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Sonar
Designer: Bruce Kirby  ·  Builder: Seidelman  ·  First built: 1980
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Sonar
Photo: Ahunt / CC0
About the Sonar

Designed by Bruce Kirby in 1980, this 23-foot sloop has earned recognition as both a competitive one-design racer and capable club boat. With 860 hulls built by Seidelman, the Sonar represents a successful blend of performance and accessibility that has made it popular among sailing programs and racing fleets worldwide. The boat's fractional sloop rig and fin keel with spade rudder configuration delivers responsive handling and solid upwind performance. At 2,100 pounds displacement with nearly half that weight in ballast, the Sonar offers good stability while remaining light enough for exciting sailing in moderate conditions. The generous sail area of 265 square feet provides plenty of power for competitive racing, yet remains manageable for recreational sailing. Bruce Kirby's design philosophy emphasizes clean lines and straightforward systems, making the Sonar an excellent choice for sailing education and club programs. The boat's reputation for durability and relatively simple maintenance has contributed to its longevity in fleets around the world. While primarily suited for protected waters and coastal sailing, the Sonar excels in competitive one-design racing where boat-handling skills and tactics matter more than equipment advantages.

Core Dimensions
LOA (Length Overall) 23.00 ft / 7.01 m
LWL (Waterline Length) 19.92 ft / 6.07 m
Beam 7.83 ft / 2.39 m
Max Draft 3.92 ft / 1.19 m
Displacement 2,100.00 lb / 953 kg
Ballast 930.00 lb / 422 kg
Ballast Type Lead
Sail Area (Reported) 265.00 ft² / 24.62 m²
Design & Construction
Hull Type Fin w/spade rudder
Rigging Type Fractional Sloop
Construction FG
Designer Bruce Kirby
Builder Seidelman
First Built 1980
Number Built 860
Associations Sonar Class Association
Related Sailboats ["Kirby 23" · "Blazer 23 Kirby" · "Ericson 23 2" · "Pearson 23" · "San Juan 23"]
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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
 25.92
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
 44.29
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
 118.61
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
 10.04
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
 2.45
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. 5.98 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
 5.19
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. 557.31 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. 25.94
Rig Dimensions
I (Foretriangle Height) 25.00 ft / 7.62 m
J (Foretriangle Base) 8.90 ft / 2.71 m
P (Mainsail Luff) 27.50 ft / 8.38 m
E (Mainsail Foot) 11.20 ft / 3.41 m
SA Fore 111.25 ft² / 10.34 m²
SA Main 154.00 ft² / 14.31 m²
SA Total (100%) 265.25 ft² / 24.64 m²
Est. Forestay Length 26.54 ft / 8.09 m
How It Compares

vs. Blazer 23 Kirby, Ericson 23 2, Pearson 23

This boat Similar boats
Dimensions
LOA
Sonar ★
23.0 ft
Blazer 23 Kirby
23.0 ft
Ericson 23 2
22.9 ft
Pearson 23
23.0 ft
LWL
Sonar ★
19.9 ft
Blazer 23 Kirby
18.8 ft
Ericson 23 2
19.5 ft
Pearson 23
20.0 ft
Beam
Sonar ★
7.8 ft
Blazer 23 Kirby
7.9 ft
Ericson 23 2
7.9 ft
Pearson 23
8.0 ft
Displacement
Sonar ★
2 lbs
Blazer 23 Kirby
2 lbs
Ericson 23 2
3 lbs
Pearson 23
3 lbs
Ballast
Sonar ★
930 lbs
Blazer 23 Kirby
900 lbs
Ericson 23 2
1 lbs
Pearson 23
1 lbs
Sail Area
Sonar ★
265 sq ft
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
238 sq ft
Performance
SA / Displacement (higher = more powerful)
Sonar ★
25.9
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
16.6
Ballast / Disp (higher = stiffer)
Sonar ★
44.3 %
Blazer 23 Kirby
40.9 %
Ericson 23 2
38.7 %
Pearson 23
37.1 %
Comfort Ratio (higher = more comfortable offshore)
Sonar ★
10.0
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
16.3
Capsize Screening (lower = safer)
Sonar ★
2.45
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
2.11
Displacement / Length (lower = lighter)
Sonar ★
118
Blazer 23 Kirby
148
Ericson 23 2
186
Pearson 23
195
Hull Speed
Sonar ★
6.0 kts
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
6.0 kts
Speed Number (higher = faster)
Sonar ★
5.2
Blazer 23 Kirby
—
Ericson 23 2
—
Pearson 23
2.6
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