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Cape Bay 31
Designer: Bruce King  ·  First built: 1977
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About the Cape Bay 31

Designed by renowned naval architect Bruce King and built from 1977 to 1982, this substantial 31-footer represents classic American cruising design from sailing's golden era. With its traditional long keel configuration and transom-hung rudder, the Cape Bay 31 offers the directional stability and sea-kindly motion that made this hull form a favorite among serious cruising sailors. The boat's impressive 11,400-pound displacement and generous 4,500-pound ballast create a stiff, confidence-inspiring platform well-suited for coastal and offshore passages. Its excellent comfort ratio of 29.85 indicates outstanding motion characteristics in a seaway, while the conservative capsize screening value of 1.86 reflects inherent safety for extended cruising. The masthead sloop rig provides versatile sail handling options and reliable performance across varied conditions. Bruce King's design philosophy emphasized seaworthiness over speed, and the Cape Bay 31 delivers accordingly with solid fiberglass construction and thoughtful proportions. The moderate beam and deep draft contribute to impressive tracking ability and windward performance, though docking flexibility may be limited in shallow venues. This design appeals to sailors prioritizing comfort, stability, and blue-water capability over racing performance, making it an enduring choice for serious coastal and passage-making adventures.

Core Dimensions
LOA (Length Overall) 30.92 ft / 9.42 m
LWL (Waterline Length) 23.92 ft / 7.29 m
Beam 10.42 ft / 3.18 m
Max Draft 4.92 ft / 1.50 m
Displacement 11,400.00 lb / 5,171 kg
Ballast 4,500.00 lb / 2,041 kg
Headroom 6.08 ft / 1.85 m
Design & Construction
Hull Type Long keel w/trans. hung rudder
Rigging Type Masthead Sloop
Construction FG
Designer Bruce King
First Built 1977
Last Built 1982
Related Sailboats Ericson 31 Independence
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Performance Ratios
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
 39.47
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
 371.85
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
 29.85
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
 1.86
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. 6.55 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
 1.13
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. 890.58 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. 14.48
Rig Dimensions
I (Foretriangle Height) 38.30 ft / 11.67 m
J (Foretriangle Base) 12.90 ft / 3.93 m
P (Mainsail Luff) 32.50 ft / 9.91 m
E (Mainsail Foot) 12.90 ft / 3.93 m
SA Fore 247.04 ft² / 22.95 m²
SA Main 209.63 ft² / 19.48 m²
SA Total (100%) 456.67 ft² / 42.43 m²
Est. Forestay Length 40.41 ft / 12.32 m
Engine & Accommodations
Engine Make Universal
Engine Type Diesel
Horsepower 16
Fuel Capacity 35 gals / 132 L
Water Capacity 45 gals / 170 L
How It Compares

vs. Ericson 31 Independence

This boat Similar boats
Dimensions
LOA
Cape Bay 31 ★
30.9 ft
Ericson 31 Independence
30.9 ft
LWL
Cape Bay 31 ★
23.9 ft
Ericson 31 Independence
23.9 ft
Beam
Cape Bay 31 ★
10.4 ft
Ericson 31 Independence
10.4 ft
Displacement
Cape Bay 31 ★
11 lbs
Ericson 31 Independence
11 lbs
Ballast
Cape Bay 31 ★
4 lbs
Ericson 31 Independence
4 lbs
Performance
Ballast / Disp (higher = stiffer)
Cape Bay 31 ★
39.5 %
Ericson 31 Independence
39.5 %
Displacement / Length (lower = lighter)
Cape Bay 31 ★
371
Ericson 31 Independence
371
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