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Achilles 840
Designer: Chris Butler  ·  Builder: Butler Achilles Ltd (Uk)  ·  First built: 1979
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About the Achilles 840

Designed by Chris Butler and built by Butler Achilles Ltd in the UK starting in 1979, this 27.75-foot sailboat represents solid British craftsmanship from an era when builders focused on seaworthiness over speed. The Achilles 840 features a moderate fin keel with rudder on skeg configuration that provides good directional stability and balanced helm characteristics. With a displacement of 5,500 pounds and ballast ratio of 45.5%, this masthead sloop offers reassuring stability for coastal cruising and short offshore passages. The comfort ratio of 18 indicates a relatively stiff, quick motion that experienced sailors will appreciate, while the capsize screening value of 2.04 suggests reasonable stability for offshore work, though prudent seamanship remains essential. The fiberglass hull with balsa-cored deck construction provides good strength-to-weight ratio and insulation properties. Her sail area to displacement ratio of 18.23 delivers respectable performance in moderate conditions, while the hull speed of 6.6 knots sets realistic expectations for passage planning. Best suited for coastal cruising, club racing, and occasional offshore adventures, the Achilles 840 appeals to sailors seeking a well-built, traditionally-proportioned yacht that prioritizes seaworthiness over outright speed. The modest 9.5 horsepower auxiliary engine provides reliable backup power for harbor maneuvering and calm weather motoring.

Core Dimensions
LOA (Length Overall) 27.75 ft / 8.46 m
LWL (Waterline Length) 24.25 ft / 7.39 m
Beam 9.00 ft / 2.74 m
Max Draft 5.00 ft / 1.52 m
Displacement 5,500.00 lb / 2,495 kg
Ballast 2,505.00 lb / 1,136 kg
Ballast Type Iron
Sail Area (Reported) 354.00 ft² / 32.89 m²
Design & Construction
Hull Type Fin with rudder on skeg
Rigging Type Masthead Sloop
Construction FG/balsa core deck
Designer Chris Butler
Builder Butler Achilles Ltd (UK)
First Built 1979
Associations Achilles Yachts Owners Assoc.
Related Sailboats ["Varne 850" · "Contessa 28" · "Etap 28" · "Lancer 28" · "Tanzer 85"]
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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
 18.23
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
 45.55
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
 172.18
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
 18
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
 2.04
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
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
 3.21
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. 779.83 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. 18.21
Rig Dimensions
I (Foretriangle Height) 35.33 ft / 10.77 m
J (Foretriangle Base) 11.46 ft / 3.49 m
P (Mainsail Luff) 31.00 ft / 9.45 m
E (Mainsail Foot) 9.75 ft / 2.97 m
SA Fore 202.44 ft² / 18.81 m²
SA Main 151.13 ft² / 14.04 m²
SA Total (100%) 353.57 ft² / 32.85 m²
Est. Forestay Length 37.14 ft / 11.32 m
Engine & Accommodations
Engine Make Volvo
Engine Model 2001
Engine Type Diesel
Horsepower 9.5
Fuel Capacity 26 gals / 98 L
Water Capacity 18 gals / 68 L
How It Compares

vs. Contessa 28, Etap 28, Lancer 28

This boat Similar boats
Dimensions
LOA
Achilles 840 ★
27.8 ft
Contessa 28
27.7 ft
Etap 28
27.6 ft
Lancer 28
27.7 ft
LWL
Achilles 840 ★
24.3 ft
Contessa 28
22.0 ft
Etap 28
22.7 ft
Lancer 28
23.9 ft
Beam
Achilles 840 ★
9.0 ft
Contessa 28
9.4 ft
Etap 28
10.0 ft
Lancer 28
8.0 ft
Displacement
Achilles 840 ★
5 lbs
Contessa 28
6 lbs
Etap 28
6 lbs
Lancer 28
4 lbs
Ballast
Achilles 840 ★
2 lbs
Contessa 28
2 lbs
Etap 28
2 lbs
Lancer 28
2 lbs
Sail Area
Achilles 840 ★
354 sq ft
Contessa 28
—
Etap 28
319 sq ft
Lancer 28
309 sq ft
Performance
PHRF Rating (lower = faster)
Achilles 840 ★
—
Contessa 28
171 s/nm
Etap 28
222 s/nm
Lancer 28
258 s/nm
SA / Displacement (higher = more powerful)
Achilles 840 ★
18.2
Contessa 28
—
Etap 28
14.5
Lancer 28
17.2
Ballast / Disp (higher = stiffer)
Achilles 840 ★
45.6 %
Contessa 28
40.2 %
Etap 28
38.7 %
Lancer 28
44.9 %
Comfort Ratio (higher = more comfortable offshore)
Achilles 840 ★
18.0
Contessa 28
—
Etap 28
19.7
Lancer 28
18.9
Capsize Screening (lower = safer)
Achilles 840 ★
2.04
Contessa 28
—
Etap 28
2.13
Lancer 28
1.89
Displacement / Length (lower = lighter)
Achilles 840 ★
172
Contessa 28
292
Etap 28
253
Lancer 28
159
Hull Speed
Achilles 840 ★
6.6 kts
Contessa 28
—
Etap 28
6.4 kts
Lancer 28
6.6 kts
Speed Number (higher = faster)
Achilles 840 ★
3.2
Contessa 28
—
Etap 28
1.9
Lancer 28
3.3
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