Empirical calm-water resistance estimation for semi-displacement vessels operating between displacement and planing regimes.
Froude Number Fn: —
Reynolds Number: —
Friction Coefficient Cf: —
Residuary Coefficient CR: —
Total Resistance RT: — kN
Delivered Power PD: — kW
The Telfer method is an empirical resistance prediction approach developed for semi-displacement vessels operating in the transitional speed range between conventional displacement and fully planing regimes. It is particularly suited for craft whose operating Froude numbers exceed typical displacement limits but remain below pure planing conditions.
The method was proposed by E. V. Telfer as a practical resistance estimation tool based on systematic model test data for semi-displacement hull forms. It was developed to address a gap between classical displacement-based methods, such as Holtrop–Mennen, and planing theories like Savitsky’s formulation.
Because many fast workboats, patrol craft, and service vessels operate in this intermediate regime, the Telfer method has been widely used for early-stage performance assessment where other methods become unreliable.
Semi-displacement vessels experience both hydrostatic support and dynamic lift. At moderate speeds, wave-making resistance remains significant, while viscous and pressure-related effects begin to dominate as speed increases.
The Telfer method captures this mixed behavior by retaining classical frictional resistance formulations and introducing an empirically derived residuary resistance coefficient that scales with Froude number and hull fullness.
In simplified form, the total resistance of a semi-displacement hull can be written as:
RT = 0.5 · ρ · V² · S · (Cf + CR)
where ρ is water density, V is vessel speed, S is the effective wetted surface area, Cf is the friction coefficient (typically ITTC-1957), and CR represents the residuary resistance coefficient obtained from Telfer correlations.
The accuracy of the Telfer method depends on the correct selection of key hull and operating parameters:
The Telfer method is intended for semi-displacement vessels within a limited but practically important operating envelope:
The Telfer method provides a valuable bridge between displacement and planing resistance prediction techniques. It allows naval architects to estimate resistance and power for vessels that fall outside the reliable range of conventional displacement methods.
Because the formulation is empirical, it is best suited for comparative studies, trend analysis, and preliminary power estimation rather than final design.
The Telfer method is often used in combination with other preliminary resistance and power estimation tools:
Tip: If a vessel’s operating Froude number lies near the upper or lower limit of the Telfer range, it is good practice to compare results with both Holtrop–Mennen and Savitsky methods to ensure consistent performance trends.