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Shellfish
Designer: Francois Sergent  ·  Builder: Cnso (Fra)  ·  First built: 1965
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About the Shellfish

Designed by François Sergent and first launched in 1965, this French-built sailboat represents classic European craftsmanship from the golden era of wooden boat construction. The Shellfish emerged during a period when designers were transitioning from traditional full-keel configurations to more modern fin-keel designs, evident in its fin keel with rudder on skeg arrangement. With its moderate displacement of 4,850 pounds and substantial ballast ratio, the Shellfish strikes a balance between performance and stability that makes it well-suited for coastal cruising and weekend sailing. The masthead sloop rig provides straightforward sail handling, while the boat's dimensions create a comfortable interior for its size class. Built by CNSO in France, these boats showcase traditional wooden construction techniques that were hallmarks of French boatbuilding in the 1960s. The design's comfort ratio of 17.74 indicates a relatively stiff, quick-motion boat that responds well in varying conditions, while the capsize screening value of 1.94 suggests good stability characteristics for coastal waters. With a hull speed of 6.60 knots and sail area-to-displacement ratio of 19.32, the Shellfish offers respectable performance for cruising sailors who appreciate classic wooden boat character with modern underwater design elements.

Core Dimensions
LOA (Length Overall) 28.71 ft / 8.75 m
LWL (Waterline Length) 24.28 ft / 7.40 m
Beam 8.20 ft / 2.50 m
Max Draft 4.59 ft / 1.40 m
Displacement 4,850.00 lb / 2,200 kg
Ballast 1,764.00 lb / 800 kg
Ballast Type Cast iron
Sail Area (Reported) 344.98 ft² / 32.05 m²
Design & Construction
Hull Type Fin with rudder on skeg
Rigging Type Masthead Sloop
Construction Wood
Designer Francois Sergent
Builder CNSO (FRA)
First Built 1965
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Performance Ratios
SA/Displacement Sail Area to Displacement ratio measures how much sail power a boat has relative to its weight. Higher values mean more performance and speed.
Under 14 — Heavy cruiser, slow14–18 — Cruising sailboat18–22 — Cruiser/racerOver 22 — Performance racer
 19.32
Ballast/Displacement Ballast to Displacement ratio shows what percentage of the boat's total weight is ballast. Higher values generally mean better initial stability and stiffer sail carrying.
30–35% — Typical cruiser35–45% — Stiff performance boatOver 45% — Racing oriented
 36.36
Displacement/Length Displacement to Length ratio measures how heavy a boat is relative to its waterline length. Lower values mean a lighter, faster boat.
Under 100 — Ultralight racer100–200 — Light cruiser/racer200–300 — Moderate cruiser300–400 — Heavy cruiserOver 400 — Very heavy
 151.31
Comfort Ratio Ted Brewer's Comfort Ratio predicts how comfortable a boat will feel in offshore conditions. Higher values mean a steadier, more comfortable motion in a seaway.
Under 20 — Uncomfortably rough20–30 — Acceptable coastal30–40 — Good offshore comfortOver 40 — Very comfortable offshore
 17.74
Capsize Screening Formula The USHS Capsize Screening Formula estimates offshore capsize risk. Lower is safer — values under 2.0 are considered acceptable for offshore sailing.
Under 2.0 — Safe for offshore2.0–2.2 — Borderline offshoreOver 2.2 — Coastal use recommended
 1.94
Hull Speed Hull Speed is the theoretical maximum speed of a displacement hull, calculated from waterline length. Most cruising sailboats reach this speed in moderate conditions. 6.60 kn
Pounds/Inch Immersion Pounds per Inch Immersion (PPI) tells you how much weight is needed to sink the boat one inch. Useful for calculating how additional gear and stores affect waterline. 711.39 pounds/inch
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