Prop Diameter and Pitch Calculator

Propeller Diameter Formula:

\[ D = k \times \sqrt{\frac{P}{n \times \rho}} \]

Power (P):

Watts (W)

Rotational Speed (n):

rev/s

Water Density (ρ):

kg/m³

Constant (k):

Propeller Diameter (m):

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1. What is a Prop Diameter and Pitch Calculator?

Definition: This calculator estimates the optimal propeller diameter based on power input, rotational speed, water density, and a design constant.

Purpose: It helps marine engineers and boat designers determine appropriate propeller dimensions for efficient propulsion.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ D = k \times \sqrt{\frac{P}{n \times \rho}} \]

Where:

\( D \) — Propeller diameter (meters)
\( k \) — Design constant (dimensionless)
\( P \) — Power input (Watts)
\( n \) — Rotational speed (revolutions per second)
\( \rho \) — Water density (kg/m³)

Explanation: The formula balances power input with rotational speed and water density to determine the most efficient propeller size.

3. Importance of Propeller Sizing

Details: Proper propeller sizing ensures efficient power transfer, optimal fuel consumption, and prevents cavitation or excessive loading.

4. Using the Calculator

Tips: Enter the power in Watts, rotational speed in rev/s, water density (default 1025 kg/m³ for seawater), and design constant (typically 1.0). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the design constant (k)?
A: This empirical constant accounts for propeller efficiency and design characteristics, typically ranging from 0.8 to 1.2.

Q2: What water density should I use?
A: Use 1025 kg/m³ for seawater, 1000 kg/m³ for freshwater, or adjust for temperature variations.

Q3: How do I find the rotational speed?
A: This is your engine's operating RPM divided by 60 (to convert to rev/s).

Q4: Does this include pitch calculation?
A: This calculates diameter only. Pitch is typically 0.6-1.4 times the diameter depending on application.

Q5: What about multi-blade propellers?
A: For 3-5 blade propellers, reduce diameter by 2-5% per additional blade beyond 2.