Rigging Dimensions
The four foretriangle measurements sailmakers need to quote a new suit.
I ?
37.00 ft
J ?
12.10 ft
P ?
32.00 ft
E ?
14.00 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 | 224.0 | 20.8 |
| 100% ForetriangleI × J ÷ 2 | 223.9 | 20.8 |
| 150% GenoaTypical light-air headsail | 335.8 | 31.2 |
| Storm Jib~50% of foretriangle, high-cut | 111.9 | 10.4 |
| Symmetric SpinnakerEstimated from I, J | 805.9 | 74.9 |
| Total Working Sail AreaMain + 100% foretriangle | 447.9 | 41.6 |
Foretriangle Diagram
Drawn to scale from published I, J, P, E measurements — Masthead Sloop · Ted Irwin design
Performance Ratios
How the Irwin 31 carries its sail relative to its displacement.
SA/D Ratio
15.9
Moderate — comfortable coastal cruiser, not overcanvassed.
Mast Height (above DWL)
— ft
Air draft not published — measure yours before any bridge transit.
Ballast Ratio
40%
Stiff enough to carry a 150% genoa comfortably into moderate breeze.
Typical Sail Inventory
What Irwin 31 owners usually carry and what's worth buying used vs. new.
Mainsail 224.0 ft²
Dacron cross-cut with 2 reef points is standard. Full-batten is a common upgrade.
Replace new
150% Genoa 335.8 ft²
The workhorse headsail. Most boats have one on a furler by now.
Replace new
110% Working Jib ~246 ft²
Good secondary sail for breezy days — used market is strong.
Buy used
Storm Jib 111.9 ft²
Bright orange recommended. Rarely used, hard to justify new.
Buy used
Asymmetric Spinnaker ~806 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 31 — Dacron, laminate, and cruising performance tiers.