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J105
Designer: Rodney S. Johnstone  ·  Builder: J Boats Tillotson Pearson  ·  First built: 1995
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About the J105

Rod Johnstone's design philosophy of creating fast, responsive sailboats reaches its pinnacle in this popular one-design keelboat that has captured the attention of serious racing sailors worldwide. Built as a strict one-design class, this boat emphasizes crew skill over equipment advantages, making it an ideal platform for competitive sailing at both club and championship levels. The design strikes an impressive balance between performance and accessibility, featuring a moderate displacement hull that accelerates quickly in light air while remaining controllable in heavy conditions. Its fractional rig configuration provides excellent upwind performance and allows for precise sail trim adjustments that can make the difference between winning and losing in close fleet racing. What sets this boat apart is its reputation for fostering incredibly tight, tactical racing where boat handling and strategy matter more than budget. The strict class rules ensure that races are won by the best sailors rather than the newest equipment, creating a thriving community of dedicated racers. While primarily designed for one-design racing, the boat's seaworthy characteristics and comfortable cockpit layout make it suitable for spirited day sailing and weekend coastal cruising, though its racing-oriented interior limits extended cruising capabilities.

Core Dimensions
LOA (Length Overall) 34.50 ft / 10.52 m
LWL (Waterline Length) 29.50 ft / 8.99 m
Beam 11.00 ft / 3.35 m
Max Draft 6.50 ft / 1.98 m
Displacement 7,750.00 lb / 3,515 kg
Ballast 3,400.00 lb / 1,542 kg
Sail Area (Reported) 577.00 ft² / 53.61 m²
Design & Construction
Hull Type Fin w/bulb & spade rudder
Rigging Type Fractional Sloop
Construction FG
Designer Rodney S. Johnstone
Builder J Boats Tillotson Pearson
First Built 1995
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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
23.65
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
15.85
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
2.23
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. 7.28
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
4.54
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. 1.0
Rig Dimensions
I (Foretriangle Height) 40.6
J (Foretriangle Base) 13.5
P (Mainsail Luff) 41.5
E (Mainsail Foot) 14.6
ISP (Spinnaker Luff) 42.1
SA Fore 274.05
SA Main 302.95
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