Free tool · Resistance & effective power

How much power does your hull need?

A first estimate of calm-water resistance and effective power for a displacement hull, using the Holtrop–Mennen statistical method. Enter the main dimensions and see the result at every whole knot.

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01 / The hull

Main dimensions and speed range

Prefilled with the KRISO Container Ship (KCS), a public research hull used in international benchmark studies. Replace the values with your own vessel.

Vessel type Waterline length, L_WL (m) Moulded breadth, B (m) Draught, T (m) Displacement (tonnes)

Speed from (kn) to (kn)

Vessel type only steers the estimates of coefficients you leave blank below. Displacement is in seawater (1,025 kg/m³). Speeds are whole knots, at most 30 steps.

Advanced hull data (optional)

Leave a field blank to use an estimate. The estimate currently used is shown in grey in the empty field.

Block coefficient, C_B Midship coefficient, C_M Waterplane coefficient, C_WP LCB (% of L, + forward of midship) Wetted surface, bare hull (m²) Design speed for LCB estimate (kn) Bulbous bow Bulb transverse area, A_BT (m²) Bulb centroid height, h_B (m) Immersed transom area, A_T (m²) Stern shape Appendage wetted area (m²) Appendage factor, 1+k₂ Add still-air resistance Frontal area above water (m²)

Blank appendage area uses a twin-screw rule of thumb (shaft brackets, bilge keels and rudders). Enter 0 for a bare hull. If you enter an area but no 1+k₂, 1.5 is used. Air resistance uses a drag coefficient of 0.8 and is added outside the Holtrop total, since the method's correlation allowance already includes part of it.

02 / The estimate

Resistance and effective power

Speed vs. power

Resistance components in kN, effective power in kW. Calm water, deep water, clean hull.
Speedkn	Froude no.F_n	FrictionR_F	Formk₁·R_F	AppendagesR_APP	WaveR_W	BulbR_B	TransomR_TR	CorrelationR_A	AirR_AA	TotalkN	Effective powerP_E, kW

Effective power P_E = total resistance × speed. It is the power needed to tow the hull, before propeller, shafting and engine losses, and without margins for weather, fouling or shallow water. Installed engine power is typically considerably higher.

Hull data used in the calculation

What sits behind the numbers?

Holtrop and Mennen fitted regression formulas to model tests and full-scale trials of a large number of ships. The method estimates calm-water resistance from a few hull parameters. It is widely used in early design, when hull lines are not yet available.

Method and formulas

Total resistance R_T = R_F(1+k₁) + R_APP + R_W + R_B + R_TR + R_A, following Holtrop & Mennen (1982) as revised by Holtrop (1984).
Frictional resistance uses the ITTC-1957 correlation line, C_F = 0.075 / (log₁₀Re − 2)², with the wetted surface of the bare hull.
The form factor 1+k₁, the stern coefficient and the wave-resistance formulas follow the 1984 re-analysis. Below F_n = 0.40 the low-speed formula is used, above 0.55 the high-speed formula, and in between the two are interpolated linearly as the 1984 paper prescribes.
Bulb, transom and appendage resistance, and the correlation allowance C_A, use the 1982 formulas, which the 1984 paper retains.
Blank coefficients are estimated with Technocean rules of thumb by vessel type. C_B is calculated from displacement on the waterline length. The wetted surface uses the Holtrop & Mennen approximation. These estimates are not part of the published method.
Seawater 1,025 kg/m³, kinematic viscosity 1.19 × 10⁻⁶ m²/s, air 1.225 kg/m³. The forward draught equals the mean draught. Calculations use unrounded values; results are rounded for display.

Scope, limitations and sources

The result is a statistical estimate for a conventional displacement hull in calm, deep water. Accuracy depends on how closely the hull resembles the ships behind the regression. Multihulls, planing craft, unusual hull forms and shallow-water operation are outside its scope. Propulsion efficiency, propeller design, engine selection, sea margin, fouling, wind and waves are not included.

How close is the estimate? For the KCS example hull at 24 knots, the calculator gives about 1,935 kN and 23.9 MW. Published model tests of the same hull, scaled to full size with the ITTC-1978 method, give about 1,530–1,660 kN and 18.9–20.5 MW. Full-scale CFD for a smooth hull gives about 1,550 kN. The Holtrop estimate is therefore roughly 15–25% higher for this hull, mainly because of a higher wave-resistance component. Deviations of this order are normal for a statistical method, in either direction, and depend on how closely the hull resembles the ships behind the regression.

Commonly quoted parameter ranges (for example L/B 3.9–9.5 and B/T 2.1–4.0) are guidance from later literature, not hard limits from the original papers. The calculator warns when inputs fall outside them.

Holtrop, J. and Mennen, G.G.J. (1982), An approximate power prediction method, International Shipbuilding Progress 29(335), 166–170.
Holtrop, J. (1984), A statistical re-analysis of resistance and propulsion data, International Shipbuilding Progress 31(363), 272–276.
Example hull: KRISO Container Ship (KCS), full-scale main particulars as published by the Tokyo 2015 CFD Workshop (NMRI): L_PP 230.0 m, L_WL 232.5 m, B 32.2 m, T 10.8 m, displacement volume 52,030 m³, bare-hull wetted surface 9,424 m², rudder 115 m², C_M 0.9849, LCB −1.48% L_PP, service speed 24 kn. Waterplane coefficient, bulb and transom areas are not published there and are estimated.
Comparison data for KCS: model-test resistance from Kim, W.J. et al. (2001), Measurement of flows around modern commercial ship models, Experiments in Fluids 31, 567–578, and the Tokyo 2015 CFD Workshop; full-scale CFD from Dogrul, A. et al. (2020), Scale effect on ship resistance components and form factor, Ocean Engineering. Extrapolation to full scale by Technocean, using form factor 1.10 and the ITTC-1978 roughness allowance.

Method review: 2 October 2026.

Need more than a first estimate?

This free tool gives an indication of resistance and effective power. For decisions on hull, propulsion or machinery, Technocean can model your actual vessel, operating profile and propulsion chain in more detail, and help you interpret the results.

Disclaimer

This calculator supports general understanding and early-stage comparison of hull resistance. It is not a substitute for model tests, CFD or a vessel-specific speed–power prediction.

Facts, figures and calculations are presented to the best of Technocean’s knowledge and understanding at the stated review date. Results depend on the inputs and on the simplifying assumptions of the method. No guarantee is given as to completeness, accuracy, actual vessel performance or suitability for a particular purpose.

Users are entirely responsible for checking their inputs and for interpreting and using the outputs. Results should be independently verified before use in design, contractual, operational, commercial or investment decisions.