Propeller Slip Calculator 🔄
Calculate propeller slip percentage by comparing theoretical speed to actual GPS speed. Diagnose hull fouling, prop damage, or incorrect pitch.
How to Use the Propeller Slip Calculator
Enter propeller pitch (in inches), engine RPM at cruise, gear ratio, and your actual speed from GPS. The calculator compares theoretical speed to actual speed to determine slip percentage.
Slip of 5–15% is normal for recreational boats. High slip may indicate a fouled hull, damaged propeller, or incorrect prop pitch for your application.
To reduce slip: keep the hull clean, check for propeller damage, and consider re-pitching or resizing the propeller. Consult a marine propeller specialist for persistent high-slip issues.
FAQ
What is propeller slip and why does it matter?
Propeller slip is the difference between your boat's theoretical speed (based on prop pitch and RPM) and actual speed through the water. Some slip is normal (5-15%), but excessive slip indicates wasted energy from hull fouling, prop damage, or incorrect propeller selection.
What is a normal propeller slip percentage?
For recreational boats, 5-15% slip is considered normal. Racing boats may achieve 3-8% slip. Displacement hulls typically show 10-20% slip. If your slip exceeds 20%, investigate potential causes like hull fouling, damaged propeller, or incorrect pitch.
How do I find my propeller pitch?
The pitch is stamped on the propeller hub, usually as two numbers like '13x19' where 13 is diameter and 19 is pitch (both in inches). Pitch represents the theoretical distance the propeller would advance in one revolution through a solid medium.
How do I reduce propeller slip?
Clean the hull regularly, inspect and repair propeller damage, ensure correct propeller pitch for your application, and verify gear ratio. Consider a different propeller if slip is consistently high — a lower pitch prop may be better for heavy displacement boats.