Ship Froude Number & Wavemaking Regime Calculator

The Froude number characterizes dynamic similarity between water surface wave patterns created by model test hulls and full-scale ships.

It delineates displacement, semi-planing, and fully planing hydrodynamic regimes.

Converts ship speed from knots to meters per second.

Calculates Froude number Fn based on acceleration of gravity and waterline length.

Calculates theoretical displacement hull speed limit (Fn ~ 0.40).

Fn < 0.35: Pure displacement regime; skin friction dominates total resistance.

0.35 <= Fn <= 0.45: Severe wavemaking "hump" region where wave drag accounts for >60% of total resistance.

Fn > 0.50: Semi-planing or planing regime requiring dynamic hydrodynamic lift.

• Waterline length: Longer ships achieve higher speeds before reaching the severe wavemaking resistance barrier.
• Bulbous bow: Creates an out-of-phase wave system that cancels the primary bow wave at design Froude numbers.

• Preliminary hull sizing and propulsion power requirement estimation.
• Scaling towing tank model test results to full-scale ship performance.

• Applies to deep open water; shallow water creates additional critical speed wave restrictions.
• Assumes monohull displacement geometry.