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Mistral 31
Designer: Robert Humphries  ·  Builder: Fairey Allday Ltd. (Uk)  ·  First built: 1978
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About the Mistral 31

Designed by Robert Humphries and built by Fairey Allday Ltd. in the UK starting in 1978, this 31-footer represents classic British yacht design philosophy of the late 1970s. The Mistral 31 combines moderate displacement with a modern fin keel and spade rudder configuration, delivering responsive handling characteristics that made it appealing to both cruising sailors and club racers. With a comfort ratio of 16.22, the Mistral 31 sits in the sweet spot for coastal cruising, offering enough stability and seaworthiness for extended passages while maintaining the performance edge that makes daysailing enjoyable. The fractional sloop rig provides excellent balance and sail handling ease, while the fiberglass construction ensures durability and lower maintenance compared to traditional materials of the era. The hull's proportions suggest a yacht optimized for British and European coastal conditions, where versatility between harbor racing and weekend cruising was highly valued. Her SA/Displacement ratio of 20.9 indicates spirited performance in moderate conditions, while the capsize screening formula of 2.25 reflects reasonable stability for coastal and offshore work. This combination of characteristics made the Mistral 31 a practical choice for sailors seeking a boat capable of club racing success and comfortable family cruising.

Core Dimensions
LOA (Length Overall) 31.10 ft / 9.48 m
LWL (Waterline Length) 23.70 ft / 7.22 m
Beam 10.20 ft / 3.11 m
Max Draft 5.20 ft / 1.58 m
Displacement 6,000.00 lb / 2,722 kg
Sail Area (Reported) 430.00 ft² / 39.95 m²
Design & Construction
Hull Type Fin w/spade rudder
Rigging Type Fractional Sloop
Construction FG
Designer Robert Humphries
Builder Fairey Allday Ltd. (UK)
First Built 1978
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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
 20.9
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
 201.21
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
 16.22
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
 2.25
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. 6.52 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. 863.76 pounds/inch
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