Tool · calculator
Propeller slip – calculate slip and theoretical speed
How far the propeller should travel compared with how fast the boat actually moves.
Go to the calculator ↓Results
Theoretical speed
Slipway
Theoretical speed at 0% slip
| Pitch | 3,000 rpm | 4,000 rpm | 5,000 rpm |
|---|---|---|---|
| 13 in | 16 | 21.4 | 26.7 |
| 15 in | 18.5 | 24.7 | 30.9 |
| 17 in | 21 | 28 | 35 |
| 19 in | 23.5 | 31.3 | 39.1 |
| 21 in | 25.9 | 34.6 | 43.2 |
| 23 in | 28.4 | 37.9 | 47.3 |
How we calculate
Theoretical speed (knots) = engine rpm ÷ gear ratio × pitch (inches) × 60 ÷ 72 913. 72 913 is the number of inches in a nautical mile (1 852 m ÷ 0.0254 m). Slip (%) = (1 − measured speed ÷ theoretical speed) × 100. Slip is not a measure of efficiency; a normal value depends on the boat and drive.
Sources: Omni Calculator: Prop Slip Calculator (www.omnicalculator.com) · BIPM: The SI Brochure (nautical mile and knot)