Propeller Thrust (Marine) Calculator

Work out propeller thrust (marine) instantly with clear inputs, formula shown and shareable results.

About Propeller Thrust (Marine) Calculator

Thrust is useful power divided by speed: T = P x efficiency / V. That relationship explains why thrust is enormous at low speed and falls as the boat speeds up, and why bollard pull, measured at zero speed, must be estimated from a separate empirical relation rather than this formula.

Formula

Propeller thrust

T = shaft power x propulsive efficiency / boat speed (consistent SI units)

Worked example

With the default values below, Propeller Thrust (Marine) Calculator returns Thrust of 60.26. Change any input above and every figure here is recalculated in your browser.

Inputs used

Shaft power delivered: 450 kW
Boat speed: 9 kt
Propulsive efficiency: 62 %
Propeller diameter: 1.2 m

Results

Thrust: 60.26 kN
Thrust: 6,145 kgf
Approximate bollard pull thrust: 4.70 kN
Propeller disc loading: 397.89 kW/m²

Step by step

1Values used
2Propeller thrust
3Thrust= 60.26 kN
4Thrust= 6,145 kgf
5Approximate bollard pull thrust= 4.70 kN
6Propeller disc loading= 397.89 kW/m²

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

Why does the formula fail at zero speed?

Dividing by zero speed gives infinite thrust. At or near zero, momentum theory applies instead, giving thrust proportional to power to the two-thirds power.

What is a typical propulsive efficiency?

Around 55-70% for a well-matched conventional propeller, lower for heavily loaded small props and higher for large slow-turning ones.