The Cape Dory 31 is moderately powered for comfortable coastal cruising, with a steady, comfortable ride offshore, designed for cruising comfort rather than 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 23.3′, the Cape Dory 31 tops out around 6.5 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √23.3′ LWL = 6.5 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
198s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
SA / Displacement
15.9
Moderate sail power — a capable coastal cruiser, not overpowered.
Ballast / Displacement
37.8%
Typical cruising ballast — balanced stability and motion underway.
Displacement / Length
408
Heavy displacement — a slow, steady, seakindly hull.
Comfort Ratio
33.3
Good offshore comfort — steady enough for multi-day passages.
Capsize Screening
1.73
Below the 2.0 offshore threshold — acceptable for ocean passages.
Pounds/Inch Immersion
810lbs
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
33.3
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
1.73
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 Cape Dory 31 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Tartan 31
159s/nm
Niagara 31
162s/nm
Irwin 31 Citation
165s/nm
Hunter 31
183s/nm
Cape Dory 31
198s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
Tashiba 31
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 |
3.1 |
3.5 |
3.7 |
| Close Reach60° |
3.0 |
3.8 |
4.3 |
4.4 |
| Beam Reach90° |
3.7 |
4.7 |
5.2 |
5.4 |
| Broad Reach120–135° |
3.4 |
4.3 |
4.8 |
5.0 |
| Run150–180° |
2.7 |
3.5 |
3.9 |
4.0 |
These are simplified estimates based on hull speed (6.5 kts),
SA/D (15.9), 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 Cape Dory 31 — 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 Cape Dory 31.
|
Cape Dory 31 |
Hunter 31 |
Irwin 31 Citation |
Niagara 31 |
Tartan 31 |
Tashiba 31 |
| Dimensions |
| LOA |
31.3 |
31.3 |
31.3 |
31.3 |
31.3 |
31.2 |
| LWL |
23.3 |
26.3 |
26.5 |
24.3 |
26.0 |
25.4 |
| Beam |
9.8 |
10.9 |
11.0 |
10.3 |
10.9 |
10.7 |
| Displacement |
11 |
9 |
9 |
8 |
9 |
13 |
| Ballast |
4 |
4 |
3 |
3 |
3 |
4 |
| Sail Area |
504 |
458 |
474 |
492 |
506 |
552 |
| Performance |
| PHRF |
198 |
183 |
165 |
162 |
159 |
234 |
| SA/Disp |
15.9 |
16.2 |
17.2 |
19.7 |
18.7 |
15.4 |
| Bal/Disp |
37.8 |
41.2 |
36.6 |
44.4 |
43.2 |
— |
| Comfort |
33.3 |
22.4 |
21.1 |
21.1 |
20.9 |
33.5 |
| Capsize |
1.73 |
2.05 |
2.10 |
2.05 |
2.10 |
1.78 |
| Hull Speed |
6.5 |
6.9 |
6.9 |
6.6 |
6.8 |
6.8 |