Rigging Dimensions
The four foretriangle measurements sailmakers need to quote a new suit.
I ?
40.60 ft
J ?
13.50 ft
P ?
41.50 ft
E ?
14.60 ft
Sail Area Breakdown
Calculated from rigging dimensions. Use these as your starting point when ordering a new suit.
| Sail | Area (ft²) | Area (m²) |
|---|---|---|
| MainsailP × E ÷ 2 | 303.0 | 28.1 |
| 100% ForetriangleI × J ÷ 2 | 274.1 | 25.5 |
| 150% GenoaTypical light-air headsail | 411.1 | 38.2 |
| Storm Jib~50% of foretriangle, high-cut | 137.0 | 12.7 |
| Symmetric SpinnakerEstimated from I, J | 986.6 | 91.7 |
| Total Working Sail AreaMain + 100% foretriangle | 577.0 | 53.6 |
Foretriangle Diagram
Drawn to scale from published I, J, P, E measurements — Fractional Sloop · Rodney S. Johnstone design
Performance Ratios
How the J105 carries its sail relative to its displacement.
SA/D Ratio
23.7
Performance-oriented — carries a lot of sail for its weight.
Mast Height (above DWL)
— ft
Air draft not published — measure yours before any bridge transit.
Ballast Ratio
—
Ballast ratio not published.
Typical Sail Inventory
What J105 owners usually carry and what's worth buying used vs. new.
Mainsail 303.0 ft²
Dacron cross-cut with 2 reef points is standard. Full-batten is a common upgrade.
Replace new
150% Genoa 411.1 ft²
The workhorse headsail. Most boats have one on a furler by now.
Replace new
110% Working Jib ~301 ft²
Good secondary sail for breezy days — used market is strong.
Buy used
Storm Jib 137.0 ft²
Bright orange recommended. Rarely used, hard to justify new.
Buy used
Asymmetric Spinnaker ~987 ft²
Popular downwind upgrade — easier than symmetric for shorthanded sailing.
Optional
Replacement Cost Estimator
Get a rough price range for a new mainsail and genoa for the J105 — Dacron, laminate, and cruising performance tiers.