Specifiche Elica 12" × 17"
Rapporto di passo 1.42: velocità teorica a 1.000–4.000 giri/min
Overview
A 12-inch diameter by 17-inch pitch propeller produces a pitch-to-diameter ratio of 1.42, which falls into the highly-geared / over-pitched 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 23.3 knots; at the 4,000 RPM upper trace the same prop reaches 37.3 knots, with real-world slip pulling those numbers down by 10–20 percent depending on hull loading and bottom condition.
Specifiche elica
| Diametro | 12" |
|---|---|
| Passo | 17" |
| Rapporto di passo | 1.42 |
Velocità teorica per giri
| giri/min | Velocità (scorrimento 0%) | Velocità (scorrimento 15%) |
|---|---|---|
| 1,000 | 9.3 | 7.9 |
| 1,500 | 14.0 | 11.9 |
| 2,000 | 18.7 | 15.9 |
| 2,500 | 23.3 | 19.8 |
| 3,000 | 28.0 | 23.8 |
| 3,500 | 32.6 | 27.7 |
| 4,000 | 37.3 | 31.7 |
Typical applications
The 12"×17" size is most commonly fitted to small runabouts, aluminum fishing boats, and 25–75 hp pontoons, where the highly-geared / over-pitched pitch profile matches the planing performance window. Boats inside this class generally cruise between 23.3 and 37.3 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 37.3-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 12" and dropping pitch by two inches yields a lower top speed but quicker hole-shot and better load-carrying behaviour, which is why 12"×15" propellers are popular for heavy or family-loaded boats. Raising pitch by two inches to 12"×19" trades acceleration for roughly 2.7 knots of additional theoretical speed at the same RPM. Holding pitch at 17" and changing diameter shifts thrust area: a 11"×17" prop spins up easier on small engines, while 13"×17" 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.