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Harmony 31
Designer: E. G. Van De Stadt  ·  Builder: Tyler Boat Co. Ltd. (Uk)  ·  First built: 1964
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About the Harmony 31

Designed by renowned Dutch naval architect E. G. Van De Stadt, this classic cruising sailboat represents the golden era of offshore sailing design from the mid-1960s. Built by Tyler Boat Co. Ltd. in the UK between 1964 and 1968, only 50 examples of this distinctive yacht were ever produced, making it a relatively rare find today. The Harmony 31's modified full keel configuration and substantial displacement of 10,582 pounds create exceptional stability and seaworthiness, qualities that made Van De Stadt's designs legendary among serious cruising sailors. With nearly 42% of its weight in ballast, this masthead sloop delivers the kind of steady, predictable handling that inspires confidence in challenging offshore conditions. The boat's moderate sail area and conservative design philosophy prioritize safety and comfort over pure performance, reflected in its impressive comfort ratio of 32.2. The capsize screening formula of 1.68 indicates excellent stability for ocean passages, while the hull's lines generate a respectable hull speed for extended cruising. This fiberglass construction represents Tyler's quality British boatbuilding during the 1960s boom in production sailing yachts. For sailors seeking a proven bluewater cruiser with classic lines and Van De Stadt's reputation for seaworthy designs, the Harmony 31 offers time-tested ocean-going capability in a manageable size.

Core Dimensions
LOA (Length Overall) 31.17 ft / 9.50 m
LWL (Waterline Length) 24.44 ft / 7.45 m
Beam 9.19 ft / 2.80 m
Max Draft 4.69 ft / 1.43 m
Displacement 10,582.00 lb / 4,800 kg
Ballast 4,409.00 lb / 2,000 kg
Ballast Type Lead
Sail Area (Reported) 416.00 ft² / 38.65 m²
Design & Construction
Hull Type Modified Full Keel
Rigging Type Masthead Sloop
Construction FG
Designer E. G. van de Stadt
Builder Tyler Boat Co. Ltd. (UK)
First Built 1964
Last Built 1968
Number Built 50
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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
 13.86
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
 41.67
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
 323.61
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
 32.2
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
 1.68
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. 6.62 kn
S# (Speed Number) The Speed Number (S#) is a quick performance index. Higher values indicate a faster, more powerful design relative to its size.
Under 3.0 — Slow cruiser3.0–5.0 — Average cruiser5.0–7.0 — Performance cruiserOver 7.0 — Racer
 1.34
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. 802.53 pounds/inch
SA/Displacement (Calc) Calculated Sail Area to Displacement ratio using actual measured sail dimensions rather than reported values. More precise than the reported SA/Disp figure. 13.86
Rig Dimensions
I (Foretriangle Height) 38.38 ft / 11.70 m
J (Foretriangle Base) 12.30 ft / 3.75 m
P (Mainsail Luff) 32.32 ft / 9.85 m
E (Mainsail Foot) 11.15 ft / 3.40 m
SA Fore 236.04 ft² / 21.93 m²
SA Main 180.18 ft² / 16.74 m²
SA Total (100%) 416.22 ft² / 38.67 m²
Est. Forestay Length 40.30 ft / 12.28 m
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