Calculate propeller slip percentage from pitch speed and actual speed. Estimate efficiency and compare to typical slip ranges for aircraft, boats, and drones.
Propeller slip is the difference between the theoretical pitch speed and the actual forward speed, expressed as a percentage: Slip = (Pitch Speed − Actual Speed) / Pitch Speed × 100. Some slip is always present — a propeller works by accelerating a mass of fluid backward, which requires the blade to meet the fluid at an angle of attack.
This calculator computes propeller slip from three possible input combinations: direct pitch and actual speeds, RPM with pitch and actual speed, or RPM with pitch and a target slip percentage. It handles both MPH and knots for marine and aviation applications.
Typical slip ranges vary dramatically by application: 10-20% for aircraft in cruise, 15-30% for RC planes, 10-20% for planing boats, 30-50% for displacement hulls, and up to 60% for sailboat auxiliary propellers. The reference table helps you compare your calculated slip to expected values.
Understanding slip is essential for propeller selection, boat speed prediction, fuel efficiency analysis, and diagnosing prop/engine matching problems.
Propeller slip is a quick way to compare the theoretical pitch speed to the speed you actually get. It gives a practical read on whether the prop is working in a sensible range or leaving too much advance on the table.
Slip (%) = (V_pitch − V_actual) / V_pitch × 100. Pitch speed = Pitch × RPM (in consistent length/time units). Efficiency ≈ (1 − slip) × η_blade (typically 0.90-0.95).
Result: Slip = 15.4%, lost speed = 20 mph, efficiency ≈ 80%
Slip = (130 − 110)/130 × 100 = 15.4%. This 20 mph difference is the energy going into accelerating the slipstream rather than advancing the vehicle.
Slip is the gap between the pitch speed implied by the propeller and the vehicle's actual speed. A certain amount is unavoidable because the propeller has to accelerate fluid backward to create thrust.
Low slip usually means the prop is well matched to the operating point, while high slip can point to overload, poor pitch choice, damage, or drag. The useful interpretation depends on whether you are looking at an aircraft, boat, or other prop-driven system.
Slip changes with speed, loading, and medium. A prop may show high slip during static testing but a more efficient value once the vehicle is moving, so the number is most useful when compared with the operating condition you care about.
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No. A propeller needs an angle of attack to produce thrust, which requires the blade to "screw" through the fluid faster than the vehicle moves. Zero slip would mean zero thrust.
Overloaded boat (too heavy, too much drag), wrong prop pitch (too high for the power available), damaged blades, growth/fouling, or operating in rough water. Use this as a practical reminder before finalizing the result.
Lower slip generally means better fuel economy at a given speed. However, very low slip can mean the prop is under-pitched and the engine is working harder than necessary.
For planing boats: 10-15% at cruise speed is optimal. Higher slip at low speed (hole shot) is normal. Displacement boats have naturally higher slip (30-50%).
More blades can slightly reduce slip by distributing the thrust over a larger blade area, but the main benefit is smoother operation. Too many blades increase interference and drag.
Slip is highest at zero speed (bollard pull / static thrust) and decreases as speed increases toward the theoretical pitch speed. At very high speed, slip approaches zero but thrust also vanishes.