20" × 19" Schroef Specificaties

Overview

A 20-inch diameter by 19-inch pitch propeller produces a pitch-to-diameter ratio of 0.95, which falls into the balanced cruising 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.

Schroefspecificaties

Theoretische snelheid per toerental

Typical applications

The 20"×19" size is most commonly fitted to heavy displacement cruisers, sportfishers, and inboards above 250 hp, where the balanced cruising 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 20" and dropping pitch by two inches yields a lower top speed but quicker hole-shot and better load-carrying behaviour, which is why 20"×17" propellers are popular for heavy or family-loaded boats. Raising pitch by two inches to 20"×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 19"×19" prop spins up easier on small engines, while 21"×19" needs a stiffer driveline but bites harder under load.

• 20"×21"
• 19"×19"

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.