Flare

Flare is the outward slope of the side shell above the waterline, so the section widens with height and the deck edge overhangs the waterline beam. It adds reserve buoyancy and deck area high in the hull, throws spray and green water clear, and resists bow-down plunging, which is why it is concentrated forward as bow flare. Against that, flare raises the rate of buoyancy change as a section immerses, driving flare-slam impact pressures on fast or fine hulls that class rules treat as a forward shell design load. The opposite of flare is tumblehome, where the side falls inward above the waterline. Flare is a section property; sheer is the separate fore-and-aft sweep of the deck line.