Prop Torque Coefficient

MARITIME – PROPULION & PERFORMANCE CALCULATOR Prop Torque Coefficient A precise tool.
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What is the Prop Torque Coefficient & How does it work?

The propeller torque coefficient K_Q is a non‑dimensional parameter that relates the torque required to turn a propeller to the operating and geometric characteristics of the propeller and the surrounding fluid.

It enables designers to compare propeller performance across different sizes and speeds, because it removes the influence of scale and water density.

K_Q = \frac{Q}{\rho \; n^{2} \; D^{5}}
Q = torque (NΒ·m), \rho = water density (kgΒ·m⁻³), n = rev‑s⁻¹, D = propeller diameter (m)

By measuring the torque at a known rotational speed and propeller size, and inserting the water density, the coefficient can be calculated and then used to predict torque for other operating points or to select an appropriate propeller for a vessel.

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Frequently Asked Questions
What is the formula for propeller torque coefficient?
The formula is K_Q = Q / (ρ * n² * D⁡), where Q is torque, ρ is water density, n is revolutions per second, and D is propeller diameter.
Why is the propeller torque coefficient important?
It allows designers to compare propeller performance across different sizes and speeds by removing the influence of scale and water density.
How do I measure the torque required for a propeller?
Torque (Q) can be measured using a dynamometer or torque sensor while the propeller is in operation.
What units are used for water density in this calculation?
Water density (ρ) is typically expressed in kilograms per cubic meter (kg·m⁻³).
Can I use this calculator for any type of fluid, not just water?
This specific formula assumes water as the fluid. For other fluids, adjustments to the formula would be necessary.
How does propeller diameter affect the torque coefficient?
Propeller diameter (D) is raised to the fifth power in the denominator, meaning a larger diameter significantly reduces the torque coefficient for a given torque.
What is the typical range of values for K_Q in maritime applications?
The value of K_Q can vary depending on the specific propeller design and operating conditions, but it typically ranges from around 0.01 to 0.02 for marine propellers.

Results are for informational purposes only and do not constitute professional advice.