Hull Speed
The theoretical displacement-mode speed limit — determined by waterline length, not engine or sail power.
5.5 kts
A displacement hull pushes a bow wave whose speed is limited by the waterline length.
With a waterline of 16.7′, the Gem 550 tops out around 5.5 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √16.7′ 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.
Ballast / Displacement
34.6%
Typical cruising ballast — balanced stability and motion underway.
Displacement / Length
110
Ultralight — responsive and fast, but carries less stores.
Hull Speed
5.5kts
Pounds/Inch Immersion
3lbs
Weight needed to sink the hull one inch — loading sensitivity.
PHRF Fleet Position
Where the Gem 550 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Hunter 18
Catalina 18
How It Compares
Side-by-side with the boats most often cross-shopped against the Gem 550.
| Gem 550 | Capri 18 Catalina | Catalina 18 | Condor 55 | Hunter 18 | Neptune 550 | |
|---|---|---|---|---|---|---|
| Dimensions | ||||||
| LOA | 18.0 | 18.0 | 18.0 | 18.0 | 18.0 | 18.0 |
| LWL | 16.7 | 16.3 | 15.8 | 16.4 | 15.5 | 17.2 |
| Beam | 7.9 | 7.6 | 7.8 | 7.4 | 7.5 | 8.0 |
| Displacement | 1 | 1 | 1 | 1 | 1 | 1 |
| Ballast | 397 | 425 | 500 | 595 | 500 | 330 |
| Sail Area | — | 155 | 152 | 193 | 145 | 183 |
| Performance | ||||||
| PHRF | — | — | 289 | — | 282 | — |
| SA/Disp | — | 19.0 | 19.9 | 22.2 | 18.5 | 26.1 |
| Bal/Disp | 34.6 | 28.3 | 37.0 | 36.0 | 35.7 | 27.7 |
| Comfort | — | 9.3 | 8.2 | 10.6 | 9.0 | 6.6 |
| Capsize | — | 2.65 | 2.81 | 2.49 | 2.68 | 3.04 |
| Hull Speed | — | 5.4 | 5.3 | 5.4 | 5.3 | 5.6 |