The Irwin 104 is moderately powered for comfortable coastal cruising, with acceptable motion comfort for coastal passages.
Hull Speed
The theoretical displacement-mode speed limit — determined by waterline length, not engine or sail power.
A displacement hull pushes a bow wave whose speed is limited by the waterline length.
With a waterline of 21.8′, the Irwin 104 tops out around 6.3 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √21.8′ LWL = 6.3 kts
Performance Ratios
Racing handicap, sail-carrying power, stability and comfort — and what each one actually tells you about a day on the water.
SA / Displacement
17.4
Moderate sail power — a capable coastal cruiser, not overpowered.
Comfort Ratio
21.1
Acceptable coastal comfort — fine for weekends, notice the chop offshore.
Capsize Screening
2.16
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
806lbs
Weight needed to sink the hull one inch — loading sensitivity.
Motion & Offshore Suitability
Two ratios that matter most when you're planning passages — how the boat feels in a seaway, and whether the hull geometry is suitable for open ocean.
Comfort Ratio
21.1
Acceptable coastal comfort — fine for weekends, notice the chop offshore.
Under 20 — Snappy, racing motion
20–30 — Acceptable coastal
30–40 — Good offshore comfort
Over 40 — Very comfortable offshore
Capsize Screening Formula
2.16
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Under 2.0 — Acceptable for offshore
Over 2.0 — Coastal / protected waters
PHRF Fleet Position
Where the Irwin 104 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Tanzer 25
180s/nm
Irwin 25
207s/nm
Ericson 25 1
234s/nm
Estimated Speed by Wind
Rough boat speed estimates at different true wind speeds and points of sail — derived from hull speed, SA/D, and displacement, not measured polars.
| Point of Sail |
6 kts TWS |
10 kts TWS |
15 kts TWS |
20 kts TWS |
| Close-hauled40–50° |
2.5 |
3.2 |
3.6 |
3.7 |
| Close Reach60° |
3.0 |
3.9 |
4.3 |
4.5 |
| Beam Reach90° |
3.7 |
4.7 |
5.3 |
5.5 |
| Broad Reach120–135° |
3.5 |
4.4 |
4.9 |
5.1 |
| Run150–180° |
2.8 |
3.5 |
3.9 |
4.1 |
These are simplified estimates based on hull speed (6.3 kts),
SA/D (17.4), and empirical efficiency curves — not instrument-measured
polars. Real-world speed varies with sea state, bottom condition, sail trim, and current.
Speeds in gold approach hull speed;
bold gold means near or at hull speed.
Wind Range & Comfort Envelope
Estimated wind ranges for comfortable sailing on the Irwin 104 — based on sail area, ballast, and displacement characteristics.
Ghost
Sweet Spot
Reef
Heavy
0–7 kts
7–20 kts
20–28 kts
28+ kts
Ghosting
0–7 kts
Light air, motor-sailing likely. Need patience and a light genoa.
Sweet Spot
7–20 kts
Comfortable under full sail. Best speed-to-comfort ratio.
Time to Reef
20–28 kts
Time to shorten sail. Reef the main, swap to a working jib.
Heavy Weather
28+ kts
Storm conditions. Storm jib or bare poles. Seek shelter if coastal.
How It Compares
Side-by-side with the boats most often cross-shopped against the Irwin 104.
|
Irwin 104 |
Cal 2 25 |
Ericson 25 1 |
First Class 8 Beneteau |
Irwin 25 |
Tanzer 25 |
| Dimensions |
| LOA |
25.3 |
25.3 |
25.4 |
25.4 |
25.4 |
25.3 |
| LWL |
21.8 |
22.0 |
21.8 |
21.7 |
20.5 |
21.8 |
| Beam |
10.3 |
9.0 |
9.3 |
8.2 |
8.0 |
9.6 |
| Displacement |
7 |
4 |
5 |
3 |
5 |
4 |
| Ballast |
2 |
2 |
2 |
1 |
2 |
1 |
| Sail Area |
396 |
314 |
325 |
316 |
315 |
— |
| Performance |
| PHRF |
— |
— |
234 |
— |
207 |
180 |
| SA/Disp |
17.4 |
18.5 |
17.8 |
23.8 |
16.4 |
— |
| Bal/Disp |
— |
44.4 |
40.0 |
37.1 |
40.7 |
39.3 |
| Comfort |
21.1 |
16.2 |
17.4 |
12.8 |
23.8 |
— |
| Capsize |
2.16 |
2.18 |
2.17 |
2.24 |
1.83 |
— |
| Hull Speed |
6.3 |
6.3 |
6.3 |
6.2 |
6.1 |
— |