The Us 21 is aggressively canvassed for its weight, with a quick, snappy motion best suited to day sailing, 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 18.0′, the Us 21 tops out around 5.7 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √18.0′ LWL = 5.7 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
201s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
SA / Displacement
24.8
Performance-oriented — carries a lot of canvas for its weight.
Comfort Ratio
8.7
Quick, snappy motion — better for day sails and racing than long passages.
Capsize Screening
2.68
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
515lbs
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
8.7
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
2.68
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 Us 21 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Us 21
201s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
Amf 2100
240s/nm
Santana 21
264s/nm
Aquarius 21
267s/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° |
2.7 |
3.4 |
3.8 |
3.9 |
| Close Reach60° |
3.2 |
4.1 |
4.6 |
4.8 |
| Beam Reach90° |
4.0 |
5.0 |
5.6 |
5.7 |
| Broad Reach120–135° |
3.7 |
4.6 |
5.2 |
5.4 |
| Run150–180° |
2.9 |
3.7 |
4.2 |
4.3 |
These are simplified estimates based on hull speed (5.7 kts),
SA/D (24.8), 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 Us 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 Us 21.
|
Us 21 |
Amf 2100 |
Aquarius 21 |
Hunter Horizon 21 |
Newport 212 |
Santana 21 |
| Dimensions |
| LOA |
21.3 |
21.1 |
21.0 |
21.2 |
21.2 |
21.3 |
| LWL |
18.0 |
17.6 |
18.3 |
18.8 |
19.1 |
19.3 |
| Beam |
8.0 |
8.0 |
7.8 |
8.0 |
7.7 |
7.5 |
| Displacement |
1 |
2 |
1 |
2 |
1 |
1 |
| Ballast |
200 |
850 |
665 |
1 |
400 |
550 |
| Sail Area |
220 |
209 |
163 |
210 |
— |
189 |
| Performance |
| PHRF |
201 |
240 |
267 |
— |
— |
264 |
| SA/Disp |
24.8 |
19.8 |
17.0 |
16.9 |
— |
21.3 |
| Bal/Disp |
— |
38.6 |
35.0 |
37.5 |
26.7 |
32.4 |
| Comfort |
8.7 |
11.4 |
9.9 |
13.8 |
— |
9.0 |
| Capsize |
2.68 |
2.46 |
2.53 |
2.27 |
— |
2.52 |
| Hull Speed |
5.7 |
5.6 |
5.7 |
5.8 |
— |
5.9 |