Hull Speed
The theoretical displacement-mode speed limit — determined by waterline length, not engine or sail power.
5.9 kts
A displacement hull pushes a bow wave whose speed is limited by the waterline length.
With a waterline of 19.5′, the Four 21 tops out around 5.9 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √19.5′ LWL = 5.9 kts
Performance Ratios
Racing handicap, sail-carrying power, stability and comfort — and what each one actually tells you about a day on the water.
Ballast / Displacement
31.4%
Typical cruising ballast — balanced stability and motion underway.
Displacement / Length
216
Moderate — a good balance of speed and load-carrying ability.
Hull Speed
5.9kts
Pounds/Inch Immersion
3lbs
Weight needed to sink the hull one inch — loading sensitivity.
How It Compares
Side-by-side with the boats most often cross-shopped against the Four 21.
| Four 21 | Alacrity 670 Alacrity 22 | Etap 22 | Jaguar 22 | Kingfisher 20 1 | Westerly 21 | |
|---|---|---|---|---|---|---|
| Dimensions | ||||||
| LOA | 21.5 | 21.5 | 21.7 | 21.5 | 21.6 | 21.5 |
| LWL | 19.5 | 19.3 | 18.7 | 19.3 | 19.3 | 18.8 |
| Beam | 7.3 | 7.7 | 7.9 | 7.7 | 6.9 | 7.8 |
| Displacement | 3 | 2 | 2 | 2 | 2 | 3 |
| Ballast | 1 | — | 1 | 550 | 1 | 1 |
| Sail Area | — | 205 | — | 205 | 177 | 210 |
| Performance | ||||||
| SA/Disp | — | 19.2 | — | 19.2 | 14.0 | 14.2 |
| Bal/Disp | 31.4 | — | 44.0 | 24.4 | — | 45.8 |
| Comfort | — | 11.5 | — | 11.5 | 17.1 | 18.9 |
| Capsize | — | 2.34 | — | 2.34 | 1.94 | 2.01 |
| Hull Speed | — | 5.9 | — | 5.9 | 5.9 | 5.8 |