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Irwin Mini Ton
Designer: Irwin/Rogers  ·  Builder: Irwin Yachts  ·  First built: 1978
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About the Irwin Mini Ton

Compact and purposeful, this sailboat emerged from Irwin's efforts to create an affordable entry into the Mini Ton racing class that flourished in the 1970s and early 1980s. Built during an era when one-design racing was gaining momentum among smaller keelboats, the Mini Ton represented Irwin's interpretation of the International Offshore Rule's smallest racing category. The design reflects typical Mini Ton characteristics of the period: a relatively beamy hull with moderate displacement that prioritizes speed and responsive handling over long-distance comfort. Like other boats in this class, it was conceived primarily for competitive sailing and spirited day sailing rather than extended cruising or offshore passages. Irwin's construction approach brought these racing-oriented boats within reach of club racers and weekend sailors who wanted performance without the expense of custom builds. The Mini Ton works best in coastal waters where its nimble handling and racing pedigree can shine. While accommodations are basic by cruising standards, the boat offers enough creature comforts for occasional overnight trips or weekend adventures. Today, these boats appeal to sailors seeking an affordable path into performance sailing or those drawn to the historic Mini Ton class's competitive heritage.

Core Dimensions
LOA (Length Overall) 20.81 ft / 6.34 m
LWL (Waterline Length) 16.50 ft / 5.03 m
Beam 8.00 ft / 2.44 m
Max Draft 4.50 ft / 1.37 m
Min Draft 0.80 ft / 0.24 m
Displacement 1,900.00 lb / 862 kg
Ballast 770.00 lb / 349 kg
Sail Area (Reported) 206.00 ft² / 19.14 m²
Design & Construction
Hull Type Lifting Keel
Rigging Type Fractional Sloop
Construction FG
Designer Irwin/Rogers
Builder Irwin Yachts
First Built 1978
Related Sailboats Irwin 21 Free Spirit · Ultimate 20 · Us 21 · Santana 21 · Cal 21
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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
21.53
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
10.34
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
2.59
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. 5.44
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
3.37
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. 471.65
Rig Dimensions
I (Foretriangle Height) 24.5
J (Foretriangle Base) 8.0
P (Mainsail Luff) 24.5
E (Mainsail Foot) 8.84
SA Fore 98.0
SA Main 108.29
How It Compares

vs. Cal 21, Irwin 21 Free Spirit, Santana 21, Ultimate 20, Us 21

This boat Similar boats
Dimensions
LOA
Irwin Mini Ton ★
20.8 ft
Cal 21
20.5 ft
Irwin 21 Free Spirit
21.0 ft
Santana 21
21.3 ft
Ultimate 20
20.8 ft
Us 21
21.3 ft
LWL
Irwin Mini Ton ★
16.5 ft
Cal 21
16.7 ft
Irwin 21 Free Spirit
16.5 ft
Santana 21
19.3 ft
Ultimate 20
18.0 ft
Us 21
18.0 ft
Beam
Irwin Mini Ton ★
8.0 ft
Cal 21
6.7 ft
Irwin 21 Free Spirit
8.0 ft
Santana 21
7.5 ft
Ultimate 20
8.0 ft
Us 21
8.0 ft
Displacement
Irwin Mini Ton ★
1 lbs
Cal 21
1 lbs
Irwin 21 Free Spirit
1 lbs
Santana 21
1 lbs
Ultimate 20
1 lbs
Us 21
1 lbs
Ballast
Irwin Mini Ton ★
770 lbs
Cal 21
360 lbs
Irwin 21 Free Spirit
750 lbs
Santana 21
550 lbs
Ultimate 20
450 lbs
Us 21
200 lbs
Sail Area
Irwin Mini Ton ★
206 sq ft
Cal 21
196 sq ft
Irwin 21 Free Spirit
202 sq ft
Santana 21
189 sq ft
Ultimate 20
243 sq ft
Us 21
220 sq ft
Performance
PHRF Rating (lower = faster)
Irwin Mini Ton ★
Cal 21
261 s/nm
Irwin 21 Free Spirit
215 s/nm
Santana 21
264 s/nm
Ultimate 20
144 s/nm
Us 21
201 s/nm
SA / Displacement (higher = more powerful)
Irwin Mini Ton ★
21.5
Cal 21
29.5
Irwin 21 Free Spirit
21.9
Santana 21
21.3
Ultimate 20
36.6
Us 21
24.8
Ballast / Disp (higher = stiffer)
Irwin Mini Ton ★
Cal 21
32.7 %
Irwin 21 Free Spirit
41.7 %
Santana 21
32.4 %
Ultimate 20
Us 21
Comfort Ratio (higher = more comfortable offshore)
Irwin Mini Ton ★
10.3
Cal 21
7.6
Irwin 21 Free Spirit
9.8
Santana 21
9.0
Ultimate 20
5.7
Us 21
8.7
Capsize Screening (lower = safer)
Irwin Mini Ton ★
2.59
Cal 21
2.59
Irwin 21 Free Spirit
2.63
Santana 21
2.52
Ultimate 20
3.10
Us 21
2.68
Displacement / Length (lower = lighter)
Irwin Mini Ton ★
Cal 21
106
Irwin 21 Free Spirit
178
Santana 21
105
Ultimate 20
Us 21
Hull Speed
Irwin Mini Ton ★
5.4 kts
Cal 21
5.5 kts
Irwin 21 Free Spirit
5.4 kts
Santana 21
5.9 kts
Ultimate 20
5.7 kts
Us 21
5.7 kts
Speed Number (higher = faster)
Irwin Mini Ton ★
3.4
Cal 21
6.0
Irwin 21 Free Spirit
3.6
Santana 21
5.0
Ultimate 20
7.3
Us 21
4.8
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