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Propeller Open-Water Advance Ratio & Efficiency Calculator

In marine propulsion, propeller performance is characterized in open-water (uncoupled from the hull) using non-dimensional coefficients.

Effective water inflow velocity entering propeller plane.

Shaft rotational speed in revolutions per minute.

Propeller tip-to-tip diameter in meters.

Total forward axial thrust force developed.

Torque absorbed by the propeller shaft.

Calculated Result
80.6%

Open-Water Propeller Efficiency (η₀)

Advance Coefficient (J)

1.250

Thrust Coefficient (K_T)

0.1746

Torque Coefficient (K_Q)

0.0431

Calculation Breakdown

  1. J = Va / (n · D)1.250
  2. K_T = T / (ρ · n² · D⁴)0.1746
  3. K_Q = Q / (ρ · n² · D⁵)0.0431
  4. η₀ = (J / 2π) · (K_T / K_Q)80.6%

What Is the Propeller Open-Water Advance Ratio & Efficiency Calculator?

The advance ratio J represents the non-dimensional advance of the propeller through water per revolution.

Open-water efficiency eta_0 is the ratio of useful thrust power delivered to shaft torque power absorbed.

How Does the Propeller Open-Water Advance Ratio & Efficiency Calculator Work?

Converts RPM to rotational frequency n in revolutions per second.

Computes advance ratio J = Va / (n * D).

Calculates non-dimensional thrust coefficient KT and torque coefficient KQ.

Evaluates open-water propeller efficiency eta_0.

Propeller Open-Water Advance Ratio & Efficiency Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

J = \frac{V_a}{n D}, \quad K_T = \frac{T}{\rho n^2 D^4}, \quad K_Q = \frac{Q}{\rho n^2 D^5}, \quad \eta_0 = \frac{J}{2\pi} \frac{K_T}{K_Q}

Standard ITTC open-water non-dimensional propeller hydrodynamic performance formulations.

How to Use the Propeller Open-Water Advance Ratio & Efficiency Calculator

  1. Enter propeller advance speed in m/s and rotational speed in RPM.
  2. Enter propeller diameter in meters.
  3. Specify measured or calculated thrust force (N) and shaft torque (N*m).

Step-by-Step Example Calculation

Bulk Carrier Fixed-Pitch Screw Propeller

Input Values:

advanceSpeedMS:12
propellerRpm:120
propellerDiameterM:4.8
thrustN:380000
torqueNm:450000
Worked Steps: Cruising propulsion operating point on 4-bladed marine propeller.

Understanding Your Result

Typical peak open-water propeller efficiencies range between 60% and 75%.

At low J (bollard pull), efficiency drops toward zero because advance speed is zero.

Factors That Affect the Result

  • Pitch-to-diameter ratio (P/D): Higher pitch ratios shift peak efficiency to higher advance ratios J.
  • Cavitation: High blade loading can trigger suction-side sheet cavitation, collapsing thrust and efficiency.

When Should You Use This Calculator?

  • Propeller selection and matching against ship diesel engine power curves.
  • Analyzing cavitation tunnel and open-water test basin data.

Assumptions & Limitations

  • Assumes open-water undisturbed inflow without wake fraction or hull boundary layer distortions.
  • Seawater density assumed at standard 1025 kg/m³.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Standard International Towing Tank Conference (ITTC) definitions.

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