Hull Shapes

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The hull shape of a sailing boat largely determines its handling characteristics, its directional stability, and its suitability for the intended use. Hulls are distinguished by the number of hulls and by the cross-section of the underwater body.

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Number of Hulls

Monohull

A single-hull boat that draws its stability either from a ballast keel or from the crew's weight (dinghy).

Catamaran

Two parallel hulls connected by a deck or trampoline. Catamarans are fast at low heel angles and offer plenty of deck space. After a capsize they are difficult to right.

Trimaran

A main hull with two smaller side hulls (floats). Trimarans combine the speed of a multihull with better balance than a catamaran.

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Cross-Section of the Underwater Body

Round Bilge with Fin Keel

A round, harmonic underwater profile with a separate fin keel. The most common shape on modern sailing yachts. The keel offers a high righting moment with little wetted surface.

Hard Chine

A hull with a sharp transition (chine) between bottom and topsides. Easy to build and offers good form stability, but produces more turbulence underwater than a round bilge.

Round Bilge with Twin Keels

A round-bilge hull with two laterally offset keels. Allows the boat to take the ground upright in tidal areas.

Round Bilge with S-Curve

A round bilge with an S-shaped curve in the cross-section. Offers a good compromise between displacement and stability.

V-Bottom

A pronounced V-shaped underwater body. Cuts well through waves at high speed and is therefore common on motor and sport boats.

Flat Bottom

A flat underwater body. Offers high form stability and shallow draft but is sensitive to wind and waves.

Round-Bilge Dinghy

A round-bilge dinghy with centreboard. Sporty handling and forgiving behaviour at the limit.