Jet Boat Speed Calculator
The jet boat speed calculator estimates the maximum top speed of your jet-driven vessel. By utilizing a modified version of Crouch's formula, it calculates the relationship between engine horsepower, total gross weight, and the hydrodynamic efficiency of your specific hull design.
Performance Estimate
Understanding Jet Boat Performance
Calculating the speed of a jet boat requires a slightly different approach than calculating standard prop-driven vessels. Jet drives inherently experience a 15% to 25% power loss compared to traditional outboard or sterndrive setups due to internal duct friction, impeller slippage, and water pumping mechanics.
The Math: Crouch's Formula
This calculator uses Crouch's Formula: Speed = C × √(Horsepower / Weight). Because of jet pump intake and impeller dynamics, the hydrodynamic "Constant" (C) must be calibrated lower compared to an open-prop boat of identical power.
- Weight sensitivity: Jet boats are highly sensitive to displacement changes. Adding passengers or ballast increases draft, requiring the pump to displace significantly more water to remain on plane.
- Impeller & Wear Ring condition: Peak top speed requires a tight clearance between the impeller blades and the wear ring. Cavitation or worn components reduce thrust and lower real-world speed.
Crouch Constants for Jet Vessels
- Heavy River Jets (C = 165): Heavy gauge aluminum hulls with intake grates designed for river hazards.
- Recreational Jet Boats (C = 185): Production fiberglass jet boats (Yamaha 19-25ft, Sea-Doo, Scarab).
- High-Performance Jets (C = 210): Tunnel hulls, racing jets, or blueprinted pumps with ideal water intake flow.