Especificações da Hélice 18" × 19"
Relação de passo 1.06: velocidade teórica a 1.000–4.000 RPM
Overview
A 18-inch diameter by 19-inch pitch propeller produces a pitch-to-diameter ratio of 1.06, which falls into the speed-biased, high-revving bracket. The diameter sets the disc area that converts engine torque into thrust, while the pitch sets the theoretical distance the propeller advances per revolution. At 2,500 RPM through a 1.5:1 gearbox this combination posts a theoretical no-slip speed of 26.1 knots; at the 4,000 RPM upper trace the same prop reaches 41.7 knots, with real-world slip pulling those numbers down by 10–20 percent depending on hull loading and bottom condition.
Especificações da hélice
| Diâmetro | 18" |
|---|---|
| Passo | 19" |
| Relação de passo | 1.06 |
Velocidade teórica por RPM
| RPM | Velocidade (0% de derrapagem) | Velocidade (15% de derrapagem) |
|---|---|---|
| 1,000 | 10.4 | 8.9 |
| 1,500 | 15.6 | 13.3 |
| 2,000 | 20.8 | 17.7 |
| 2,500 | 26.1 | 22.1 |
| 3,000 | 31.3 | 26.6 |
| 3,500 | 36.5 | 31.0 |
| 4,000 | 41.7 | 35.4 |
Typical applications
The 18"×19" size is most commonly fitted to offshore center consoles, cruisers, and 150–250 hp powered planing hulls, where the speed-biased, high-revving pitch profile matches the high-performance / racing performance window. Boats inside this class generally cruise between 26.1 and 41.7 knots on the speed chart above. High-RPM, high-pitch combinations are characteristic of light, planing hulls and performance fishing rigs. If your boat tops out far below the 41.7-knot theoretical figure, the propeller is over-pitched for your loaded weight and slip will climb toward the 15-percent column; if you over-rev past the engine's WOT range, the propeller is under-pitched and you should step up one or two inches of pitch.
Compared with adjacent sizes
Holding diameter at 18" and dropping pitch by two inches yields a lower top speed but quicker hole-shot and better load-carrying behaviour, which is why 18"×17" propellers are popular for heavy or family-loaded boats. Raising pitch by two inches to 18"×21" trades acceleration for roughly 2.7 knots of additional theoretical speed at the same RPM. Holding pitch at 19" and changing diameter shifts thrust area: a 17"×19" prop spins up easier on small engines, while 19"×19" needs a stiffer driveline but bites harder under load.
Sizing notes and assumptions
The speed table assumes a 1.5:1 gear reduction and the standard propulsion identity (pitch × RPM) ÷ (gear ratio × 1,215.2) to convert inches-per-minute into knots. Slip estimates of 0 percent (theoretical) and 15 percent (realistic cruising) bracket most clean-bottom planing hulls; expect higher slip on displacement vessels, fouled bottoms, or when towing. Always confirm propeller choice against the engine manufacturer's recommended WOT RPM window — landing inside the band protects the powerhead from lugging or over-revving and is the single biggest factor in long-term engine life.