The Irwin 43 Cc Mki is moderately powered for comfortable coastal cruising, with a steady, comfortable ride offshore.
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 35.5′, the Irwin 43 Cc Mki tops out around 8.0 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √35.5′ LWL = 8.0 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
17.5
Moderate sail power — a capable coastal cruiser, not overpowered.
Ballast / Displacement
30.8%
Typical cruising ballast — balanced stability and motion underway.
Displacement / Length
259
Moderate-heavy — carries provisions well, deliberate in light air.
Comfort Ratio
32.4
Good offshore comfort — steady enough for multi-day passages.
Capsize Screening
1.84
Below the 2.0 offshore threshold — acceptable for ocean passages.
Pounds/Inch Immersion
1lbs
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
32.4
Good offshore comfort — steady enough for multi-day passages.
Under 20 — Snappy, racing motion
20–30 — Acceptable coastal
30–40 — Good offshore comfort
Over 40 — Very comfortable offshore
Capsize Screening Formula
1.84
Below the 2.0 offshore threshold — acceptable for ocean passages.
Under 2.0 — Acceptable for offshore
Over 2.0 — Coastal / protected waters
PHRF Fleet Position
Where the Irwin 43 Cc Mki sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Racer 0–90
Cruiser/Racer 90–150
Cruiser 150–210
Cape Dory 45
120s/nm
Endeavour 43
132s/nm
Irwin 46
138s/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° |
3.2 |
4.1 |
4.6 |
4.7 |
| Close Reach60° |
3.9 |
4.9 |
5.5 |
5.7 |
| Beam Reach90° |
4.8 |
6.0 |
6.8 |
7.0 |
| Broad Reach120–135° |
4.4 |
5.6 |
6.2 |
6.5 |
| Run150–180° |
3.5 |
4.5 |
5.0 |
5.2 |
These are simplified estimates based on hull speed (8.0 kts),
SA/D (17.5), 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 43 Cc Mki — 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 43 Cc Mki.
|
Irwin 43 Cc Mki |
Cape Dory 45 |
Endeavour 43 |
Irwin 43 Cc Mkii |
Irwin 46 |
Morgan 45 4 |
| Dimensions |
| LOA |
45.5 |
45.3 |
45.3 |
45.5 |
45.5 |
45.3 |
| LWL |
35.5 |
33.5 |
35.0 |
35.5 |
37.6 |
36.8 |
| Beam |
13.6 |
13.0 |
14.0 |
13.6 |
13.5 |
13.4 |
| Displacement |
26 |
24 |
33 |
26 |
33 |
22 |
| Ballast |
8 |
9 |
12 |
8 |
12 |
9 |
| Sail Area |
956 |
935 |
1,030 |
1 |
858 |
902 |
| Performance |
| PHRF |
— |
120 |
132 |
— |
138 |
— |
| SA/Disp |
17.5 |
18.1 |
16.1 |
18.7 |
13.4 |
18.2 |
| Bal/Disp |
30.8 |
39.2 |
36.4 |
30.8 |
36.4 |
— |
| Comfort |
32.4 |
32.9 |
39.9 |
32.4 |
39.9 |
27.8 |
| Capsize |
1.84 |
1.81 |
1.75 |
1.84 |
1.69 |
1.91 |
| Hull Speed |
8.0 |
7.8 |
7.9 |
8.0 |
8.2 |
8.1 |