Propeller Pitch Speed Calculator

Propeller Pitch Speed Calculator

Propeller pitch is the theoretical distance a propeller would travel through a solid medium in one full revolution - like a screw through wood. This calculator converts pitch, RPM, and gear ratio into estimated boat speed, accounting for real-world propeller slip.

Formula

Propeller RPM = Engine RPM / Gear Ratio
Theoretical Speed = Pitch x Propeller RPM (converted to mph)
Actual Speed = Theoretical Speed x (1 - Slip%)

Example

19-inch pitch propeller, 5,000 engine RPM, 1.5:1 gear ratio, 15% estimated slip:

Propeller RPM = 3,333 → Theoretical Speed = 60.0 mph → Actual Speed ≈ 51.0 mph

What "Slip" Actually Means

In water, the propeller never achieves its full theoretical travel distance per revolution because water isn't a rigid medium - the propeller partially "spins in place" rather than translating perfectly into forward motion, and this efficiency loss is called slip. Typical slip percentages for planing powerboats commonly range from around 10-20%, depending on hull design, propeller selection, and boat loading.