S-frame

The underwater hull of an older sailing yacht ( long keeler) shows the typical S-shaped frame

S-Spant describes a hull shape typical of classic sailing yachts , which has hull halves delimited in an S-shape in cross-section.

Under the bulging outward curve, the hull of the underwater hull curves in towards the keel with an opposite curvature. Any transverse ribs therefore run in an S shape. Yachts with an S-shaped frame are always long keelers or moderate long keelers, short keelers have other frame shapes.

Boats with an S-bulkhead

Folk boat , archipelago cruiser etc.