Hull Speed
The theoretical displacement-mode speed limit — determined by waterline length, not engine or sail power.
5.2 kts
A displacement hull pushes a bow wave whose speed is limited by the waterline length.
With a waterline of 15.3′, the Sigma 18 tops out around 5.2 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √15.3′ LWL = 5.2 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
36.9%
Typical cruising ballast — balanced stability and motion underway.
Displacement / Length
154
Moderate — a good balance of speed and load-carrying ability.
Hull Speed
5.2kts
Pounds/Inch Immersion
2lbs
Weight needed to sink the hull one inch — loading sensitivity.
PHRF Fleet Position
Where the Sigma 18 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Hunter 170
Precision 18
Montgomery 17
Venture 17
How It Compares
Side-by-side with the boats most often cross-shopped against the Sigma 18.
| Sigma 18 | Hunter 170 | Montgomery 17 | Precision 18 | Siren 17 | Venture 17 | |
|---|---|---|---|---|---|---|
| Dimensions | ||||||
| LOA | 17.5 | 17.1 | 17.1 | 17.4 | 17.2 | 17.3 |
| LWL | 15.3 | 12.1 | 15.8 | 15.4 | 15.0 | 15.0 |
| Beam | 6.3 | 7.0 | 7.3 | 7.4 | 6.7 | 6.3 |
| Displacement | 1 | 478 | 1 | 1 | 750 | 900 |
| Ballast | 450 | — | 550 | 350 | 130 | 270 |
| Sail Area | — | 150 | 154 | — | 139 | — |
| Performance | ||||||
| PHRF | — | 258 | 264 | 262 | — | 314 |
| SA/Disp | — | 39.3 | 19.7 | — | 27.0 | — |
| Bal/Disp | 36.9 | — | 39.3 | 31.8 | 17.3 | 30.0 |
| Comfort | — | 4.1 | 9.4 | — | 5.9 | — |
| Capsize | — | 3.58 | 2.62 | — | 2.94 | — |
| Hull Speed | — | 4.7 | 5.3 | — | 5.2 | — |