Rigging Dimensions
The four foretriangle measurements sailmakers need to quote a new suit.
I ?
37.60 ft
J ?
11.97 ft
P ?
33.30 ft
E ?
10.20 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 | 169.8 | 15.8 |
| 100% ForetriangleI × J ÷ 2 | 225.0 | 20.9 |
| 150% GenoaTypical light-air headsail | 337.6 | 31.4 |
| Storm Jib~50% of foretriangle, high-cut | 112.5 | 10.5 |
| Symmetric SpinnakerEstimated from I, J | 810.1 | 75.3 |
| Total Working Sail AreaMain + 100% foretriangle | 394.9 | 36.7 |
Foretriangle Diagram
Drawn to scale from published I, J, P, E measurements — Masthead Sloop · Michel Dufour design
Performance Ratios
How the Dufour 31 carries its sail relative to its displacement.
SA/D Ratio
14.0
Moderate — comfortable coastal cruiser, not overcanvassed.
Mast Height (above DWL)
— ft
Air draft not published — measure yours before any bridge transit.
Ballast Ratio
39%
Stiff enough to carry a 150% genoa comfortably into moderate breeze.
Typical Sail Inventory
What Dufour 31 owners usually carry and what's worth buying used vs. new.
Mainsail 169.8 ft²
Dacron cross-cut with 2 reef points is standard. Full-batten is a common upgrade.
Replace new
150% Genoa 337.6 ft²
The workhorse headsail. Most boats have one on a furler by now.
Replace new
110% Working Jib ~248 ft²
Good secondary sail for breezy days — used market is strong.
Buy used
Storm Jib 112.5 ft²
Bright orange recommended. Rarely used, hard to justify new.
Buy used
Asymmetric Spinnaker ~810 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 Dufour 31 — Dacron, laminate, and cruising performance tiers.