What Is the Ship Froude Number & Hydrodynamic Hull Speed Calculator?
The Froude number is a dimensionless parameter comparing vessel velocity to the speed of surface gravity waves of the same length.
How Does the Ship Froude Number & Hydrodynamic Hull Speed Calculator Work?
Normalizes speed by the square root of gravity times waterline length to identify wave-making resistance thresholds.
Ship Froude Number & Hydrodynamic Hull Speed Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Fn = rac{V}{sqrt{g L_{ ext{wl}}}}, quad V_{ ext{hull}} approx 1.34 sqrt{L_{ ext{wl, ft}}} ext{ knots} quad (Fn approx 0.4)
Hydrodynamic Froude number and classic displacement hull speed barrier.
How to Use the Ship Froude Number & Hydrodynamic Hull Speed Calculator
- Enter vessel waterline length in meters and forward vessel speed in knots.
Step-by-Step Example Calculation
75-Meter Coastal Patrol Vessel
Input Values:
waterlineLengthM:75
shipSpeedKnots:18
Worked Steps: Fn = 0.341 (Displacement Regime); theoretical displacement hull speed barrier is 21.0 knots.
Understanding Your Result
Categorizes vessels into displacement (Fn < 0.4), semi-displacement (0.4–1.0), or fully planing (Fn > 1.0) regimes.
Factors That Affect the Result
- Hull fineness ratio, bulbous bow design, and transom stern immersion modify wave resistance.
When Should You Use This Calculator?
- Ship powering estimation, hull form optimization, and model basin scaling using Froude law of similitude.
Assumptions & Limitations
- Assumes deep-water operating conditions; shallow water increases wave resistance at lower speeds.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard naval architecture hydrodynamic formulation.