Aquarius 21 vs Viper 640
How do the Aquarius 21 and Viper 640 compare? Below, their dimensions, displacement, sail area and the standard design ratios side by side, followed by a data-driven summary.
Aquarius 21 
Viper 640 | Aquarius 21 | Viper 640 | |
|---|---|---|
| Length overall | 21.0 ft6.40 m | 21.1 ft6.43 m |
| Waterline length | 18.3 ft5.56 m | 19.1 ft5.82 m |
| Beam | 7.8 ft2.38 m | 8.2 ft2.49 m |
| Draft | 4.5 ft1.37 m | 4.5 ft1.37 m |
| Displacement | 1,900 lb862 kg | 750 lb340 kg |
| Ballast | 665 lb302 kg | 262 lb119 kg |
| Sail area | 163 ft²15.1 m² | 211 ft²19.6 m² |
| SA / Displacement | 17.00 | 40.90 |
| Displacement / Length | 140 | 48 |
| Comfort ratio | 9.9 | 3.6 |
| Capsize screening | 2.53 | 3.60 |
| Hull speed (kn) | 5.7 | 5.9 |
Aquarius 21 vs Viper 640: the short version
- The Aquarius 21 and Viper 640 are close in length (21.0 ft6.40 m vs 21.1 ft6.43 m ).
- The Aquarius 21 is heavier, displacing about 153% more, which usually means a steadier but slower-to-accelerate hull.
- On sail area/displacement the Viper 640 carries the more powerful rig (40.9 vs 17.0), favouring lighter-air performance.
- The Aquarius 21 scores higher on the Brewer comfort ratio, suggesting an easier motion in a seaway.
- By the capsize screening formula the Aquarius 21 rates better for offshore work (2.53 vs 3.60).
Ratios are guidelines computed from published specs; condition, layout and gear matter as much as the numbers.