Ship Towing Tank Scaling & Froude Resistance Calculator
Calculate Froude number, model test scaling ratios, ITTC 1978 friction coefficients, wave-making resistance, and full-scale effective propulsion power.
Model & Ship Scale Dimensions
Towing Tank Dynamometer & Form Factor
Scaling Ratios & Full-Scale Resistance
| Geometric Scale Ratio (λ = Ls / Lm): | -- |
| Froude Number (Fn): | -- |
| Towing Tank Model Speed (Vm): | -- m/s (-- kts) |
| Wave Resistance Coeff (Cw / Cr): | -- |
| Ship Friction Coeff (CFs): | -- |
| Ship Total Resistance Coeff (CTs): | -- |
| Effective Propulsion Power (PE): | -- kW |
| Drag Split (Frictional / Wave): | -- |
Recommended Tools & Equipment
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Frequently Asked Questions
Why can a towing tank not scale both Froude number and Reynolds number simultaneously?
Froude scaling requires model velocity to scale as the square root of the geometric scale ratio (Vm = Vs / sqrt(lambda)), while Reynolds scaling requires velocity to scale inversely (Vm = Vs * lambda). Because water is the testing medium in both cases, satisfying both similitude laws simultaneously is physically impossible without changing fluid viscosity by several orders of magnitude. Froude law is maintained for wave similarity, while Reynolds viscous scaling is corrected mathematically using the ITTC friction line.
What is the Hughes 3D form factor (1 + k) in ITTC 1978 extrapolation?
William Froude originally assumed wave drag and skin friction were independent, treating the hull as an equivalent two-dimensional flat plank. The Hughes method accounts for three-dimensional hull streamline curvature and flow acceleration, which increase viscous pressure drag and shear stress above the 2D plate by a form factor (1 + k), where k is determined from low-speed model runs where wave-making is negligible.
What is the physical meaning of the Froude number Fn in ship design?
The Froude number Fn = V / sqrt(g * L) represents the ratio of inertial forces to gravitational (free-surface wave-making) forces. When Fn is around 0.45 to 0.50, the transverse wave wavelength generated by the bow equals the entire length of the ship. Above this "hull speed" barrier, a displacement hull squats deeply at the stern and must transition into planing mode to travel faster.