Jet Boat Impeller Calculator
The jet boat impeller calculator estimates your vessel's theoretical and actual speed based on the pump's mechanical output. Jet drives behave differently than open props, relying on high-velocity water volume. Enter your engine and pump configurations to analyze jet propulsion efficiency.
Understanding Jet Boat Dynamics & Impellers
Unlike traditional prop-driven boats that rely on the mechanical pitch biting into open water, a jet boat relies on Newton's Third Law (Action & Reaction). Water is drawn into an intake beneath the hull, pressurized via an internal **impeller**, and then squeezed out through a restrictive rear nozzle at high velocity.
Impeller Pitch vs. Conventional Propellers
Jet boat impellers are often rated with progressive pitches (e.g., 14/19 or 15/22). The first number indicates the leading edge pitch (designed to scoop water efficiently without instantly stalling), and the second is the trailing exit edge pitch. When using this calculator, you should input the **average effective pitch** or the trailing edge design spec to evaluate maximum potential discharge speeds.
Why Pump Efficiency Matters
Hydrodynamic drag inside the wear ring housing, water turbulence, air entrainment, and nozzle sizing all impact your actual net speed. A pristine, tight-clearance pump typically yields **75% to 85% total system efficiency**. If your wear ring is damaged or you have debris caught in your intake grate, your efficiency percentage can collapse rapidly, leading to high RPM engine revving without corresponding hull speed (known as cavitation).