The Swan 391 is moderately powered for comfortable coastal cruising, with acceptable motion comfort for coastal passages, and respectable in club racing.
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 33.1′, the Swan 391 tops out around 7.7 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √33.1′ LWL = 7.7 kts
Performance Ratios
Racing handicap, sail-carrying power, stability and comfort — and what each one actually tells you about a day on the water.
PHRF Rating
90s/nm
Cruiser/racer — competitive in club racing, comfortable cruising.
SA / Displacement
17.4
Moderate sail power — a capable coastal cruiser, not overpowered.
Comfort Ratio
29.0
Acceptable coastal comfort — fine for weekends, notice the chop offshore.
Capsize Screening
1.87
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
29.0
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
1.87
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 Swan 391 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Racer 0–90
Cruiser/Racer 90–150
Cruiser 150–210
Swan 391
90s/nm
Cruiser/racer — competitive in club racing, comfortable cruising.
Pearson 40
117s/nm
Intrepid 40
125s/nm
Endeavour 40
147s/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° |
3.1 |
3.9 |
4.4 |
4.6 |
| Close Reach60° |
3.8 |
4.7 |
5.3 |
5.5 |
| Beam Reach90° |
4.6 |
5.8 |
6.5 |
6.8 |
| Broad Reach120–135° |
4.3 |
5.4 |
6.0 |
6.3 |
| Run150–180° |
3.4 |
4.3 |
4.8 |
5.0 |
These are simplified estimates based on hull speed (7.7 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 Swan 391 — 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 Swan 391.
|
Swan 391 |
Endeavour 40 |
Intrepid 40 |
Pearson 40 |
Tartan 40 Offshore |
Valiant 40 2 |
| Dimensions |
| LOA |
39.9 |
40.0 |
40.0 |
39.9 |
40.0 |
39.9 |
| LWL |
33.1 |
32.0 |
32.8 |
31.3 |
36.0 |
34.0 |
| Beam |
12.4 |
13.0 |
12.6 |
12.5 |
13.3 |
12.3 |
| Displacement |
18 |
25 |
20 |
22 |
26 |
22 |
| Ballast |
6 |
9 |
7 |
12 |
10 |
7 |
| Sail Area |
767 |
788 |
749 |
— |
788 |
772 |
| Performance |
| PHRF |
90 |
147 |
125 |
117 |
— |
— |
| SA/Disp |
17.4 |
14.8 |
16.3 |
— |
14.4 |
15.6 |
| Bal/Disp |
— |
36.0 |
36.9 |
53.5 |
— |
34.2 |
| Comfort |
29.0 |
36.9 |
30.5 |
— |
34.3 |
34.3 |
| Capsize |
1.87 |
1.78 |
1.86 |
— |
1.80 |
1.75 |
| Hull Speed |
7.7 |
7.6 |
7.7 |
— |
8.0 |
7.8 |