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Alpa 21
Designer: Sparkman & Stephens  ·  Builder: Alpa  ·  First built: 1976
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About the Alpa 21

Finding comprehensive information about the Alpa 21 can be challenging, as this sailboat represents one of the lesser-documented designs in the sailing world. With limited specifications readily available, prospective buyers will need to dig deeper to uncover the full story of this boat's capabilities and characteristics. What can be determined is that the Alpa 21 likely falls into the small cruiser or daysailer category, making it potentially suitable for coastal sailing and weekend adventures. The 21-foot length suggests a boat designed for ease of handling and trailering, appealing to sailors who value mobility and simplicity over spacious accommodations. Without extensive production records or widespread recognition in sailing communities, the Alpa 21 appears to be either a limited production model or perhaps a regional design that didn't achieve broad market penetration. This scarcity of information could make finding parts, documentation, or knowledgeable repair facilities more challenging for owners. Potential buyers considering an Alpa 21 should conduct thorough research, including seeking out existing owners or sailing forums where firsthand experiences might be shared. A professional marine survey becomes even more critical when evaluating a boat with limited available documentation and support network.

Core Dimensions
LOA (Length Overall) 21.25 ft / 6.48 m
LWL (Waterline Length) 18.60 ft / 5.67 m
Beam 8.16 ft / 2.49 m
Max Draft 4.00 ft / 1.22 m
Displacement 2,868.00 lb / 1,301 kg
Ballast 800.00 lb / 363 kg
Sail Area (Reported) 245.00 ft² / 22.76 m²
Design & Construction
Hull Type Fin w/transom hung rudder
Rigging Type Masthead Sloop
Construction FG
Designer Sparkman & Stephens
Builder Alpa
First Built 1976
Owner Reviews

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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
19.47
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
13.95
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
2.3
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. 5.78
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
3.0
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. 542.31
Rig Dimensions
I (Foretriangle Height) 30.0
J (Foretriangle Base) 8.55
P (Mainsail Luff) 26.0
E (Mainsail Foot) 9.0
SA Fore 128.25
SA Main 117.0
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