been used to reduce cost and man-hours. In the case of icebreakers, open-water efficiency is considered secondary to slow-speed performance in thick ice, where the effect of the facetted hull is mitigated or offset by the initial build cost and savings in terms of plate renewal over the vessels lifetime.
Chines can be considered as a round bilge with a minimal or zero radius. In this scenario, a chine can be used to increase the displacement and carrying capacity of a vessel without increasing any of its primary dimensions. A hard chine near the bottom of the hull can also be used to enlarge the size of flat panel which can be created on the hulls underside, promoting planing on high-speed vessels. Chines can also be used to introduce a purposeful discontinuity designed to disrupt or redirect the flow of water away the hull, such as in an integrated spray rail.