Propeller Slip • Pitch Speed • Shaft RPM • STW • Current Correction • Advance Ratio • Wake • Open-Water Efficiency • Propulsive Efficiency

Propeller Slip Calculator: Pitch, RPM, Speed & Propeller Efficiency

Calculate propeller theoretical speed, shaft RPM, advance per revolution and geometric slip from pitch and vessel speed. Simple mode answers the core slip question quickly. Advanced adds current-corrected speed through water, propeller diameter, wake fraction, advance ratio, thrust deduction, open-water coefficients or direct efficiency, relative-rotative efficiency, drivetrain losses, thrust/torque estimates and a full propulsive-efficiency chain.

Figures represent
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Need much more depth? Click Advanced above.Advanced adds current correction, propeller diameter, wake fraction, advance ratio, thrust deduction, KT/KQ or direct open-water efficiency, relative-rotative efficiency, shaft/gear efficiency, thrust and torque estimates, and RPM/pitch sensitivity.
Fast6 primary controls
Core answerPropeller slip %
ClearSlip ≠ propeller efficiency

Fast Propeller Slip Screen

Enter the effective pitch actually being used. For controllable-pitch propellers, do not assume pitch-setting percentage is linearly equal to geometric pitch unless the maker’s data says so.

metres per revolution.
rpm.
Engine RPM ÷ shaft RPM. Use 1.00 for direct drive.
knots.
knots. Positive = following current, negative = head current. Used only with SOG basis.

Propeller, Shaft & Speed Basis

m/rev at the operating point.
m.
Engine RPM ÷ shaft RPM.
knots. Positive following, negative head current.

Hull–Propeller Interaction

Use vessel/model-test/CFD or approved performance data where available. The tool does not infer these coefficients from vessel type.

Propeller advance speed Vₐ = Vₛ × (1 − w).
kg/m³.

Open-Water Propeller Basis

Used only in direct η₀ mode.

Drivetrain & Operating Check

Use 1.000 for direct drive.
optional kW. Compared with KQ-derived delivered power when coefficients are used.

Measurement Readiness

Engineering limitation: geometric propeller slip is a useful operational indicator, but it is not the same as propeller or propulsive efficiency. Slip can move with current, wake, sea state, draft/trim, hull fouling, propeller condition, manoeuvring and measurement error. Open-water efficiency and full propulsive efficiency require hydrodynamic coefficients or validated vessel-specific data. Use approved propeller curves, model-test/CFD results and sea-trial/performance data for engineering decisions.
Methodology context: Wärtsilä defines propeller slip as the difference between actual ship travel and the theoretical travel from propeller pitch × revolutions, and notes that apparent slip can be negative under following-current or wind conditions. ITTC’s 2024 Hydromechanics Dictionary defines open-water propeller efficiency η₀ = TVₐ/(2πQn), hull efficiency ηH = (1−t)/(1−w), quasi-propulsive efficiency ηD = η₀ηHηR, and overall propulsive efficiency ηP = η₀ηHηRηSηG. ITTC performance procedures use advance speed, advance coefficient, wake fraction, thrust deduction and open-water propeller data as separate hydrodynamic quantities. The tool follows those distinctions and never treats 100 − slip as propeller efficiency.
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