The San Juan 21 is aggressively canvassed for its weight, with a quick, snappy motion best suited to day sailing.
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 17.0′, the San Juan 21 tops out around 5.5 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √17.0′ LWL = 5.5 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
258s/nm
Heavy or slow cruiser — all about the journey, not the elapsed time.
SA / Displacement
26.3
Performance-oriented — carries a lot of canvas for its weight.
Comfort Ratio
8.0
Quick, snappy motion — better for day sails and racing than long passages.
Capsize Screening
2.60
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
425lbs
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
8.0
Quick, snappy motion — better for day sails and racing than long passages.
Under 20 — Snappy, racing motion
20–30 — Acceptable coastal
30–40 — Good offshore comfort
Over 40 — Very comfortable offshore
Capsize Screening Formula
2.60
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 San Juan 21 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Holder 20
186s/nm
Precision 21
243s/nm
San Juan 21 2
252s/nm
San Juan 21
258s/nm
Heavy or slow cruiser — all about the journey, not the elapsed time.
Cal 21
261s/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° |
2.6 |
3.3 |
3.7 |
3.8 |
| Close Reach60° |
3.1 |
4.0 |
4.4 |
4.6 |
| Beam Reach90° |
3.9 |
4.9 |
5.4 |
5.5 |
| Broad Reach120–135° |
3.6 |
4.5 |
5.0 |
5.2 |
| Run150–180° |
2.9 |
3.6 |
4.0 |
4.2 |
These are simplified estimates based on hull speed (5.5 kts),
SA/D (26.3), 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 San Juan 21 — based on sail area, ballast, and displacement characteristics.
Ghost
Sweet Spot
Reef
Heavy
0–5 kts
5–16 kts
16–24 kts
24+ kts
Ghosting
0–5 kts
Light air, motor-sailing likely. Need patience and a light genoa.
Sweet Spot
5–16 kts
Comfortable under full sail. Best speed-to-comfort ratio.
Time to Reef
16–24 kts
Time to shorten sail. Reef the main, swap to a working jib.
Heavy Weather
24+ 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 San Juan 21.
|
San Juan 21 |
Cal 21 |
Companion 21 |
Holder 20 |
Precision 21 |
San Juan 21 2 |
| Dimensions |
| LOA |
20.5 |
20.5 |
20.5 |
20.3 |
20.8 |
20.5 |
| LWL |
17.0 |
16.7 |
16.5 |
18.4 |
17.5 |
17.0 |
| Beam |
7.0 |
6.7 |
7.1 |
7.8 |
8.3 |
7.0 |
| Displacement |
1 |
1 |
3 |
1 |
1 |
1 |
| Ballast |
400 |
360 |
1 |
260 |
600 |
400 |
| Sail Area |
190 |
196 |
218 |
194 |
203 |
— |
| Performance |
| PHRF |
258 |
261 |
— |
186 |
243 |
252 |
| SA/Disp |
26.3 |
29.5 |
16.5 |
28.2 |
21.4 |
— |
| Bal/Disp |
— |
32.7 |
32.3 |
22.4 |
32.0 |
32.0 |
| Comfort |
8.0 |
7.6 |
20.0 |
6.1 |
9.4 |
— |
| Capsize |
2.60 |
2.59 |
1.94 |
2.98 |
2.68 |
— |
| Hull Speed |
5.5 |
5.5 |
5.4 |
5.8 |
5.6 |
— |