Calculator Inputs
Example Data Table
| RPM | Gear Ratio | Pitch | Slip | Estimated Speed |
|---|---|---|---|---|
| 4600 | 2.20 | 22 | 13% | 37.75 mph |
| 4800 | 2.00 | 24 | 12% | 48.00 mph |
| 5000 | 1.81 | 26 | 10% | 61.22 mph |
Formula Used
The calculator uses propeller speed math with pitch, RPM, ratio, and slip. The no-slip speed formula is:
Speed = RPM × Pitch × (1 − Slip ÷ 100) ÷ (Gear Ratio × 1056)
To estimate required pitch, the formula is rearranged:
Pitch = Speed × Gear Ratio × 1056 ÷ (RPM × (1 − Slip ÷ 100))
Slip from real GPS speed is:
Slip = (Theoretical Speed − Actual Speed) ÷ Theoretical Speed × 100
The number 1056 converts inches per minute into miles per hour.
How to Use This Calculator
Choose the calculation mode first. Enter engine RPM, gear ratio, current pitch, and slip. Add target speed when you want a new pitch. Add actual GPS speed when checking slip. Use load factor for heavier gear, fuel, passengers, or towing. Enter altitude when performance drops at higher lakes. Press Calculate. Review the result above the form. Export the answer as a CSV or PDF file.
Bravo Three Prop Pitch Guide
What This Tool Does
A Bravo Three setup uses counter rotating propellers. Pitch choice affects speed, load, acceleration, and engine RPM. This calculator helps estimate a useful pitch range before testing on water. It does not replace a water trial. It gives a clear starting point.
Why Pitch Matters
Pitch is the forward travel a propeller should make in one turn. Real boats never move that far. Water drag, hull weight, trim, and prop condition create slip. More pitch can raise speed potential. It can also lower RPM. Less pitch can improve launch. It can also raise RPM.
Using Slip Correctly
Slip is not always bad. Every prop has slip. The key is a reasonable value for your boat. Heavy cruisers often show more slip than light performance hulls. Damaged blades add slip. Poor trim can add slip too. Use GPS speed for better checks.
Load and Altitude Effects
Boat load changes everything. Fuel, water, passengers, coolers, and gear can reduce speed. High altitude can reduce engine output. The calculator adds small slip allowances for these conditions. This keeps the estimate more practical.
Wide Open Throttle Check
The best prop usually lets the engine reach its rated wide open throttle range. If RPM is too low, the engine may be overloaded. If RPM is too high, pitch may be too small. This tool estimates RPM movement using a common pitch rule.
Testing the Result
Use the suggested pitch as a planning value. Then test with a normal load. Record RPM, GPS speed, trim, water conditions, and fuel level. Make one change at a time. Clean hulls and healthy props give better numbers. Safe testing gives better decisions.
FAQs
What is Bravo Three prop pitch?
It is the measured forward travel, in inches, that the propeller is designed to move during one full revolution without slip.
Can this calculator select an exact prop?
It estimates a practical pitch. Final choice should be confirmed with GPS speed, RPM, load, engine health, and water testing.
What slip value should I enter?
Many boats start near 10% to 15%. Heavy boats, worn props, poor trim, or rough water may need higher values.
Why does more pitch lower RPM?
More pitch increases propeller load. The engine must work harder each revolution, so wide open throttle RPM can drop.
Why does less pitch improve launch?
Less pitch reduces propeller load. The engine can reach stronger RPM faster, which can improve acceleration and planing.
Should I use GPS speed?
Yes. GPS speed is usually better for slip checks because boat speedometers can be affected by water flow and calibration.
What is a good WOT range?
Use the range from your engine maker. Enter that minimum and maximum range before choosing a final prop pitch.
Can prop condition change results?
Yes. Bent, worn, or damaged blades can increase slip. That can reduce speed and make the pitch estimate less reliable.