Rigging Dimensions
The four foretriangle measurements sailmakers need to quote a new suit.
I ?
37.00 ft
J ?
12.00 ft
P ?
31.67 ft
E ?
9.75 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 | 154.4 | 14.3 |
| 100% ForetriangleI × J ÷ 2 | 222.0 | 20.6 |
| 150% GenoaTypical light-air headsail | 333.0 | 30.9 |
| Storm Jib~50% of foretriangle, high-cut | 111.0 | 10.3 |
| Symmetric SpinnakerEstimated from I, J | 799.2 | 74.2 |
| Total Working Sail AreaMain + 100% foretriangle | 376.4 | 35.0 |
Foretriangle Diagram
Drawn to scale from published I, J, P, E measurements — Masthead Sloop · Ted Irwin design
Performance Ratios
How the Irwin 28 Mk Iv carries its sail relative to its displacement.
SA/D Ratio
15.4
Moderate — comfortable coastal cruiser, not overcanvassed.
Mast Height (above DWL)
— ft
Air draft not published — measure yours before any bridge transit.
Ballast Ratio
41%
Stiff enough to carry a 150% genoa comfortably into moderate breeze.
Typical Sail Inventory
What Irwin 28 Mk Iv owners usually carry and what's worth buying used vs. new.
Mainsail 154.4 ft²
Dacron cross-cut with 2 reef points is standard. Full-batten is a common upgrade.
Replace new
150% Genoa 333.0 ft²
The workhorse headsail. Most boats have one on a furler by now.
Replace new
110% Working Jib ~244 ft²
Good secondary sail for breezy days — used market is strong.
Buy used
Storm Jib 111.0 ft²
Bright orange recommended. Rarely used, hard to justify new.
Buy used
Asymmetric Spinnaker ~799 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 28 Mk Iv — Dacron, laminate, and cruising performance tiers.