Rigging Dimensions
The four foretriangle measurements sailmakers need to quote a new suit.
I ?
39.00 ft
J ?
12.00 ft
P ?
33.17 ft
E ?
9.42 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 | 156.2 | 14.5 |
| 100% ForetriangleI × J ÷ 2 | 234.0 | 21.7 |
| 150% GenoaTypical light-air headsail | 351.0 | 32.6 |
| Storm Jib~50% of foretriangle, high-cut | 117.0 | 10.9 |
| Symmetric SpinnakerEstimated from I, J | 842.4 | 78.3 |
| Total Working Sail AreaMain + 100% foretriangle | 390.2 | 36.3 |
Foretriangle Diagram
Drawn to scale from published I, J, P, E measurements — Masthead Sloop · Ted Irwin design
Performance Ratios
How the Irwin 12 Ton carries its sail relative to its displacement.
SA/D Ratio
16.6
Moderate — comfortable coastal cruiser, not overcanvassed.
Mast Height (above DWL)
42.3 ft
Clears the 65 ft ICW fixed-bridge standard with room to spare.
Ballast Ratio
27%
Light ballast — tends to be tender; reef earlier.
Typical Sail Inventory
What Irwin 12 Ton owners usually carry and what's worth buying used vs. new.
Mainsail 156.2 ft²
Dacron cross-cut with 2 reef points is standard. Full-batten is a common upgrade.
Replace new
150% Genoa 351.0 ft²
The workhorse headsail. Most boats have one on a furler by now.
Replace new
110% Working Jib ~257 ft²
Good secondary sail for breezy days — used market is strong.
Buy used
Storm Jib 117.0 ft²
Bright orange recommended. Rarely used, hard to justify new.
Buy used
Asymmetric Spinnaker ~842 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 Irwin 12 Ton — Dacron, laminate, and cruising performance tiers.